subkey

npm install subkey

Create signatures based on an RSA key, but using a ed25519 session key to avoid signature oracle issues. Uses elliptic for ECDSA.

API

var subkey = require('subkey');
 
var signature = subkey.sign(yourPrivateKey, 'your message');
 
subkey.verify(yourPublicKey, signature, 'not your message');
// returns true
 
subkey.verify(yourPublicKey, signature, 'not your message');
// returns false

The first time you sign with an RSA key an ed25519 key is created and signed with your RSA key. This key is used to sign all messaged and they public key, and the key signature are included with the message signature each time you sign something. This ephemeral subkey is only saved in memory and will not be saved.

When verifying, the first time a key, session key, and session key signature combination is seen it is verified and will fail to verify if the session key in the signature does not match the RSA key. It then verifies against session key returning true or false depending on whether it verifies.

ASYNC!!!!

There are async methods, mainly in here for compatibility with ssh-agent, the api is

subkey.signAsync(yourPrivateKey, 'your message', signFunction, callback);
function signFunction (key, message, callback) {
   //obtain signature of message with key
   callback(null, sig);
}
subkey.verifyAsync(yourPublicKey, signature, 'your message', function (err, valid) {
  // err = null and valid = true
});
subkey.verifyAsync(yourPublicKey, signature, 'not your message', function (err, valid) {
  // err = null and valid = false
});
 

The sign function takes a key and a message and the callback must be called with the rsa-ssh1 signature of the message. This is used to sign the ephemeral key the rest of signing works the same.

verifyAsync is like verify except (beside being async) it uses sha1 as the hash method used to sign they subkey instead of sha-224 like the sync method. In other words they are not compatible.