ECDSA signatures between Node.js and WebCrypto appear to be incompatible?

Question

I'm using the following example for signing + verifying in Node.js: https://github.com/nodejs/node-v0.x-archive/issues/6904. The verification succeeds in Node.js but fails in WebCrypto. Similarly, a message signed using WebCrypto fails to verify in Node.js.

Here's the code I used to verify a signature produced from the Node.js script using WebCrypto - https://jsfiddle.net/aj49e8sj/. Tested in both Chrome 54.0.2840.27 and Firefox 48.0.2

// From https://github.com/nodejs/node-v0.x-archive/issues/6904
var keys = {
  priv: '-----BEGIN EC PRIVATE KEY-----\n' +
        'MHcCAQEEIF+jnWY1D5kbVYDNvxxo/Y+ku2uJPDwS0r/VuPZQrjjVoAoGCCqGSM49\n' +
        'AwEHoUQDQgAEurOxfSxmqIRYzJVagdZfMMSjRNNhB8i3mXyIMq704m2m52FdfKZ2\n' +
        'pQhByd5eyj3lgZ7m7jbchtdgyOF8Io/1ng==\n' +
        '-----END EC PRIVATE KEY-----\n',
  pub: '-----BEGIN PUBLIC KEY-----\n' +
       'MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEurOxfSxmqIRYzJVagdZfMMSjRNNh\n' +
       'B8i3mXyIMq704m2m52FdfKZ2pQhByd5eyj3lgZ7m7jbchtdgyOF8Io/1ng==\n' +
       '-----END PUBLIC KEY-----\n'
};
var message = (new TextEncoder('UTF-8')).encode('hello');

// Algorithm used in Node.js script is ecdsa-with-SHA1, key generated with prime256v1
var algorithm = {
    name: 'ECDSA',
    namedCurve: 'P-256',
    hash: {
        name: 'SHA-1'
    }
};

// Signature from obtained via above Node.js script
var sig64 = 'MEUCIQDkAtiomagyHFi7dNfxMrzx/U0Gk/ZhmwCqaL3TimvlswIgPgeDqgZNqfR5/FZZASYsczUAhGSXjuycLhWnvk20qKc=';

// Decode base64 string into ArrayBuffer
var b64Decode = (str) => Uint8Array.from(atob(str), x => x.charCodeAt(0));

// Get base64 string from public key
const key64 = keys.pub.split('\n')
    .filter(x => x.length > 0 && !x.startsWith('-----'))
    .join('');

// Convert to buffers
var sig = b64Decode(sig64);
var keySpki = b64Decode(key64);

// Import and verify
// Want 'Verification result: true' but will get 'false'
var importKey = crypto.subtle.importKey('spki', keySpki, algorithm, true, ['verify'])
    .then(key => crypto.subtle.verify(algorithm, key, sig, message))
    .then(result => console.log('Verification result: ' + result));

Related question with a similar issue using SHA-256 instead of SHA-1: Generating ECDSA signature with Node.js/crypto

Things I've checked:

• I decoded the Node.js keys and verified they have the same OID as keys generated via WebCrypto. This tells me I'm using the correct curves.
• SHA-1 is explicitly identified as the hash to use in both locations.
• ECDSA is explicitly identified in both Node.js and WebCrypto.

How can I successfully verify the signature received from Node.js and vice versa - verify a signature in Node.js produced from WebCrypto? Or are the implementations of the standard subtly different in such a way that makes them incompatible?

Edit:

• WebCrypto signature (64 bytes): uTaUWTfF+AjN3aPj0b5Z2d1HybUEpV/phv/P9RtfKaGXtcYnbgfO43IRg46rznG3/WnWwJ2sV6mPOEnEPR0vWw==
• Node.js signature (71 bytes): MEUCIQDkAtiomagyHFi7dNfxMrzx/U0Gk/ZhmwCqaL3TimvlswIgPgeDqgZNqfR5/FZZASYsczUAhGSXjuycLhWnvk20qKc=

Verified Node.js signature is DER encoded and WebCrypto signature is not.

Answer 1

Having not used either of these libraries I can't say for certain, but one possibility is that they don't use the same encoding type for the signature. For DSA/ECDSA there are two main formats, IEEE P1363 (used by Windows) and DER (used by OpenSSL).

The "Windows" format is to have a preset size (determined by Q for DSA and P for ECDSA (Windows doesn't support Char-2, but if it did it'd probably be M for Char-2 ECDSA)). Then both r and s are left-padded with 0 until they meet that length.

In the too small to be legal example of r = 0x305 and s = 0x810522 with sizeof(Q) being 3 bytes:

// r
000305
// s
810522

For the "OpenSSL" format it is encoded under the rules of DER as SEQUENCE(INTEGER(r), INTEGER(s)), which looks like

// SEQUENCE
30
  // (length of payload)
  0A
  // INTEGER(r)
  02
    // (length of payload)
    02
    // note the leading 0x00 is omitted
    0305
  // INTEGER(s)
  02
    // (length of payload)
    04
    // Since INTEGER is a signed type, but this represented a positive number,
    // a 0x00 has to be inserted to keep the sign bit clear.
    00810522

or, compactly:

• Windows: 000305810522
• OpenSSL: 300A02020305020400810522

The "Windows" format is always even, always the same length. The "OpenSSL" format is usually about 6 bytes bigger, but can gain or lose a byte in the middle; so it's sometimes even, sometimes odd.

Base64-decoding your sig64 value shows that it is using the DER encoding. Generate a couple signatures with WebCrypto; if any don't start with 0x30 then you have the IEEE/DER problem.

Answer 2

After many hours finally find a solution with zero dependences!!

In browser:

      // Tip: Copy & Paste in the console for test.

      // Text to sign:
      var source = 'test';

      // Auxs
      function length(hex) {
        return ('00' + (hex.length / 2).toString(16)).slice(-2).toString();
      }

      function pubKeyToPEM(key) {
        var pem = '-----BEGIN PUBLIC KEY-----\n',
            keydata = '',
            bytes = new Uint8Array( key );

        for (var i = 0; i < bytes.byteLength; i++) {
          keydata += String.fromCharCode( bytes[ i ] );
        }

        keydata = window.btoa(keydata);

        while(keydata.length > 0) {
          pem += keydata.substring(0, 64) + '\n';
          keydata = keydata.substring(64);
        }

        pem = pem + "-----END PUBLIC KEY-----";

        return pem;
      }

      // Generate new keypair.
      window.crypto.subtle.generateKey({ name: "ECDSA", namedCurve: "P-384" }, true, ["sign", "verify"])
            .then(function(keypair) {

              // Encode as UTF-8
              var enc = new TextEncoder('UTF-8'),
                  digest = enc.encode(source);
              
              // Sign with subtle
              window.crypto.subtle.sign({ name: "ECDSA", hash: {name: "SHA-1"} }, keypair.privateKey, digest)
                    .then(function(signature) {
                        signature = new Uint8Array(signature);

                        // Extract r & s and format it in ASN1 format.
                        var signHex = Array.prototype.map.call(signature, function(x) { return ('00' + x.toString(16)).slice(-2); }).join(''),
                            r = signHex.substring(0, 96),
                            s = signHex.substring(96),
                            rPre = true,
                            sPre = true;

                        while(r.indexOf('00') === 0) {
                          r = r.substring(2);
                          rPre = false;
                        }

                        if (rPre && parseInt(r.substring(0, 2), 16) > 127) {
                          r = '00' + r;
                        }

                        while(s.indexOf('00') === 0) {
                          s = s.substring(2);
                          sPre = false;
                        }

                        if(sPre && parseInt(s.substring(0, 2), 16) > 127) {
                          s = '00' + s;
                        }

                        var payload = '02' + length(r) + r +
                                      '02' + length(s) + s,
                            der = '30' + length(payload) + payload;
                        
                        // Export public key un PEM format (needed by node)
                        window.crypto.subtle.exportKey('spki', keypair.publicKey)
                                                   .then(function(key) {
                                                      var pubKey = pubKeyToPEM(key);
                                                      
                                                      console.log('This is pubKey -> ', pubKey);
                                                      console.log('This is signature -> ', der);                                                      
                                                   });
                                         
                        
                        // For test, we verify the signature, nothing, anecdotal.
                        window.crypto.subtle.verify({ name: "ECDSA", hash: {name: "SHA-1"} }, keypair.publicKey, signature, digest)
                              .then(console.log);
                    });
                    
            });

In node:

const crypto = require('crypto');

// ----------------------------------------------------------------------------

// Paste from browser!

var puKeyPem = '-----BEGIN PUBLIC KEY-----\n' +
               'MHYwEAYHKoZIzj0CAQYFK4EEACIDYgAEmDubwJuORpMMoMnvv59W8tU8PxPChh75\n' +
               'vjlfVB2+tPY5KDy1I0ohz2US+2K1T/ROcDCSRAjyONRzzwVBm9S6bqbk3KuaT2KG\n' +
               'ikoe0KLfTeQtdEUyq8J0aEOKRXoCJLZq\n' +
               '-----END PUBLIC KEY-----';
               
var hexSign = '306402305df22aa5f4e7200b7c264c891cd3a8c5b4622c25872020832d5bb3d251773592020249a46a8349754dc58c47c4cbb7c9023053b929a98f5c8cccf2c1a4746d82fc751e044b1f76dffdf9ef73f73bee1499c5e20aadddda41e3373760b8b0f3c1bbb2';

// ----------------------------------------------------------------------------

var verifier = crypto.createVerify('sha1'),
    digest   = 'test';
    
verifier.update(digest);
verifier.end();

console.log(verifier.verify(puKeyPem, hexSign, 'hex'));

// ----------------------------------------------------------------------------