Internet Engineering Task Force Y. Oiwa
Internet-Draft H. Watanabe
Intended status: Standards Track H. Takagi
Expires: November 19, 2012 RISEC, AIST
B. Kihara
T. Hayashi
Lepidum
Y. Ioku
Yahoo! Japan
May 18, 2012
Mutual Authentication Protocol for HTTP
draft-oiwa-http-mutualauth-11
Abstract
This document specifies a mutual authentication method for the Hyper-
text Transport Protocol (HTTP). This method provides a true mutual
authentication between an HTTP client and an HTTP server using
password-based authentication. Unlike the Basic and Digest
authentication methods, the Mutual authentication method specified in
this document assures the user that the server truly knows the user's
encrypted password. This prevents common phishing attacks: a
phishing attacker controlling a fake website cannot convince a user
that he authenticated to the genuine website. Furthermore, even when
a user authenticates to an illegitimate server, the server cannot
gain any information about the user's password. The Mutual
authentication method is designed as an extension to the HTTP
protocol, and is intended to replace the existing authentication
methods used in HTTP (the Basic method, Digest method, and
authentication using HTML forms).
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on November 19, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Relations to other technologies . . . . . . . . . . . . . 6
1.1.1. Technologies updated or superceded by this proposal . 6
1.1.1.1. HTTP Basic and Digest authentication . . . . . . . 6
1.1.1.2. HTML Form authentication . . . . . . . . . . . . . 6
1.1.2. Technologies not updated by this proposal . . . . . . 7
1.1.2.1. Federated identity/authorization management . . . 7
1.1.2.2. HTTPS and HTTPS client-certificate
authentication . . . . . . . . . . . . . . . . . . 8
1.1.2.3. Relationship with local identity-management
frameworks . . . . . . . . . . . . . . . . . . . . 8
1.1.2.4. HTTP and HTTP authentication architecture . . . . 8
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 9
1.3. Document Structure and Related Documents . . . . . . . . . 9
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 10
2.1. Messages Overview . . . . . . . . . . . . . . . . . . . . 10
2.2. Typical Flows of the Protocol . . . . . . . . . . . . . . 11
2.3. Alternative Flows . . . . . . . . . . . . . . . . . . . . 14
3. Message Syntax . . . . . . . . . . . . . . . . . . . . . . . . 15
3.1. Values . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.1.1. Tokens . . . . . . . . . . . . . . . . . . . . . . . . 16
3.1.2. Strings . . . . . . . . . . . . . . . . . . . . . . . 17
3.1.3. Numbers . . . . . . . . . . . . . . . . . . . . . . . 17
4. Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.1. 401-INIT and 401-STALE . . . . . . . . . . . . . . . . . . 19
4.2. req-KEX-C1 . . . . . . . . . . . . . . . . . . . . . . . . 21
4.3. 401-KEX-S1 . . . . . . . . . . . . . . . . . . . . . . . . 22
4.4. req-VFY-C . . . . . . . . . . . . . . . . . . . . . . . . 23
4.5. 200-VFY-S . . . . . . . . . . . . . . . . . . . . . . . . 24
5. Authentication Realms . . . . . . . . . . . . . . . . . . . . 25
5.1. Resolving Ambiguities . . . . . . . . . . . . . . . . . . 26
6. Session Management . . . . . . . . . . . . . . . . . . . . . . 27
7. Validation Methods . . . . . . . . . . . . . . . . . . . . . . 29
8. Authentication Extensions . . . . . . . . . . . . . . . . . . 30
9. Decision Procedure for Clients . . . . . . . . . . . . . . . . 31
10. Decision Procedure for Servers . . . . . . . . . . . . . . . . 36
11. Authentication Algorithms . . . . . . . . . . . . . . . . . . 38
11.1. Support Functions and Notations . . . . . . . . . . . . . 39
11.2. Default Functions for Algorithms . . . . . . . . . . . . . 40
12. Application Channel Binding . . . . . . . . . . . . . . . . . 41
13. Application for Proxy Authentication . . . . . . . . . . . . . 41
14. Methods to Extend This Protocol . . . . . . . . . . . . . . . 42
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43
16. Security Considerations . . . . . . . . . . . . . . . . . . . 43
16.1. Security Properties . . . . . . . . . . . . . . . . . . . 43
16.2. Denial-of-service Attacks to Servers . . . . . . . . . . . 44
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16.3. Implementation Considerations . . . . . . . . . . . . . . 44
16.4. Usage Considerations . . . . . . . . . . . . . . . . . . . 45
17. Notice on Intellectual Properties . . . . . . . . . . . . . . 45
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 46
18.1. Normative References . . . . . . . . . . . . . . . . . . . 46
18.2. Informative References . . . . . . . . . . . . . . . . . . 47
Appendix A. (Informative) Draft Remarks from Authors . . . . . . 48
Appendix B. (Informative) Draft Change Log . . . . . . . . . . . 48
B.1. Changes in Revision 11 . . . . . . . . . . . . . . . . . . 48
B.2. Changes in Revision 10 . . . . . . . . . . . . . . . . . . 49
B.3. Changes in Revision 09 . . . . . . . . . . . . . . . . . . 49
B.4. Changes in Revision 08 . . . . . . . . . . . . . . . . . . 50
B.5. Changes in Revision 07 . . . . . . . . . . . . . . . . . . 50
B.6. Changes in Revision 06 . . . . . . . . . . . . . . . . . . 50
B.7. Changes in Revision 05 . . . . . . . . . . . . . . . . . . 51
B.8. Changes in Revision 04 . . . . . . . . . . . . . . . . . . 51
B.9. Changes in Revision 03 . . . . . . . . . . . . . . . . . . 51
B.10. Changes in Revision 02 . . . . . . . . . . . . . . . . . . 51
B.11. Changes in Revision 01 . . . . . . . . . . . . . . . . . . 52
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 52
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1. Introduction
This document specifies a mutual authentication method for Hyper-Text
Transport Protocol (HTTP). The method, called "Mutual Authentication
Protocol" in this document, provides a true mutual authentication
between an HTTP client and an HTTP server, using just a simple
password as a credential.
The currently available methods for authentication in HTTP and Web
systems have several deficiencies. The Basic authentication method
[RFC2617] sends a plaintext password to a server without any
protection; the Digest method uses a hash function that suffers from
simple dictionary-based off-line attacks, and people have begun to
think it is obsolete.
The authentication method proposed in this document solves these
problems, substitutes for these existing methods, and serves as a
long-term solution to Web authentication security. It has the
following main characteristics:
o It provides "true" mutual authentication: in addition to assuring
the server that the user knows the password, it also assures the
user that the server truly knows the user's encrypted password at
the same time. This makes it impossible for fake website owners
to persuade users that they have authenticated with the original
websites.
o It uses only passwords as the user's credential: unlike public-
key-based security algorithms, the method does not rely on secret
keys or other cryptographic data that have to be stored inside the
users' computers. The proposed method can be used as a drop-in
replacement to the current authentication methods like Basic or
Digest, while ensuring a much stronger level of security.
o It is secure: when the server fails to authenticate with a user,
the protocol will not reveal any bit of the user's password.
Users can discriminate between true and fake Web servers using their
own passwords by using the proposed method. Even when a user inputs
his/her password to a fake website owned by illegitimate phishers,
the user will certainly notice that the authentication has failed.
Phishers will not be successful in their authentication attempts,
even if they forward the received data from a user to a legitimate
server or vice versa. Users can input sensitive data to the web
forms after confirming that the mutual authentication has succeeded,
without fear of phishing attacks.
The document, along with [I-D.oiwa-http-auth-extension], also
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proposes several extensions to the current HTTP authentication
framework, to replace current widely-used form-based Web
authentication. The extensions provided include:
o Multi-host single authentication within an Internet domain
(Section 5),
o non-mandatory, optional authentication on HTTP (Section 8),
o log out from both server and client side (Section 8), and
o finer control for redirection depending on authentication status
(Section 8).
1.1. Relations to other technologies
1.1.1. Technologies updated or superceded by this proposal
1.1.1.1. HTTP Basic and Digest authentication
The main purpose of this proposal is obviously updating the two
existing HTTP authentication methods, Basic and Digest [RFC2617].
HTTP Basic authentication, as its name suggests, provides very simple
authentication mechanism using plain-text password directly upon the
HTTP transport. HTTP Digest authentication focuses on mitigating the
fundamental weakness of Basic authentication by using MD5-based
hashing to the authentication, but that has almost failed to deploy
due to improper implementations, interoperability problems, and
missing feature implementations before MD5 has deprecated by its
cryptographic weakness. Digest also has a fundamental problem that
the server-side must posses a password-equivalent to perform
authentication, which increases risks of server-side data leakage.
1.1.1.2. HTML Form authentication
Another aim of this protocol is (at least) partially replacing the
HTML form authentication. Because of inflexibility of the HTTP Basic
authentication, recent Web applications tend to use application-level
implementations for user authentication using HTML Forms and Web
browser rendering engines. However, that method has many potential
security weaknesses as same as the HTTP Basic authentication as it
uses plaintext. Considering server-impersonations and existence of
human-forging rogue servers (i.e. phishing), script-based
implementations of hash-based authentication does not help, because
its behavior is completely controlled by the web-page content itself,
which is possibly provided by such a rogue server. This also closes
any possibilities for extending HTML forms to implement cryptography,
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as its user-interface could not be prevented from being imitated
using plain-text forms. Using HTTP-level authentication is better in
this field, because it is under the control of the client software
(Web browsers), which can enforce security checks regardless of
server-provided contents.
Of course, we could not ignore the strong reasons of favoring Form
authentication over Basic authentication: its flexibility. HTTP
authentication framework lacks many features for recent Web
applications, mainly for interactions between HTTP-level
authentications and application-level management of "authentication
sessions". As long as current HTTP-layer (and lower-layer)
authentication are used, the new method would share the same problem.
To solve this problem, this protocol has a companion mechanism for
application-level control of authentication behaviors as a separate
draft [I-D.oiwa-http-auth-extension]. By using this additional
mechanism, Web applications can implement most of these required
features as easy as just calling an already-provided API for them.
1.1.2. Technologies not updated by this proposal
1.1.2.1. Federated identity/authorization management
There are several technologies (protocols, frameworks, or systems)
for managing authentications/authorizations involving multiple-
parties: some of those examples are OAuth, OpenID Connect, SAML etc.
These technologies can be further divided to two categories:
federated authentication and authorization delegation, although some
of these technologies cover both.
Federated authentication provides so-called "three-legged
authentication": provided the result of user authentication to a
single entity (identity provider) and the user's consent, the
mechanism can provide other entities assertion of the user's identity
without performing a separate identity management by every entity.
Authorization delegation gives a mechanism for transferring a part of
the user's privilege on an entity (resource owners) to another entity
without requiring users give away the full credential for the
authentication.
Essentially, both of those technologies are transforming a result of
conventional, one-by-one (two-legged) authentication into a multi-
party privilege management. The purpose of this protocol is to
secure the very part of the two-legged authentication, and so it can
be naturally combined with existing federated management frameworks
for increasing security of the entire system.
Additionally, this protocol can provide a secure peer-to-peer shared
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key generated during authentication to the higher-layer applications
Section 12. These keys can be possibly used by such federating
mechanisms in future for simplifying/securing the framework.
1.1.2.2. HTTPS and HTTPS client-certificate authentication
This protocol will not replace the wide-spread and widely-accepted
technology of SSL/TLS and HTTPS. This protocol will still relying on
the HTTPS for the integrity and secrecy of the HTTP payload. This
protocol ensures users the integrity and secrecy of the
authentication credentials, and authenticity of the talking peer
server.
Client certificate (and other public-key-based) authentications have
a fair-amount of applications (mainly for high-assurance
applications), and there are possible needs for redesigning/updating
the whole framework. However, currently public-key-based user-
authentication and connection-based user identification is out-of-
scope of this proposal.
1.1.2.3. Relationship with local identity-management frameworks
There are several existing frameworks for managing user identity of
tightly-managed, closed group of users, such as Kerberos etc. Some
of these have defined a bridging protocol for HTTP authentication.
This protocol does not currently aim to replace such existing
frameworks.
More precisely, requirements for those framework and usual Web user
authentication differ fundamentally. In such framework, user
authentication in performed first, and the result of the
authentication tends to be shared in all applications, sometimes even
shared regardless of the underlying protocols. In those systems, it
is almost never likely to use a multiple identity to be used inside a
single server and inside a single client machine at the same time.
In such applications, connection-based or even a machine-based
authentication can be used without a trouble. This is not a case for
the general Web authentication applications.
1.1.2.4. HTTP and HTTP authentication architecture
Although HTTP and generic HTTP authentication architecture lacks some
required features (see above), the whole structure of per-request,
per-resource authentication is well-suited for general Web
applications compared with connection-based or machine-based
authentication/authorization framework (those which tie user identity
to either connections or machines). The whole protocol in this
specification is designed on top of the framework of
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[I-D.ietf-httpbis-p7-auth]. Small extensions to the framework in
this specification and [I-D.oiwa-http-auth-extension], which are
designed for filling the missing features, are carefully designed so
that it can be implemented easily only by the client-side without
changing the whole framework.
1.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
The terms "encouraged" and "advised" are used for suggestions that do
not constitute "SHOULD"-level requirements. People MAY freely choose
not to include the suggested items regarding [RFC2119], but complying
with those suggestions would be a best practice; it will improve the
security, interoperability, and/or operational performance.
This document distinguishes the terms "client" and "user" in the
following way: A "client" is an entity understanding and talking HTTP
and the specified authentication protocol, usually computer software;
a "user" is a (usually natural) person who wants to access data
resources using "a client".
The term "natural numbers" refers to the non-negative integers
(including zero) throughout this document.
This document treats target (codomain) of hash functions to be
natural numbers. The notation OCTETS(H(s)) gives a usual octet-
string output of hash function H applied to string s.
1.3. Document Structure and Related Documents
The entire document is organized as follows:
o Section 2 presents an overview of the protocol design.
o Sections 3 to 10 define a general framework of the Mutual
authentication protocol. This framework is independent of
specific cryptographic primitives.
o Section 11 describes properties needed for cryptographic
algorithms used with this protocol framework, and defines a few
functions which will be shared among such cryptographic
algorithms.
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o The sections after that contain general normative and informative
information about the protocol.
o The appendices contain some information that may help developers
to implement the protocol.
In addition, there are two companion documents which are referred
from/related to this specification:
o [I-D.oiwa-http-mutualauth-algo]: defines a cryptographic
primitives which can be used with this protocol framework. [draft
note: it is separated so that it may be replaced with another
crypto in future. We need at least one example for testing/
implementing this protocol, so here it is.]
o [I-D.oiwa-http-auth-extension]: defines a small but useful
extensions to the current HTTP authentication framework so that it
can support application-level semantics of existing Web systems.
2. Protocol Overview
The protocol, as a whole, is designed as a natural extension to the
HTTP protocol [I-D.ietf-httpbis-p1-messaging] using a framework
defined in [I-D.ietf-httpbis-p7-auth]. Internally, the server and
the client will first perform a cryptographic key exchange, using the
secret password as a "tweak" to the exchange. The key-exchange will
only succeed when the secrets used by the both peers are correctly
related (i.e. generated from the same password). Then, both peers
will verify the authentication results by confirming the sharing of
the exchanged key. This section describes a brief image of the
protocol and the exchanged messages.
2.1. Messages Overview
The authentication protocol uses seven kinds of messages to perform
mutual authentication. These messages have specific names within
this specification.
o Authentication request messages: used by the servers to request
clients to start mutual authentication.
* 401-INIT message: a general message to start the authentication
protocol. It is also used as a message indicating an
authentication failure.
* 200-Optional-INIT message: a variant of the 401-INIT message
indicating that an authentication is not mandatory.
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* 401-STALE message: a message indicating that it has to start a
new authentication trial.
o Authenticated key exchange messages: used by both peers to perform
authentication and the sharing of a cryptographic secret.
* req-KEX-C1 message: a message sent from the client.
* 401-KEX-S1 message: a message sent from the server as a
response to a req-KEX-C1 message.
o Authentication verification messages: used by both peers to verify
the authentication results.
* req-VFY-C message: a message used by the client, requesting
that the server authenticates and authorizes the client.
* 200-VFY-S message: a successful response used by the server,
and also asserting that the server is authentic to the client
simultaneously.
In addition to the above, either a request or a response without any
HTTP headers related to this specification will be hereafter called a
"normal request" or a "normal response", respectively.
2.2. Typical Flows of the Protocol
In typical cases, the client access to a resource protected by the
Mutual authentication will follow the following protocol sequence.
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Client Server
| |
| ---- (1) normal request ---------> |
GET / HTTP/1.1 |
| |
| <---------------- (2) 401-INIT --- |
| 401 Authentication Required
| WWW-Authenticate: Mutual realm="a realm"
| |
[user, | |
pass]-->| |
| ---- (3) req-KEX-C1 -------------> |
GET / HTTP/1.1 |
Authorization: Mutual user="john", |--> [user DB]
kc1="...", ... |<-- [user info]
| |
| <-------------- (4) 401-KEX-S1 --- |
| 401 Authentication Required
| WWW-Authenticate: Mutual sid=..., ks1="...", ...
| |
[compute] (5) compute session secret [compute]
| |
| |
| ---- (6) req-VFY-C --------------> |
GET / HTTP/1.1 |--> [verify (6)]
Authorization: Mutual sid=..., |<-- OK
vkc="...", ... |
| |
| <--------------- (7) 200-VFY-S --- |
[verify | 200 OK |
(7)]<--| Authentication-Info: Mutual vks="..."
| |
v v
Figure 1: Typical communication flow for first access to resource
o As usual in general HTTP protocol designs, a client will at first
request a resource without any authentication attempt (1). If the
requested resource is protected by the Mutual authentication, the
server will respond with a message requesting authentication
(401-INIT) (2).
o The client processes the body of the message, and waits for the
user to input the user name and a password. If the user name and
the password are available, the client will send a message with
the authenticated key exchange (req-KEX-C1) to start the
authentication (3).
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o If the server has received a req-KEX-C1 message, the server looks
up the user's authentication information within its user database.
Then the server creates a new session identifier (sid) that will
be used to identify sets of the messages that follow it, and
responds back with a message containing a server-side
authenticated key exchange value (401-KEX-S1) (4).
o At this point (5), both peers calculate a shared "session secret"
using the exchanged values in the key exchange messages. Only
when both the server and the client have used secret credentials
generated from the same password will the session secret values
match. This session secret will be used for the actual access
authentication after this point.
o The client will send a request with a client-side authentication
verification value (req-VFY-C) (6), generated from the client-
owned session secret. The server will check the validity of the
verification value using its own session secret.
o If the authentication verification value from the client was
correct, it means that the client definitely owns the credential
based on the expected password (i.e. the client authentication
succeeded.) The server will respond with a successful message
(200-VFY-S) (7). Contrary to the usual one-way authentication
(e.g. HTTP Basic authentication or POP APOP authentication), this
message also contains a server-side authentication verification
value.
When the client's verification value is incorrect (e.g. because
the user-supplied password was incorrect), the server will respond
with the 401-INIT message (the same one as used in (2)) instead.
o The client MUST first check the validity of the server-side
authentication verification value contained in the message (7).
If the value was equal to the expected one, the server
authentication succeeded.
If it is not the value expected, or if the message does not
contain the authentication verification value, it means that the
mutual authentication has been broken for some unexpected reason.
The client MUST NOT process any body or header values contained in
this case. (Note: This case should not happen between a
correctly-implemented server and a client.)
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2.3. Alternative Flows
As shown above, the typical flow for a first authenticated request
requires three request-response pairs. To reduce the protocol
overhead, the protocol enables several short-cut flows which require
fewer messages.
o (case A) If the client knows that the resource is likely to
require the authentication, the client MAY omit the first
unauthenticated request (1) and immediately send a key exchange
(req-KEX-C1 message). This will reduce one round-trip of
messages.
o (case B) If both the client and the server previously shared a
session secret associated with a valid session identifier (sid),
the client MAY directly send a req-VFY-C message using the
existing session identifier and corresponding session secret.
This will further reduce one round-trip of messages.
In such cases, the server MAY have thrown out the corresponding
sessions from the session table. In this case, the server will
respond with a 401-STALE message, indicating a new key exchange is
required. The client SHOULD retry constructing a req-KEX-C1
message in this case.
Figure 2 depicts the shortcut flows described above. Under the
appropriate settings and implementations, most of the requests to
resources are expected to meet both the criteria, and thus only one
round-trip of request/responses will be required in most cases.
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(A) omit first request
(2 round trips)
Client Server
| |
| --- req-KEX-C1 ----> |
| |
| <---- 401-KEX-S1 --- |
| |
| ---- req-VFY-C ----> |
| |
| <----- 200-VFY-S --- |
| |
(B) reusing session secret
(B-1) key available (B-2) key expired
(1 round trip) (3 round trips)
Client Server Client Server
| | | |
| ---- req-VFY-C ----> | | --- req-VFY-C -------> |
| | | |
| <----- 200-VFY-S --- | | <------- 401-STALE --- |
| | | |
| --- req-KEX-C1 ------> |
| |
| <------ 401-KEX-S1 --- |
| |
| --- req-VFY-C -------> |
| |
| <------- 200-VFY-S --- |
| |
Figure 2: Several alternative flows on protocol
For more details, see Sections 9 and 10.
3. Message Syntax
Throughout this specification, The syntax is denoted in the extended
augmented BNF syntax defined in [I-D.ietf-httpbis-p1-messaging] and
[RFC5234]. The following elements are quoted from [RFC5234],
[I-D.ietf-httpbis-p1-messaging] and [I-D.ietf-httpbis-p7-auth]:
DIGIT, ALPHA, SP, auth-scheme, quoted-string, auth-param, header-
field, token, challenge, and credential.
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The Mutual authentication protocol uses three headers:
WWW-Authenticate (in responses with status code 401), Authorization
(in requests), and Authentication-Info (in responses other than 401
status). These headers follow a common framework described in
[I-D.ietf-httpbis-p7-auth]. The detailed meanings for these headers
are contained in Section 4.
The framework in [I-D.ietf-httpbis-p7-auth] defines the syntax for
the headers WWW-Authenticate and Authorization as the syntax elements
"challenge" and "credentials", respectively. The "auth-scheme"
contained in those headers MUST be "Mutual" throughout this protocol
specification. The syntax for "challenge" and "credentials" to be
used with the "Mutual" auth-scheme SHALL be name-value pairs (#auth-
param), not the "b64token" defined in [I-D.ietf-httpbis-p7-auth].
The Authentication-Info: header used in this protocol SHALL contain
the value in same syntax as those the "WWW-Authenticate" header, i.e.
the "challenge" syntax element.
In HTTP, the WWW-Authenticate header may contain more than one
challenges. Client implementations SHOULD be aware of and be capable
of handle those cases correctly.
3.1. Values
The parameter values contained in challenge/credentials MUST be
parsed strictly conforming to the HTTP semantics (especially un-
quoting of the string parameter values). In this protocol, those
values are further categorized into the following value types: tokens
(bare-token and extensive-token), string, integer, hex-fixed-number,
and base64-fixed-number.
For clarity, implementations are encouraged to use the canonical
representations specified in the following subsections for sending
values. Recipients SHOULD accept both quoted and unquoted
representations interchangeably as specified in HTTP.
3.1.1. Tokens
For sustaining both security and extensibility at the same time, this
protocol defines a stricter sub-syntax for the "token" to be used.
The extensive-token values SHOULD follow the following syntax (after
HTTP value parsing):
bare-token = 1*(DIGIT / ALPHA / "-" / "_")
extension-token = "-" bare-token 1*("." bare-token)
extensive-token = bare-token / extension-token
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Figure 3: BNF syntax for token values
The tokens (bare-token and extension-token) are case insensitive;
Senders SHOULD send these in lower-case, and receivers MUST accept
both upper- and lower-cases. When tokens are used as (partial)
inputs to any hash or other mathematical functions, it MUST always be
used in lower-case.
Extensive-tokens are used in this protocol where the set of
acceptable tokens may include non-standard extensions. Any non-
standard extensions of this protocol SHOULD use the extension-tokens
with format "-<bare-token>.<domain-name>", where <domain-name> is a
validly registered (sub-)domain name on the Internet owned by the
party who defines the extensions.
Bare-tokens and extensive-tokens are also used for parameter names
(of course in the unquoted form). Requirements for using the
extension-token for the parameter names are the same as the above.
The canonical format for bare-tokens and tokens are unquoted tokens.
3.1.2. Strings
All character strings outside ASCII character sets MUST be encoded
using the UTF-8 encoding [RFC3629] for the ISO 10646-1 character set
[ISO.10646-1.1993], without any leading BOM characters. Both peers
are RECOMMENDED to reject any invalid UTF-8 sequences that might
cause decoding ambiguities (e.g., containing <"> in the second or
later byte of the UTF-8 encoded characters).
If strings are representing a domain name or URI that contains non-
ASCII characters, the host parts SHOULD be encoded as it is used in
the HTTP protocol layer (e.g. in a Host: header); under current
standards it will be the one defined in [RFC5890]. It SHOULD use
lower-case ASCII characters.
The canonical format for strings are quoted-string.
3.1.3. Numbers
The following syntax definitions gives a syntax for number-type
values:
integer = "0" / (%x31-39 *DIGIT) ; no leading zeros
hex-fixed-number = 1*(2(DIGIT / %x41-46 / %x61-66))
base64-fixed-number = 1*( ALPHA / DIGIT /
"-" / "." / "_" / "~" / "+" / "/" ) *"="
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Figure 4: BNF syntax for number types
The syntax definition of the integers only allows representations
that do not contain extra leading zeros.
The numbers represented as a hex-fixed-number MUST include an even
number of characters (i.e. multiples of eight bits). Those values
are case-insensitive, and SHOULD be sent in lower-case. When these
values are generated from any cryptographic values, they SHOULD have
their "natural length": if these are generated from a hash function,
these lengths SHOULD correspond to the hash size; if these are
representing elements of a mathematical set (or group), its lengths
SHOULD be the shortest for representing all the elements in the set.
For example, any results of SHA-256 hash function will be represented
by 64 characters, and any elements in 2048-bit prime field (modulo a
2048-bit integer) will be represented by 512 characters, regardless
of how much 0's will be appear in front of such representations.
Session-identifiers and other non-cryptographically generated values
are represented in any (even) length determined by the side who
generates it first, and the same length SHALL be used throughout the
all communications by both peers.
The numbers represented as base64-fixed-number SHALL be generated as
follows: first, the number is converted to a big-endian radix-256
binary representation as an octet string. The length of the
representation is determined in the same way as mentioned above.
Then, the string is encoded using the Base 64 encoding [RFC4648]
without any spaces and newlines. Implementations decoding base64-
fixed-number SHOULD reject any input data with invalid characters,
excess/insufficient paddings, or non-canonical pad bits (See Sections
3.1 to 3.5 of [RFC4648]).
The canonical format for integer and hex-fixed-number are unquoted
tokens, and that for base64-fixed-number is quoted-string.
4. Messages
In this section we define the seven kinds of messages used in the
authentication protocol along with the formats and requirements of
the headers for each message.
To determine which message are expected to be sent, see Sections 9
and 10.
In the descriptions below, the type of allowable values for each
header parameter is shown in parenthesis after each parameter name.
The "algorithm-determined" type means that the acceptable value for
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the parameter is one of the types defined in Section 3, and is
determined by the value of the "algorithm" parameter. The parameters
marked "mandatory" SHALL be contained in the message. The parameters
marked "non-mandatory" MAY either be contained or omitted in the
message. Each parameter SHALL appear in each headers exactly once at
most.
All credentials and challenges MAY contain any parameters not
explicitly specified in the following sections. Recipients who do
not understand such parameters MUST silently ignore those. However,
all credentials and challenges MUST meet the following criteria:
o For responses, the parameters "reason", any "ks*" (where * stands
for any decimal integers), and "vks" are mutually exclusive: any
challenge MUST NOT contain two or more parameters among them.
They MUST NOT contain any "kc*" and "vkc" parameters.
o For requests, the parameters "kc*" (where * stands for any decimal
integers), and "vks" are mutually exclusive and any challenge
MUST NOT contain two or more parameters among them. They MUST NOT
contain any "ks*" and "vks" parameters.
4.1. 401-INIT and 401-STALE
Every 401-INIT or 401-STALE message SHALL be a valid HTTP 401-status
(Authentication Required) message containing one (and only one:
hereafter not explicitly noticed) "WWW-Authenticate" header
containing a "reason" parameter in the challenge. The challenge
SHALL contain all of the parameters marked "mandatory" below, and MAY
contain those marked "non-mandatory".
version: (mandatory extensive-token) should be the token
"-draft11" in this specification. The behavior is
undefined when other values are specified.
algorithm: (mandatory extensive-token) specifies the
authentication algorithm to be used. The value MUST
be one of the tokens specified in
[I-D.oiwa-http-mutualauth-algo] or other supplemental
specification documentation.
validation: (mandatory extensive-token) specifies the method of
host validation. The value MUST be one of the tokens
described in Section 7, or the tokens specified in
other supplemental specification documentation.
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auth-domain: (non-mandatory string) specifies the authentication
domain, the set of hosts for which the authentication
credentials are valid. It MUST be one of the strings
described in Section 5. If the value is omitted, it
is assumed to be the "single-port" type domain in
Section 5.
realm: (mandatory string) is a UTF-8 encoded string
representing the name of the authentication realm
inside the authentication domain. As specified in
[I-D.ietf-httpbis-p7-auth], this value MUST always be
sent in the quoted-string form.
pwd-hash: (non-mandatory extensive-token) specifies the hash
algorithm (hereafter referred to by ph) used for
additionally hashing the password. The valid tokens
are
* none: ph(p) = p
* md5: ph(p) = MD5(p)
* digest-md5: ph(p) = MD5(username | ":" | realm |
":" | p), the same value as MD5(A1) for "MD5"
algorithm in [RFC2617].
* sha1: ph(p) = SHA1(p)
If omitted, the value "none" is assumed. The use of
"none" is recommended.
reason: (mandatory extensive-token) SHALL be an extensive-
token which describes the possible reason of the
failed authentication/authorization. Both servers and
clients SHALL understand and support the following
three tokens:
* initial: authentication was not tried because there
was no Authorization header in the corresponding
request.
* stale-session: the provided sid; in the request was
either unknown to or expired in the server.
* auth-failed: authentication trial was failed by
some reasons, possibly with a bad authentication
credentials.
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Implementations MAY support the following tokens or
any extensive-tokens defined outside this
specification. If clients has received any unknown
tokens, these SHOULD treat these as if it were "auth-
failed" or "initial".
* reauth-needed: server-side application requires a
new authentication trial, regardless of the current
status.
* invalid-parameters: authentication was not even
tried in the server-side because some parameters
are not acceptable.
* internal-error: authentication was not even tried
in the server-side because there is some troubles
on the server-side.
* user-unknown: a special case of auth-failed,
suggesting that the provided user-name is invalid.
The use of this parameter is NOT RECOMMENDED for
security implications, except for special-purpose
applications which makes this value sense.
* invalid-credential: ditto, suggesting that the
provided user-name was valid but authentication was
failed. The use of this parameter is
NOT RECOMMENDED as the same as the above.
The algorithm specified in this header will determine the types
(among those defined in Section 3) and the values for K_c1, K_s1,
VK_c and VK_s.
Among these messages, those with the reason parameter of value
"stale-session" will be called "401-STALE" messages hereafter,
because these have a special meaning in the protocol flow. Messages
with any other reason parameters will be called "401-INIT" messages.
4.2. req-KEX-C1
Every req-KEX-C1 message SHALL be a valid HTTP request message
containing an "Authorization" header with a credential containing a
"kc1" parameter.
The credential SHALL contain the parameters with the following names:
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version: (mandatory, extensive-token) should be the token
"-draft11" in this specification. The behavior is
undefined when other values are specified.
algorithm, validation, auth-domain, realm: MUST be the same value as
it is when received from the server.
user: (mandatory, string) is the UTF-8 encoded name of the
user. If this name comes from a user input, client
software SHOULD prepare the string using SASLprep
[RFC4013] before encoding it to UTF-8.
kc1: (mandatory, algorithm-determined) is the client-side
key exchange value K_c1, which is specified by the
algorithm that is used.
rekey-sid: (non-mandatory, hex-fixed-number): reserved for future
extensions (see rekey-method in "200-VFY-S" message).
4.3. 401-KEX-S1
Every 401-KEX-S1 message SHALL be a valid HTTP 401-status
(Authentication Required) response message containing a
"WWW-Authenticate" header with a challenge containing a "ks1"
parameter.
The challenge SHALL contain the parameters with the following names:
version: (mandatory, extensive-token) should be the token
"-draft11" in this specification. The behavior is
undefined when other values are specified.
algorithm, validation, auth-domain, realm: MUST be the same value as
it is when received from the client.
sid: (mandatory, hex-fixed-number) MUST be a session
identifier, which is a random integer. The sid SHOULD
have uniqueness of at least 80 bits or the square of
the maximal estimated transactions concurrently
available in the session table, whichever is larger.
See Section 6 for more details.
ks1: (mandatory, algorithm-determined) is the server-side
key exchange value K_s1, which is specified by the
algorithm.
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nc-max: (mandatory, integer) is the maximal value of nonce
counts that the server accepts.
nc-window: (mandatory, integer) the number of available nonce
slots that the server will accept. The value of the
nc-window parameter is RECOMMENDED to be 32 or more.
time: (mandatory, integer) represents the suggested time (in
seconds) that the client can reuse the session
represented by the sid. It is RECOMMENDED to be at
least 60. The value of this parameter is not directly
linked to the duration that the server keeps track of
the session represented by the sid.
path: (non-mandatory, string) specifies which path in the
URI space the same authentication is expected to be
applied. The value is a space-separated list of URIs,
in the same format as it was specified in domain
parameter [RFC2617] for the Digest authentications,
and clients are RECOMMENDED to recognize it. The all
path elements contained in the parameter MUST be
inside the specified auth-domain: if not, clients
SHOULD ignore such elements.
4.4. req-VFY-C
Every req-VFY-C message SHALL be a valid HTTP request message
containing an "Authorization" header with a credential containing a
"vkc" parameter.
The parameters contained in the header are as follows:
version: (mandatory, extensive-token) should be the token
"-draft11" in this specification. The behavior is
undefined when other values are specified.
algorithm, validation, auth-domain, realm: MUST be the same value as
it is when received from the server for the session.
sid: (mandatory, hex-fixed-number) MUST be one of the sid
values that was received from the server for the same
authentication realm.
nc: (mandatory, integer) is a nonce value that is unique
among the requests sharing the same sid. The values
of the nonces SHOULD satisfy the properties outlined
in Section 6.
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vkc: (mandatory, algorithm-determined) is the client-side
authentication verification value VK_c, which is
specified by the algorithm.
4.5. 200-VFY-S
Every 200-VFY-S message SHALL be a valid HTTP message that is not of
the 401 (Authentication Required) status, containing an
"Authentication-Info" header with a "vks" parameter.
The parameters contained in the header are as follows:
version: (mandatory, extensive-token) should be the token
"-draft11" in this specification. The behavior is
undefined when other values are specified.
sid: (mandatory, hex-fixed-number) MUST be the value
received from the client.
vks: (mandatory, algorithm-determined) is the server-side
authentication verification value VK_s, which is
specified by the algorithm.
logout-timeout: (non-mandatory, integer) is the number of seconds
after which the client should re-validate the user's
password for the current authentication realm. The
value 0 means that the client SHOULD automatically
forget the user-inputted password for the current
authentication realm and revert to the unauthenticated
state (i.e. server-initiated logout). This does not,
however, mean that the long-term memories for the
passwords (such as the password reminders and auto
fill-ins) should be removed. If a new timeout value
is received for the same authentication realm, it
overrides the previous timeout. If logout-timeout
parameters are specified both in an
Authentication-Info header and an
Authentication-Control header
([I-D.oiwa-http-auth-extension]), the client SHOULD
respect the smaller one of those and ignore the other.
rekey-method: (non-mandatory, extensive-token): defining a
credential used for reestablishing a new session with
a new sid. It must be either omitted or the token
"passwords" at the current specification. The bare-
tokens "refresh-key" and "refresh-key-global" are
reserved for future extensions.
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The header MUST be sent before the content body: it MUST NOT be sent
in the trailer of a chunked-encoded response. If a "100 Continue"
response is sent from the server, the Authentication-Info header
SHOULD be included in that response, instead of the final response.
5. Authentication Realms
In this protocol, an "authentication realm" is defined as a set of
resources (URIs) for which the same set of user names and passwords
is valid for. If the server requests authentication for an
authentication realm that the client is already authenticated for,
the client will automatically perform the authentication using the
already-known secrets. However, for the different authentication
realms, the clients SHOULD NOT automatically reuse the usernames and
passwords for another realm.
Just like in Basic and Digest access authentication protocols, Mutual
authentication protocol supports multiple, separate protection spaces
to be set up inside each host. Furthermore, the protocol supports
that a single authentication realm spans over several hosts within
the same Internet domain.
Each authentication realm is defined and distinguished by the triple
of an "authentication algorithm", an "authentication domain", and a
"realm" parameter. However, server operators are NOT RECOMMENDED to
use the same pair of an authentication domain and a realm for
different authentication algorithms.
The realm parameter is a string as defined in Section 4.
Authentication domains are described in the remainder of this
section.
An authentication domain specifies the range of hosts that the
authentication realm spans over. In this protocol, it MUST be one of
the following strings.
o Single-server type: The string in format
"<scheme>://<host>:<port>", where <scheme>, <host>, and <port> are
the corresponding URI parts of the request URI. Even if the
request-URI does not have a port part, the string will include one
(i.e. 80 for http and 443 for https). The port part MUST NOT
contain leading zeros. Use this when authentication is only valid
for specific protocol (such as https).
o Single-host type: The "host" part of the requested URI. This is
the default value. Authentication realms within this kind of
authentication domain will span over several protocols (i.e. http
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and https) and ports, but not over different hosts.
o Wildcard-domain type: The string in format "*.<domain-postfix>",
where <domain-postfix> is either the host part of the requested
URI or any domain in which the requested host is included (this
means that the specification "*.example.com" is valid for all of
hosts "www.example.com", "web.example.com",
"www.sales.example.com" and "example.com"). The domain-postfix
sent from the servers MUST be equal to or included in a valid
Internet domain assigned to a specific organization: if clients
know, by some means such as a blacklist for HTTP cookies
[RFC6265], that the specified domain is not to be assigned to any
specific organization (e.g. "*.com" or "*.jp"), the clients are
RECOMMENDED to reject the authentication request.
In the above specifications, every "scheme", "host", and "domain"
MUST be in lower-case, and any internationalized domain names beyond
the ASCII character set SHALL be represented in the way they are sent
in the underlying HTTP protocol, represented in lower-case
characters; i.e. these SHALL be in the form of the LDH labels in IDNA
[RFC5890]. All "port"s MUST be in the shortest, unsigned, decimal
number notation. Not obeying these requirements will cause failure
of valid authentication attempts.
5.1. Resolving Ambiguities
In the above definitions of authentication domains, several domains
will overlap each other. Depending on the "path" parameters given in
the "401-KEX-S1" message (see Section 4), there may be several
candidates when the client is going to send a request including an
authentication credential (Steps 3 and 4 of the decision procedure
presented in Section 9).
If such choices are required, the following procedure SHOULD be
followed.
o If the client has previously sent a request to the same URI, and
if it remembers the authentication realm requested by 401-INIT
messages at that time, use that realm.
o In other cases, use one of authentication realms representing the
most-specific authentication domains. From the list of possible
domain specifications shown above, each one earlier has priority
over ones described after that.
If there are several choices with different domain-postfix
specifications, the one that has the longest domain-postfix has
priority over ones with a shorter domain-postfix.
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o If there are realms with the same authentication domain, there is
no defined priority: the client MAY choose any one of the possible
choices.
If possible, server operators are encouraged to avoid such
ambiguities by properly setting the "path" parameters.
6. Session Management
In the Mutual authentication protocol, a session represented by an
sid is set up using first four messages (first request, 401-INIT,
req-KEX-C1 and 401-KEX-S1), and a "session secret" (z) associated
with the session is established. After sharing a session secret,
this session, along with the secret, can be used for one or more
requests for resources protected by the same realm in the same
server. Note that session management is only an inside detail of the
protocol and usually not visible to normal users. If a session
expires, the client and server SHOULD automatically reestablish
another session without informing the users.
Sessions and session identifiers are local to each server (defined by
scheme, host and port) inside an authentication domain; the clients
MUST establish separate sessions for each port of a host to be
accessed. Furthermore, sessions and identifiers are also local to
each authentication realm, even if these are provided from the same
servers. The same session identifiers provided either from different
servers or for different realms SHOULD be treated as independent
ones.
The server SHOULD accept at least one req-VFY-C request for each
session, given that the request reaches the server in a time window
specified by the timeout parameter in the 401-KEX-S1 message, and
that there are no emergent reasons (such as flooding attacks) to
forget the sessions. After that, the server MAY discard any session
at any time and MAY send 401-STALE messages for any req-VFY-C
requests.
The client MAY send two or more requests using a single session
specified by the sid. However, for all such requests, each value of
the nonce (in the nc parameter) MUST satisfy the following
conditions:
o It is a natural number.
o The same nonce was not sent within the same session.
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o It is not larger than the nc-max value that was sent from the
server in the session represented by the sid.
o It is larger than (largest-nc - nc-window), where largest-nc is
the maximal value of nc which was previously sent in the session,
and nc-window is the value of the nc-window parameter which was
received from the server in the session.
The last condition allows servers to reject any nonce values that are
"significantly" smaller than the "current" value (defined by the
value of nc-window) of the nonce used in the session involved. In
other words, servers MAY treat such nonces as "already received".
This restriction enables servers to implement duplicated nonce
detection in a constant amount of memory (for each session).
Servers MUST check for duplication of the received nonces, and if any
duplication is detected, the server MUST discard the session and
respond with a 401-STALE message, as outlined in Section 10. The
server MAY also reject other invalid nonce values (such as ones above
the nc-max limit) by sending a 401-STALE message.
For example, assume the nc-window value of the current session is 32,
nc-max is 100, and that the client has already used the following
nonce values: {1-20, 22, 24, 30-38, 45-60, 63-72}. Then the nonce
values that can be used for next request is one of the following set:
{41-44, 61-62, 73-100}. The values {0, 21, 23, 25-29, 39-40} MAY be
rejected by the server because they are not above the current "window
limit" (40 = 72 - 32).
Typically, clients can ensure the above property by using a
monotonically-increasing integer counter that counts from zero upto
the value of nc-max.
The values of the nonces and any nonce-related values MUST always be
treated as natural numbers within an infinite range. Implementations
using fixed-width integers or fixed-precision floating numbers MUST
correctly and carefully handle integer overflows. Such
implementations are RECOMMENDED to accept any larger values that
cannot be represented in the fixed-width integer representations, as
long as other limits such as internal header-length restrictions are
not involved. The protocol is designed carefully so that both the
clients and servers can implement the protocol using only fixed-width
integers, by rounding any overflowed values to the maximum possible
value.
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7. Validation Methods
The "validation method" specifies a method to "relate" the mutual
authentication processed by this protocol with other authentications
already performed in the underlying layers and to prevent man-in-the-
middle attacks. It decides the value v that is an input to the
authentication protocols.
The valid tokens for the validation parameter and corresponding
values of v are as follows:
host: hostname validation: The value v will be the ASCII
string in the following format:
"<scheme>://<host>:<port>", where <scheme>, <host>,
and <port> are the URI components corresponding to the
currently accessing resource. The scheme and host are
in lower-case, and the port is in a shortest decimal
representation. Even if the request-URI does not have
a port part, v will include one.
tls-cert: TLS certificate validation: The value v will be the
octet string of the hash value of the public key
certificate used in the underlying TLS [RFC5246] (or
SSL) connection. The hash value is defined as the
value of the entire signed certificate (specified as
"Certificate" in [RFC5280]), hashed by the hash
algorithm specified by the authentication algorithm
used.
tls-key: TLS shared-key validation: The value v will be the
octet string of the shared master secret negotiated in
the underlying TLS (or SSL) connection.
If the HTTP protocol is used on a non-encrypted channel (TCP and
SCTP, for example), the validation type MUST be "host". If HTTP/TLS
[RFC2818] (HTTPS) protocol is used with the server certificates, the
validation type MUST be either "tls-cert" or "tls-key". If HTTP/TLS
protocol is used with an anonymous Diffie-Hellman key exchange, the
validation type MUST be "tls-key" (see the note below).
If the validation type "tls-cert" is used, the server certificate
provided on TLS connection MUST be verified to make sure that the
server actually owns the corresponding secret key.
Clients MUST validate this parameter upon reception of the 401-INIT
messages.
However, when the client is a Web browser with any scripting
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capabilities, the underlying TLS channel used with HTTP/TLS MUST
provide server identity verification. This means (1) the anonymous
Diffie-Hellman key exchange ciphersuite MUST NOT be used, and (2) the
verification of the server certificate provided from the server MUST
be performed.
For other systems, when the underlying TLS channel used with HTTP/TLS
does not perform server identity verification, the client SHOULD
ensure that all the responses are validated using the Mutual
authentication protocol, regardless of the existence of the 401-INIT
responses.
Note: The protocol defines two variants for validation on the TLS
connections. The "tls-key" method is more secure. However, there
are some situations where tls-cert is more preferable.
o When TLS accelerating proxies are used, it is difficult for the
authenticating server to acquire the TLS key information that is
used between the client and the proxy. This is not the case for
client-side "tunneling" proxies using a CONNECT method extension
of HTTP.
o When a black-box implementation of the TLS protocol is used on
either peer.
Implementations supporting a Mutual authentication over the HTTPS
protocol SHOULD support the "tls-cert" validation. Support for
"tls-key" validation is OPTIONAL for both the servers and clients.
8. Authentication Extensions
The HTTP authentication extensions described in
[I-D.oiwa-http-auth-extension] is a definitive part of this protocol.
Interactive clients (e.g. Web browsers) supporting this protocol are
RECOMMENDED to support non-mandatory authentication and the
Authentication-Control header defined there, except the "auth-style"
parameter. This specification also proposes (however, not mandates)
default "auth-style" to be "non-modal". Web applications SHOULD
however consider the security impacts of the behaviors of clients
that do not support these headers.
Authentication-initializing messages with the
Optional-WWW-Authenticate header are used where 401-INIT response is
valid. Such a message is called a 200-Optional-INIT message in this
document. (It will not replace other 401-type messages such as
401-STALE and 401-KEX-S1.)
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9. Decision Procedure for Clients
To securely implement the protocol, the user client must be careful
about accepting the authenticated responses from the server. This
also holds true for the reception of "normal responses" (responses
which do not contain Mutual-related headers) from HTTP servers.
Clients SHOULD implement a decision procedure equivalent to the one
shown below. (Unless implementers understand what is required for
the security, they should not alter this.) In particular, clients
SHOULD NOT accept "normal responses" unless explicitly allowed below.
The labels on the steps are for informational purposes only. Action
entries within each step are checked in top-to-bottom order, and the
first clause satisfied SHOULD be taken.
Step 1 (step_new_request):
If the client software needs to access a new Web resource, check
whether the resource is expected to be inside some authentication
realm for which the user has already been authenticated by the
Mutual authentication scheme. If yes, go to Step 2. Otherwise,
go to Step 5.
Step 2:
Check whether there is an available sid for the authentication
realm you expect. If there is one, go to Step 3. Otherwise, go
to Step 4.
Step 3 (step_send_vfy_1):
Send a req-VFY-C request.
* If you receive a 401-INIT message with a different
authentication realm than expected, go to Step 6.
* If you receive a 200-Optional-INIT message with a different
authentication realm than expected, go to Step 6.
* If you receive a 401-STALE message, go to Step 9.
* If you receive a 401-INIT message, go to Step 13.
* If you receive a 200-VFY-S message, go to Step 14.
* If you receive a normal response, go to Step 11.
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Step 4 (step_send_kex1_1):
Send a req-KEX-C1 request.
* If you receive a 401-INIT message with a different
authentication realm than expected, go to Step 6.
* If you receive a 200-Optional-INIT message with a different
authentication realm than expected, go to Step 6.
* If you receive a 401-KEX-S1 message, go to Step 10.
* If you receive a 401-INIT message with the same authentication
realm, go to Step 13 (see Note 1).
* If you receive a normal response, go to Step 11.
Step 5 (step_send_normal_1):
Send a request without any Mutual authentication headers.
* If you receive a 401-INIT message, go to Step 6.
* If you receive a 200-Optional-INIT message, go to Step 6.
* If you receive a normal response, go to Step 11.
Step 6 (step_rcvd_init):
Check whether you know the user's password for the requested
authentication realm. If yes, go to Step 7. Otherwise, go to
Step 12.
Step 7:
Check whether there is an available sid for the authentication
realm you expect. If there is one, go to Step 8. Otherwise, go
to Step 9.
Step 8 (step_send_vfy):
Send a req-VFY-C request.
* If you receive a 401-STALE message, go to Step 9.
* If you receive a 401-INIT message, go to Step 13.
* If you receive a 200-VFY-S message, go to Step 14.
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Step 9 (step_send_kex1):
Send a req-KEX-C1 request.
* If you receive a 401-KEX-S1 message, go to Step 10.
* If you receive a 401-INIT message, go to Step 13 (See Note 1).
Step 10 (step_rcvd_kex1):
Send a req-VFY-C request.
* If you receive a 401-INIT message, go to Step 13.
* If you receive a 200-VFY-S message, go to Step 14.
Step 11 (step_rcvd_normal):
The requested resource is out of the authenticated area. The
client will be in the "UNAUTHENTICATED" status. If the response
contains a request for authentications other than Mutual, it MAY
be handled normally.
Step 12 (step_rcvd_init_unknown):
The requested resource requires a Mutual authentication, and the
user is not yet authenticated. The client will be in the "AUTH-
REQUESTED" status, and is RECOMMENDED to process the content sent
from the server, and to ask user for a user name and a password.
When those are supplied from the user, proceed to Step 9.
Step 13 (step_rcvd_init_failed):
For some reason the authentication failed: possibly the password
or the username is invalid for the authenticated resource.
Forget the password for the authentication realm and go to Step
12.
Step 14 (step_rcvd_vfy):
Check the validity of the received VK_s value. If it is equal to
the expected value, it means that the mutual authentication has
succeeded. The client will be in the "AUTH-SUCCEEDED" status.
If the value is unexpected, it is a fatal communication error.
If a user explicitly requests to log out (via user interfaces),
the client MUST forget the user's password, go to step 5 and
reload the current resource without an authentication header.
Note 1: These transitions MAY be accepted by clients, but
NOT RECOMMENDED for servers to initiate.
Any kind of response (including a normal response) other than those
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shown in the above procedure SHOULD be interpreted as a fatal
communication error, and in such cases the clients MUST NOT process
any data (response body and other content-related headers) sent from
the server. However, to handle exceptional error cases, clients MAY
accept a message without an Authentication-Info header, if it is a
Server-Error (5xx) status. The client will be in the
"UNAUTHENTICATED" status in these cases.
The client software SHOULD display the three client status to the
end-user. For an interactive client, however, if a request is a sub-
request for a resource included in another page (e.g., embedded
images, style sheets, frames etc.), its status MAY be omitted from
being shown, and any "AUTH-REQUESTED" statuses MAY be treated in the
same way as an "UNAUTHENTICATED" status.
Figure 5 shows a diagram of the client-side state.
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=========== -(11)------------
NEW REQUEST ( UNAUTHENTICATED )
=========== -----------------
| ^ normal
v | response
+(1)-------------------+ NO +(5)----------+
| The requested URI |--------------------------->| send normal |
| known to be auth'ed? | | request |
+----------------------+ +-------------+
YES | 401-INIT, 200-Optional-INIT 401-INIT|
| with a different realm 200-Optional-INIT|
| -----------------------------------. |
| / v v
| | -(12)------------ NO +(6)--------+
| | ( AUTH-REQUESTED )<------| user/pass |
| | ----------------- | known? |
| | +-----------+
| | |YES
v | v
+(2)--------+ | +(7)--------+
| session | | | session | NO
NO /| available?| | | available?|\
/ +-----------+ | +-----------+ |
/ |YES | |YES |
| | /| | |
| v / | 401- 401- v |
| +(3)--------+ | INIT --(13)---------- INIT +(8)--------+ |
| | send |--+----->/ AUTH-REQUESTED \<-------| send | |
| /| req-VFY-C | | \forget password / | req-VFY-C | |
\/ +-----------+ / ---------------- /+-----------+ |
/\ \ \/ ^ 401-INIT | |401- |
| ------ \/\ 401-STALE | | | STALE /
| \ /\ -----------------+--------------+---. | /
| | / \ | | | | /
| v / | 401- | 401- | v v v
| +(4)--------+ | KEX-S1 +(10)-------+ KEX-S1 | +(9)--------+
| | send |-|--------->| send |<-------+-| send |
| --| req-KEX-C1| | | req-VFY-C | | | req-KEX-C1|
|/ +-----------+ | +-----------+ | +-----------+
| |200-VFY-S | 200-VFY-S| ^
|normal | |200-VFY-S / |
|response | v / ==================
v \ -(14)--------- / USER/PASS INPUTTED
-(11)------------ ------->( AUTH-SUCCEED )<-- ==================
( UNAUTHENTICATED ) --------------
-----------------
Figure 5: State diagram for clients
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10. Decision Procedure for Servers
Each server SHOULD have a table of session states. This table need
not be persistent over a long term; it MAY be cleared upon server
restart, reboot, or others. Each entry in the table SHOULD contain
at least the following information:
o The session identifier, the value of the sid parameter.
o The algorithm used.
o The authentication realm.
o The state of the protocol: one of "key exchanging",
"authenticated", "rejected", or "inactive".
o The user name received from the client
o The boolean flag noting whether or not the session is fake.
o When the state is "key exchanging", the values of K_c1 and S_s1.
o When the state is "authenticated", the following information:
* The value of the session secret z
* The largest nc received from the client (largest-nc)
* For each possible nc values between (largest-nc - nc-
window + 1) and max_nc, a flag whether or not a request with
the corresponding nc has been received.
The table MAY contain other information.
Servers SHOULD respond to the client requests according to the
following procedure:
o When the server receives a normal request:
* If the requested resource is not protected by the Mutual
Authentication, send a normal response.
* If the resource is protected by the Mutual Authentication, send
a 401-INIT response.
* If the resource is protected by the optional Mutual
Authentication, send a 200-Optional-INIT response.
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o When the server receives a req-KEX-C1 request:
* If the requested resource is not protected by the Mutual
Authentication, send a normal response.
* If the authentication realm specified in the req-KEX-C1 request
is not the expected one, send either a 401-INIT or a
200-Optional-INIT response.
* If the server cannot validate the parameter kc1, send a
401-INIT response.
* If the received user name is either invalid, unknown or
unacceptable, create a new session, mark it a "fake" session,
compute a random value as K_s1, and send a fake 401-KEX-S1
response. (Note: the server SHOULD NOT send a 401-INIT
response in this case, because it will leak the information to
the client that the specified user will not be accepted.
Instead, postpone it to the response for the next req-VFY-C
request.)
* Otherwise, create a new session, compute K_s1 and send a
401-KEX-S1 response.
The created session has the "key exchanging" state.
o When the server receives a req-VFY-C request:
* If the requested resource is not protected by the Mutual
Authentication, send a normal response.
* If the authentication realm specified in the req-VFY-C request
is not the expected one, send either a 401-INIT or a
200-Optional-INIT response.
If none of above holds true, the server will lookup the session
corresponding to the received sid and the authentication realm.
* If the session corresponding to the received sid could not be
found, or it is in the "inactive" state, send a 401-STALE
response.
* If the session is in the "rejected" state, send either a
401-INIT or a 401-STALE message.
* If the session is in the "authenticated" state, and the request
has an nc value that was previously received from the client,
send a 401-STALE message. The session SHOULD be changed to the
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"inactive" status.
* If the nc value in the request is larger than the nc-max
parameter sent from the server, or if it is not larger then
(largest-nc - nc-window) (when in "authenticated" status), the
server MAY (but not REQUIRED to) send a 401-STALE message. The
session SHOULD be changed to the "inactive" status if so.
* If the session is a "fake" session, or if the received vkc is
incorrect, then send a 401-INIT response. If the session is in
the "key exchanging" state, it SHOULD be changed to the
"rejected" state; otherwise, it MAY either be changed to the
"rejected" status or kept in the previous state.
* Otherwise, send a 200-VFY-S response. If the session was in
the "key exchanging" state, the session SHOULD be changed to an
"authenticated" state. The maximum nc and nc flags of the
state SHOULD be updated properly.
At any time, the server MAY change any state entries with both the
"rejected" and "authenticated" statuses to the "inactive" status, and
MAY discard any "inactive" states from the table. The entries with
the "key exchanging" status SHOULD be kept unless there is an
emergency situation such as a server reboot or a table capacity
overflow.
11. Authentication Algorithms
Cryptographic authentication algorithms which are used with this
protocol will be defined separately. The algorithm definition MUST
at least provide a definitions for the following functions:
o The server-side authentication credential J, derived from user-
side authentication credential pi.
o Key exchange values K_c1, K_s1 (exchanged on wire) and S_c1, S_s1
(kept secret in each peer).
o Shared secret z, to be computed in both server-side and client
side.
o A hash function H to be used with the protocol.
All algorithm used with this protocol SHOULD provide secure mutual
authentication between client and servers, and generate a
cryptographically strong shared secret value z, equivalently strong
to or stronger than the hash function H. If any passwords (or pass-
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phrases or any equivalents, i.e. weak secrets) are involved, these
SHOULD NOT be guessable from any data transmitted in the protocol,
even if an attacker (either an eavesdropper or an active server)
knows the possible thoroughly-searchable candidate list of the
passwords. Furthermore, if possible, the function for deriving
server-side authentication credential J is RECOMMENDED to be one-way
so that pi should not be easily computed from J(pi).
11.1. Support Functions and Notations
In this section we define several support functions and notations to
be shared by several algorithm definitions:
The integers in the specification are in decimal, or in hexadecimal
when prefixed with "0x".
The function octet(c) generates a single octet string whose code
value is equal to c. The operator |, when applied to octet strings,
denotes the concatenation of two operands.
The function VI encodes natural numbers into octet strings in the
following manner: numbers are represented in big-endian radix-128
string, where each digit is represented by a octet within 0x80-0xff
except the last digit represented by a octet within 0x00-0x7f. The
first octet MUST NOT be 0x80. For example, VI(i) = octet(i) for i <
128, and VI(i) = octet(0x80 + (i >> 7)) | octet(i & 127) for 128 <= i
< 16384. This encoding is the same as the one used for the
subcomponents of object identifiers in the ASN.1 encoding
[ITU.X690.1994], and available as a "w" conversion in the pack
function of several scripting languages.
The function VS encodes a variable-length octet string into a
uniquely-decoded, self-delimited octet string, as in the following
manner:
VS(s) = VI(length(s)) | s
where length(s) is a number of octets (not characters) in s.
Some examples:
VI(0) = "000円" (in C string notation)
VI(100) = "d"
VI(10000) = "316円020円"
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VI(1000000) = "275円204円@"
VS("") = "000円"
VS("Tea") = "003円Tea"
VS("Caf<e acute>" [in UTF-8]) = "005円Caf303円251円"
VS([10000 "a"s]) = "316円020円aaaaa..." (10002 octets)
[Editorial note: Unlike the colon-separated notion used in the Basic/
Digest HTTP authentication scheme, the string generated by a
concatenation of the VS-encoded strings will be unique, regardless of
the characters included in the strings to be encoded.]
The function OCTETS converts an integer into the corresponding radix-
256 big-endian octet string having its natural length: See
Section 3.1.3 for the definition of "natural length".
11.2. Default Functions for Algorithms
The functions defined in this section are common default functions
among authentication algorithms.
The client-side password-based string pi used by this authentication
is derived in the following manner:
pi = H(VS(algorithm) | VS(auth-domain) | VS(realm) | VS(username) |
VS(ph(password))).
The values of algorithm, realm, and auth-domain are taken from the
values contained in the 401-INIT (or 200-Optional-INIT, hereafter
implied) message. When pi is used in the context of an octet string,
it SHALL have the natural length derived from the size of the output
of function H (e.g. 32 octets for SHA-256). The function ph is
determined by the value of the pwd-hash parameter given in a 401-INIT
message. If the password comes from a user input, it SHOULD first be
prepared using SASLprep [RFC4013]. Then, the password SHALL be
encoded as a UTF-8 string before passed to ph.
The values VK_c and VK_s are derived by the following equation.
VK_c = H(octet(4) | OCTETS(K_c1) | OCTETS(K_s1) | OCTETS(z) | VI(nc)
| VS(v))
VK_s = H(octet(3) | OCTETS(K_c1) | OCTETS(K_s1) | OCTETS(z) | VI(nc)
| VS(v))
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Specifications for cryptographic algorithms used with this framework
MAY override the functions pi, VK_c, and VK_s defined above. In such
cases implementations MUST use the ones defined with such algorithm
specifications.
12. Application Channel Binding
Applications and upper-layer communication protocols may need
authentication binding to the HTTP-layer authenticated user. Such
applications MAY use the following values as a standard shared
secret.
These values are parameterized with an optional octet string (t)
which may be arbitrarily chosen by each applications or protocols.
If there is no appropriate value to be specified, use a null string
for t.
For applications requiring binding to either an authenticated user or
a shared-key session (to ensure that the requesting client is
certainly authenticated), the following value b_1 MAY be used.
b_1 = OCTETS(H(OCTETS(H(octet(6) | OCTETS(K_c1) | OCTETS(K_s1) |
OCTETS(z) | VI(0) | VS(v))) | VS(t))).
For applications requiring binding to a specific request (to ensure
that the payload data is generated for the exact HTTP request), the
following value b_2 MAY be used.
b_2 = OCTETS(H(OCTETS(H(octet(7) | OCTETS(K_c1) | OCTETS(K_s1) |
OCTETS(z) | VI(nc) | VS(v))) | VS(t))).
Note: Channel bindings to lower-layer transports (TCP and TLS) are
defined in Section 7.
13. Application for Proxy Authentication
The authentication scheme defined by the previous sections can be
applied m.m. for proxy authentications. In such cases, the following
alterations MUST be applied:
o The 407 status is to be sent and recognized for places where the
401 status is used,
o Proxy-Authenticate: header is to be used for places where WWW-
Authenticate: is used,
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o Proxy-Authorization: header is to be used for places where
Authorization: is used,
o Proxy-Authentication-Info: header is to be used for places where
Authentication-Info: is used,
o The auth-domain parameter is fixed to the host-name of the proxy,
which means to cover all requests processed through the specific
proxy,
o The limitation for the paths contained in the path parameter of
401-KEX-S1 messages is disregarded,
o The omission of the path parameter of 401-KEX-S1 messages means
that the authentication realm will potentially cover all requests
processed by the proxy,
o The scheme, host name and the port of the proxy is used for
validation tokens, and
o Authentication extension in [I-D.oiwa-http-auth-extension] is not
applicable.
The requirements for client software to display the authentication
status to the end-user is also not applicable for proxy
authentication. If the client software supports both end-to-end and
proxy authentication using this protocol, it SHOULD be careful that
the authentication status of the proxy communication will never be
confused by users with authentication statuses of the end-to-end
resource authentications.
14. Methods to Extend This Protocol
If a private extension to this protocol is implemented, it MUST use
the extension-tokens defined in Section 3 to avoid conflicts with
this protocol and other extensions. (standardized or being-
standardizing extensions MAY use either bare-tokens or extension-
tokens.)
Specifications defining authentication algorithms MAY use other
representations for the parameters "kc1", "ks1", "vkc", and "vks",
replace those parameter names, and/or add parameters to the messages
containing those parameters in supplemental specifications, provided
that syntactic and semantic requirements in Section 3,
[I-D.ietf-httpbis-p1-messaging] and [I-D.ietf-httpbis-p7-auth] are
satisfied. Any parameters starting with "kc", "ks", "vkc" or "vks"
and followed by decimal natural numbers (e.g. kc2, ks0, vkc1, vks3
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etc.) are reserved for this purpose. If those specifications use
names other than those mentioned above, it is RECOMMENDED to use
extension-tokens to avoid any parameter name conflict with the future
extension of this protocol.
Extension-tokens MAY be freely used for any non-standard, private,
and/or experimental uses for those parameters provided that the
domain part in the token is appropriately used.
15. IANA Considerations
When bare-tokens are used for the authentication-algorithm, pwd-hash,
and validation parameters MUST be allocated by IANA. To acquire
registered tokens, a specification for the use of such tokens MUST be
available as an RFC, as outlined in [RFC5226].
Note: More formal declarations will be added in the future drafts to
meet the RFC 5226 requirements.
16. Security Considerations
16.1. Security Properties
o The protocol is secure against passive eavesdropping and replay
attacks. However, the protocol relies on transport security
including DNS integrity for data secrecy and integrity. HTTP/TLS
SHOULD be used where transport security is not assured and/or data
secrecy is important.
o When used with HTTP/TLS, if TLS server certificates are reliably
verified, the protocol provides true protection against active
man-in-the-middle attacks.
o Even if the server certificate is not used or is unreliable, the
protocol provides protection against active man-in-the-middle
attacks for each HTTP request/response pair. However, in such
cases, JavaScript or similar scripting facilities can be used to
affect the Mutually-authenticated contents from other contents not
protected by this authentication mechanism. This is the reason
why this protocol requires that valid TLS server certificates MUST
be presented (Section 7).
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16.2. Denial-of-service Attacks to Servers
The protocol requires a server-side table of active sessions, which
may become a critical point of the server resource consumptions. For
proper operation, the protocol requires that at least one key
verification request is processed for each session identifier. After
that, servers MAY discard sessions internally at any time, without
causing any operational problems to clients. Clients will silently
reestablishes a new session then.
However, if a malicious client sends too many requests of key
exchanges (req-KEX-C1 messages) only, resource starvation might
occur. In such critical situations, servers MAY discard any kind of
existing sessions regardless of these statuses. One way to mitigate
such attacks are that servers MAY have a number and a time limits for
unverified pending key exchange requests (in the "wa received"
status).
This is a common weakness of authentication protocols with almost any
kind of negotiations or states, including Digest authentication
method and most Cookie-based authentication implementations.
However, regarding the resource consumption, a situation of the
mutual authentication method is a slightly better than the Digest,
because HTTP requests without any kind of authentication requests
will not generate any kind of sessions. Session identifiers are only
generated after a client starts a key negotiation. It means that
simple clients such as web crawlers will not accidentally consume
server-side resources for session managements.
16.3. Implementation Considerations
o To securely implement the protocol, the Authentication-Info
headers in the 200-VFY-S messages MUST always be validated by the
client. If the validation fails, the client MUST NOT process any
content sent with the message, including other headers and the
body part. Non-compliance to this requirement will allow phishing
attacks.
o The authentication status on the client-side SHOULD be visible to
the users of the client. In addition, the method for asking for
the user's name and passwords SHOULD be carefully designed so that
(1) the user can easily distinguish the request from this
authentication method from any other authentication methods such
as Basic and Digest methods, and (2) the Web contents cannot
imitate the user-interfaces for this protocol.
An informational memo regarding user-interface considerations and
recommendations for implementing this protocol will be separately
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published.
o For HTTP/TLS communications, when a web form is submitted from
Mutually-authenticated pages with the "tls-cert" validation method
to a URI that is protected by the same realm (so indicated by the
path parameter), if the server certificate has been changed since
the pages were received, the peer is RECOMMENDED to be revalidated
using a req-KEX-C1 message with an "Expect: 100-continue" header.
The same applies when the page is received with the "tls-key"
validation method, and when the TLS session has expired.
o Server-side storages of user passwords are advised to contain the
values encrypted by one-way function J(pi), instead of the real
passwords, those hashed by ph, or pi.
16.4. Usage Considerations
o The user-names inputted by a user may be sent automatically to any
servers sharing the same auth-domain. This means that when host-
type auth-domain is used for authentication on an HTTPS site, and
when an HTTP server on the same host requests Mutual
authentication within the same realm, the client will send the
user-name in a clear text. If user-names have to be kept secret
against eavesdropping, the server must use full-scheme-type auth-
domain parameter. Contrarily, passwords are not exposed to
eavesdroppers even on HTTP requests.
o The "pwd-hash" parameter is only provided for backward
compatibility of password databases. The use of "none" function
is the most secure choice and is RECOMMENDED. If values other
than "none" are used, you MUST ensure that the hash values of the
passwords were not exposed to the public. Note that hashed
password databases for plain-text authentications are usually not
considered secret.
o If the server provides several ways for storing server-side
password secrets into the password database, it is advised to
store the values encrypted by using the one-way function J(pi),
instead of the real passwords, those hashed by ph, or pi.
17. Notice on Intellectual Properties
The National Institute of Advanced Industrial Science and Technology
(AIST) and Yahoo! Japan, Inc. has jointly submitted a patent
application on the protocol proposed in this documentation to the
Patent Office of Japan. The patent is intended to be open to any
implementors of this protocol and its variants under non-exclusive
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royalty-free manner. For the details of the patent application and
its status, please contact the author of this document.
The elliptic-curve based authentication algorithms might involve
several existing third-party patents. The authors of the document
take no position regarding the validity or scope of such patents, and
other patents as well.
18. References
18.1. Normative References
[I-D.ietf-httpbis-p1-messaging]
Fielding, R., Lafon, Y., and J. Reschke, "HTTP/1.1, part
1: URIs, Connections, and Message Parsing",
draft-ietf-httpbis-p1-messaging-19 (work in progress),
March 2012.
[I-D.ietf-httpbis-p7-auth]
Fielding, R., Lafon, Y., and J. Reschke, "HTTP/1.1, part
7: Authentication", draft-ietf-httpbis-p7-auth-19 (work in
progress), March 2012.
[I-D.oiwa-http-auth-extension]
Oiwa, Y., Watanabe, H., Takagi, H., Kihara, B., Hayashi,
T., and Y. Ioku, "HTTP Authentication Extensions for
Interactive Clients", draft-oiwa-http-auth-extension-01
(work in progress), May 2012.
[I-D.oiwa-http-mutualauth-algo]
Oiwa, Y., Watanabe, H., Takagi, H., Kihara, B., Hayashi,
T., and Y. Ioku, "Mutual Authentication Protocol for HTTP:
KAM3-based Cryptographic Algorithms",
draft-oiwa-http-mutualauth-algo-02 (work in progress),
May 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names
and Passwords", RFC 4013, February 2005.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
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[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
18.2. Informative References
[I-D.ietf-precis-framework]
Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
Preparation and Comparison of Internationalized Strings in
Application Protocols", draft-ietf-precis-framework-03
(work in progress), May 2012.
[ISO.10646-1.1993]
International Organization for Standardization,
"Information Technology - Universal Multiple-octet coded
Character Set (UCS) - Part 1: Architecture and Basic
Multilingual Plane", ISO Standard 10646-1, May 1993.
[ITU.X690.1994]
International Telecommunications Union, "Information
Technology - ASN.1 encoding rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690, 1994.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings
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for TLS", RFC 5929, July 2010.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
April 2011.
Appendix A. (Informative) Draft Remarks from Authors
The following items are currently under consideration for future
revisions by the authors.
o Whether to keep TLS-key validation or not.
o When keeping tls-key validation, whether to use "TLS channel
binding" [RFC5929] for "tls-key" verification (Section 7). Note
that existing TLS implementations should be considered to
determine this.
o Adopt [I-D.ietf-precis-framework] for replacing SASLprep
reference. Especially, use NFC canonicalization instead of NFKC.
o Adding test vectors for ensuring implementation correctness.
o Possibly adding a method for servers to detect availability of
Mutual authentication on client-side.
o Possible support for optional key renewal and cross-site federated
authentication.
Appendix B. (Informative) Draft Change Log
B.1. Changes in Revision 11
o Message syntax definition reverted to pre-07 style as httpbis-p1
and p7 now defines a precise rule for parameter value parsing.
o Replaced "stale" parameter with more infomative/extensive "reason"
parameter in 401-INIT and 401-STALE.
o Reserved "rekey-sid" and "rekey-method" parameters for future
extensions.
o Added descriptions for replacing/non-replacing existing
technologies.
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B.2. Changes in Revision 10
o The authentication extension parts (non-mandatory authentication
and authentication controls) are separated to yet another draft.
o The default auth-domain parameter is changed to the full scheme-
host-port syntax, which is consistent with usual HTTP
authentication framework behavior.
o Provision for application channel binding is added.
o Provision for proxy access authentication is added.
o Bug fix: syntax specification of sid parameter was wrong: it was
inconsistent with the type specified in the main text (the bug
introduced in -07 draft).
o Terminologies for headers are changed to be in harmony with
httpbis drafts (e.g. field to parameter).
o Syntax definitions are changed to use HTTP-extended ABNF syntax,
and only the header values are shown for header syntax, in harmony
with httpbis drafts.
o Names of parameters and corresponding mathematical values are now
renamed to more informative ones. The following list shows
correspondence between the new and the old names.
+------------+----------+-------------------------------------------+
| new name | old name | description |
+------------+----------+-------------------------------------------+
| S_c1, S_s1 | s_a, s_b | client/server-side secret randoms |
| K_c1, K_s1 | w_a, w_b | client/server-side exchanged key |
| | | components |
| kc1, ks1 | wa, wb | parameter names for those |
| VK_c, VK_s | o_a, o_b | client/server-side key verifiers |
| vkc, vks | oa, ob | parameter names for those |
| z | z | session secrets |
+------------+----------+-------------------------------------------+
B.3. Changes in Revision 09
o The (default) cryptographic algorithms are separated to another
draft.
o Names of the messages are changed to more informative ones than
before. The following is the correspondence table of those names:
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+-------------------+-----------------+-----------------------------+
| new name | old name | description |
+-------------------+-----------------+-----------------------------+
| 401-INIT | 401-B0 | initial response |
| 401-STALE | 401-B0-stale | session key expired |
| req-KEX-C1 | req-A1 | client->server key exchange |
| 401-KEX-S1 | 401-B1 | server->client key exchange |
| req-VFY-C | req-A3 | client->server auth. |
| | | verification |
| 200-VFY-S | 200-B4 | server->client auth. |
| | | verification |
| 200-Optional-INIT | 200-Optional-B0 | initial with non-mandatory |
| | | authentication |
+-------------------+-----------------+-----------------------------+
B.4. Changes in Revision 08
o The English text has been revised.
B.5. Changes in Revision 07
o Adapt to httpbis HTTP/1.1 drafts:
* Changed definition of extensive-token.
* LWSP continuation-line (%0D.0A.20) deprecated.
o To simplify the whole spec, the type of nonce-counter related
parameters are change from hex-integer to integer.
o Algorithm tokens are renamed to include names of hash algorithms.
o Clarified the session management, added details of server-side
protocol decisions.
o The whole draft was reorganized; introduction and overview has
been rewritten.
B.6. Changes in Revision 06
o Integrated Optional Mutual Authentication to the main part.
o Clarified the decision procedure for message recognitions.
o Clarified that a new authentication request for any sub-requests
in interactive clients may be silently discarded.
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o Typos and confusing phrases are fixed.
o Several "future considerations" are added.
B.7. Changes in Revision 05
o A new parameter called "version" is added for supporting future
incompatible changes with a single implementation. In the (first)
final specification its value will be changed to 1.
o A new header "Authentication-Control" is added for precise control
of application-level authentication behavior.
B.8. Changes in Revision 04
o Changed text of patent licenses: the phrase "once the protocol is
accepted as an Internet standard" is removed so that the sentence
also covers the draft versions of this protocol.
o The "tls-key" verification is now OPTIONAL.
o Several description fixes and clarifications.
B.9. Changes in Revision 03
o Wildcard domain specifications (e.g. "*.example.com") are allowed
for auth-domain parameters (Section 4.1).
o Specification of the "tls-cert" verification is updated
(incompatible change).
o State transitions fixed.
o Requirements for servers concerning w_a values are clarified.
o RFC references are updated.
B.10. Changes in Revision 02
o Auth-realm is extended to allow full-scheme type.
o A decision diagram for clients and decision procedures for servers
are added.
o 401-B1 and req-A3 messages are changed to contain authentication
realm information.
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o Bugs on equations for o_A and o_B are fixed.
o Detailed equations for the entire algorithm are included.
o Elliptic-curve algorithms are updated.
o Several clarifications and other minor updates.
B.11. Changes in Revision 01
o Several texts are rewritten for clarification.
o Added several security consideration clauses.
Authors' Addresses
Yutaka Oiwa
National Institute of Advanced Industrial Science and Technology
Research Institute for Secure Systems
Tsukuba Central 2
1-1-1 Umezono
Tsukuba-shi, Ibaraki
JP
Email: mutual-auth-contact-ml@aist.go.jp
Hajime Watanabe
National Institute of Advanced Industrial Science and Technology
Hiromitsu Takagi
National Institute of Advanced Industrial Science and Technology
Boku Kihara
Lepidum Co. Ltd.
#602, Village Sasazuka 3
1-30-3 Sasazuka
Shibuya-ku, Tokyo
JP
Tatsuya Hayashi
Lepidum Co. Ltd.
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Yuichi Ioku
Yahoo! Japan, Inc.
Midtown Tower
9-7-1 Akasaka
Minato-ku, Tokyo
JP
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