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 * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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 */

package java.security;

import java.io.*;

/**
 * <p> SignedObject is a class for the purpose of creating authentic
 * runtime objects whose integrity cannot be compromised without being
 * detected.
 *
 * <p> More specifically, a SignedObject contains another Serializable
 * object, the (to-be-)signed object and its signature.
 *
 * <p> The signed object is a "deep copy" (in serialized form) of an
 * original object. Once the copy is made, further manipulation of
 * the original object has no side effect on the copy.
 *
 * <p> The underlying signing algorithm is designated by the Signature
 * object passed to the constructor and the {@code verify} method.
 * A typical usage for signing is the following:
 *
 * <pre>{@code
 * Signature signingEngine = Signature.getInstance(algorithm,
 * provider);
 * SignedObject so = new SignedObject(myobject, signingKey,
 * signingEngine);
 * }</pre>
 *
 * <p> A typical usage for verification is the following (having
 * received SignedObject {@code so}):
 *
 * <pre>{@code
 * Signature verificationEngine =
 * Signature.getInstance(algorithm, provider);
 * if (so.verify(publickey, verificationEngine))
 * try {
 * Object myobj = so.getObject();
 * } catch (java.lang.ClassNotFoundException e) {};
 * }</pre>
 *
 * <p> Several points are worth noting. First, there is no need to
 * initialize the signing or verification engine, as it will be
 * re-initialized inside the constructor and the {@code verify}
 * method. Secondly, for verification to succeed, the specified
 * public key must be the public key corresponding to the private key
 * used to generate the SignedObject.
 *
 * <p> More importantly, for flexibility reasons, the
 * constructor and {@code verify} method allow for
 * customized signature engines, which can implement signature
 * algorithms that are not installed formally as part of a crypto
 * provider. However, it is crucial that the programmer writing the
 * verifier code be aware what {@code Signature} engine is being
 * used, as its own implementation of the {@code verify} method
 * is invoked to verify a signature. In other words, a malicious
 * {@code Signature} may choose to always return true on
 * verification in an attempt to bypass a security check.
 *
 * <p> The signature algorithm can be, among others, the NIST standard
 * DSA, using DSA and SHA-256. The algorithm is specified using the
 * same convention as that for signatures. The DSA algorithm using the
 * SHA-256 message digest algorithm can be specified, for example, as
 * "SHA256withDSA". In the case of
 * RSA the signing algorithm could be specified as, for example,
 * "SHA256withRSA". The algorithm name must be
 * specified, as there is no default.
 *
 * <p> The name of the Cryptography Package Provider is designated
 * also by the Signature parameter to the constructor and the
 * {@code verify} method. If the provider is not
 * specified, the default provider is used. Each installation can
 * be configured to use a particular provider as default.
 *
 * <p> Potential applications of SignedObject include:
 * <ul>
 * <li> It can be used
 * internally to any Java runtime as an unforgeable authorization
 * token -- one that can be passed around without the fear that the
 * token can be maliciously modified without being detected.
 * <li> It
 * can be used to sign and serialize data/object for storage outside
 * the Java runtime (e.g., storing critical access control data on
 * disk).
 * <li> Nested SignedObjects can be used to construct a logical
 * sequence of signatures, resembling a chain of authorization and
 * delegation.
 * </ul>
 *
 * @see Signature
 *
 * @author Li Gong
 * @since 1.2
 */

public final class SignedObject implements Serializable {

 private static final long serialVersionUID = 720502720485447167L;

 /*
 * The original content is "deep copied" in its serialized format
 * and stored in a byte array. The signature field is also in the
 * form of byte array.
 */

 private byte[] content;
 private byte[] signature;
 private String thealgorithm;

 /**
 * Constructs a SignedObject from any Serializable object.
 * The given object is signed with the given signing key, using the
 * designated signature engine.
 *
 * @param object the object to be signed.
 * @param signingKey the private key for signing.
 * @param signingEngine the signature signing engine.
 *
 * @exception IOException if an error occurs during serialization
 * @exception InvalidKeyException if the key is invalid.
 * @exception SignatureException if signing fails.
 */
 public SignedObject(Serializable object, PrivateKey signingKey,
 Signature signingEngine)
 throws IOException, InvalidKeyException, SignatureException {
 // creating a stream pipe-line, from a to b
 ByteArrayOutputStream b = new ByteArrayOutputStream();
 ObjectOutput a = new ObjectOutputStream(b);

 // write and flush the object content to byte array
 a.writeObject(object);
 a.flush();
 a.close();
 this.content = b.toByteArray();
 b.close();

 // now sign the encapsulated object
 this.sign(signingKey, signingEngine);
 }

 /**
 * Retrieves the encapsulated object.
 * The encapsulated object is de-serialized before it is returned.
 *
 * @return the encapsulated object.
 *
 * @exception IOException if an error occurs during de-serialization
 * @exception ClassNotFoundException if an error occurs during
 * de-serialization
 */
 public Object getObject()
 throws IOException, ClassNotFoundException
 {
 // creating a stream pipe-line, from b to a
 ByteArrayInputStream b = new ByteArrayInputStream(this.content);
 ObjectInput a = new ObjectInputStream(b);
 Object obj = a.readObject();
 b.close();
 a.close();
 return obj;
 }

 /**
 * Retrieves the signature on the signed object, in the form of a
 * byte array.
 *
 * @return the signature. Returns a new array each time this
 * method is called.
 */
 public byte[] getSignature() {
 return this.signature.clone();
 }

 /**
 * Retrieves the name of the signature algorithm.
 *
 * @return the signature algorithm name.
 */
 public String getAlgorithm() {
 return this.thealgorithm;
 }

 /**
 * Verifies that the signature in this SignedObject is the valid
 * signature for the object stored inside, with the given
 * verification key, using the designated verification engine.
 *
 * @param verificationKey the public key for verification.
 * @param verificationEngine the signature verification engine.
 *
 * @exception SignatureException if signature verification failed (an
 * exception prevented the signature verification engine from completing
 * normally).
 * @exception InvalidKeyException if the verification key is invalid.
 *
 * @return {@code true} if the signature
 * is valid, {@code false} otherwise
 */
 public boolean verify(PublicKey verificationKey,
 Signature verificationEngine)
 throws InvalidKeyException, SignatureException {
 verificationEngine.initVerify(verificationKey);
 verificationEngine.update(this.content.clone());
 return verificationEngine.verify(this.signature.clone());
 }

 /*
 * Signs the encapsulated object with the given signing key, using the
 * designated signature engine.
 *
 * @param signingKey the private key for signing.
 * @param signingEngine the signature signing engine.
 *
 * @exception InvalidKeyException if the key is invalid.
 * @exception SignatureException if signing fails.
 */
 private void sign(PrivateKey signingKey, Signature signingEngine)
 throws InvalidKeyException, SignatureException {
 // initialize the signing engine
 signingEngine.initSign(signingKey);
 signingEngine.update(this.content.clone());
 this.signature = signingEngine.sign().clone();
 this.thealgorithm = signingEngine.getAlgorithm();
 }

 /**
 * readObject is called to restore the state of the SignedObject from
 * a stream.
 */
 private void readObject(java.io.ObjectInputStream s)
 throws java.io.IOException, ClassNotFoundException {
 java.io.ObjectInputStream.GetField fields = s.readFields();
 content = ((byte[])fields.get("content", null)).clone();
 signature = ((byte[])fields.get("signature", null)).clone();
 thealgorithm = (String)fields.get("thealgorithm", null);
 }
}