Key unwrapping fails

Question

I want to protect a RSA private key stored in localStorage by wrapping it with a key derived from the user's password.

However when unwrapping the key the error DOMException: An invalid or illegal string was specified is thrown.

This is a minimal snippet for reproducing the issue:

const base64ToArrayBuffer = (data) => {
 const binaryKey = atob(data);
 const keyBytes = new Uint8Array(binaryKey.length);
 for (let i = 0; i < binaryKey.length; i++) {
 keyBytes[i] = binaryKey.charCodeAt(i);
 }
 return keyBytes.buffer;
}
const bufferToBase64 = (data) => btoa(String.fromCharCode(... new Uint8Array(data)));
const fn = async () => {
// Generate RSA key pair
 const keyPair = await crypto.subtle.generateKey({
 name: "RSA-OAEP",
 modulusLength: 4096,
 publicExponent: new Uint8Array([1, 0, 1]),
 hash: "SHA-512"
 }, true, ["encrypt", "decrypt"]);
// Save private key
// Encrypt the private key
 const textEncoder = new TextEncoder();
 const salt = new Uint8Array(16);
 crypto.getRandomValues(salt);
 const passwordKey = await crypto.subtle.importKey("raw", textEncoder.encode(window.prompt("password")), "PBKDF2", true, ["deriveKey"]);
 const derivedKey = await crypto.subtle.deriveKey({
 name: "PBKDF2",
 hash: "SHA-256",
 salt,
 iterations: 210000
 }, passwordKey, {
 name: "AES-CBC",
 length: 256
 }, true, ["wrapKey", "unwrapKey"]);
 const iv = new Uint8Array(16);
 crypto.getRandomValues(iv);
 const wrappedPrivateKey = await crypto.subtle.wrapKey("pkcs8", keyPair.privateKey, derivedKey, {
 name: "AES-CBC",
 iv
 });
 const b64WrappedPrivateKey = bufferToBase64(wrappedPrivateKey);
 const b64Salt = bufferToBase64(salt);
 const b64IV = bufferToBase64(iv);
 const encryptedPrivateKey = base64ToArrayBuffer(b64WrappedPrivateKey);
 const unwrapSalt = base64ToArrayBuffer(b64Salt);
 const unwrapIV = base64ToArrayBuffer(b64IV);
 const unwrapPasswordKey = await crypto.subtle.importKey("raw", textEncoder.encode(window.prompt("password unwrap")), "PBKDF2", true, ["deriveKey"]);
 const unwrappingKey = await crypto.subtle.deriveKey({
 name: "PBKDF2",
 hash: "SHA-256",
 salt: unwrapSalt,
 iterations: 210000
 }, unwrapPasswordKey, {
 name: "AES-CBC",
 length: 256
 }, true, ["wrapKey", "unwrapKey"]);
 try {
 const privateKey = await crypto.subtle.unwrapKey("pkcs8", encryptedPrivateKey, unwrappingKey, {
 name: "AES-CBC",
 iv: unwrapIV
 }, {
 name: "RSA-OAEP",
 hash: "SHA-512"
 }, true, ["encrypt", "decrypt"]);
 console.log("Success");
 } catch (err) {
 console.log(err);
 }
};
(async () => {
 await fn();
})()

Security is considered up to a certain point because this is just a demo project.

• user16540390: Can you create and provide a minimal reproducible example?
• iKingNinja: It's the code i posted
• user16540390: The posted code isn't minimal. Can you create a script without login, reload and storage that I can copy and paste to locally reproduce and debug the problem? It's also not complete. What is resData.id? Can you post the code as Stack Snippet?
• iKingNinja: I think this should do and resData.id is just the user's ID.
• user16540390: Which call causes the error?

Answer 1

After debugging with the Node.js crypto library, I found out that the actual error was Unsupported key usage for an RSA-OAEP key because I was passing the encrypt usage for a RSA private key which is not possible.