v1.2.11: convert ECDSA ASN.1 signature to ECDSA JWT type

keypairs.js

@@ -229,13 +229,21 @@ Keypairs.signJws = function (opts) {
       }
 
       // node specifies RSA-SHAxxx even whet it's actually ecdsa (it's all encoded x509 shasums anyway)
-      var nodeAlg = "RSA-SHA" + (((protect||header).alg||'').replace(/^[^\d]+/, '')||'256');
+      var nodeAlg = "SHA" + (((protect||header).alg||'').replace(/^[^\d]+/, '')||'256');
       var protected64 = Enc.strToUrlBase64(protectedHeader);
       var payload64 = Enc.bufToUrlBase64(payload);
-      var sig = require('crypto')
+      var binsig = require('crypto')
         .createSign(nodeAlg)
         .update(protect ? (protected64 + "." + payload64) : payload64)
-        .sign(pem, 'base64')
+        .sign(pem)
+      ;
+      if (!opts.jwk || 'RSA' !== opts.jwk.kty) {
+        // ECDSA JWT signatures differ from "normal" ECDSA signatures
+        // https://tools.ietf.org/html/rfc7518#section-3.4
+        binsig = convertIfEcdsa(binsig);
+      }
+
+      var sig = binsig.toString('base64')
         .replace(/\+/g, '-')
         .replace(/\//g, '_')
         .replace(/=/g, '')
@@ -249,6 +257,35 @@ Keypairs.signJws = function (opts) {
       };
     }
 
+    function convertIfEcdsa(binsig) {
+      // should have asn1 sequence header of 0x30
+      if (0x30 !== binsig[0]) { return binsig; }
+      var index = 2; // first ecdsa "R" header byte
+      var len = binsig[1];
+      var lenlen = 0;
+      // Seek length of length if length is greater than 127 (i.e. two 512-bit / 64-byte R and S values)
+      if (0x80 & len) {
+        lenlen = len - 0x80;
+        // the length of the signature won't be over 256 bytes (2048 bits) for many years yet
+        if (1 !== lenlen) { return binsig; }
+        // the length is this number
+        len = binsig[2];
+        index += lenlen;
+      }
+      // should have bigint header of 0x02 followd by a single byte of length
+      if (0x02 !== binsig[index]) { return binsig; }
+      index += 1;
+      var rlen = binsig[index];
+      var r = binsig.slice(index + 1, index + 1 + rlen);
+      var slen = binsig[index + 1 + rlen + 1]; // skip header and read length
+      var s = binsig.slice(index + 1 + rlen + 1 + 1);
+      if (slen !== s.byteLength) { return binsig; }
+      // There may be one byte of padding on either
+      if (33 === r.byteLength) { r = r.slice(1); }
+      if (33 === s.byteLength) { s = s.slice(1); }
+      return Buffer.concat([r, s]);
+    }
+
     if (opts.pem && opts.jwk) {
       return sign(opts.pem);
     } else {

package.json

@@ -1,6 +1,6 @@
 {
   "name": "keypairs",
-  "version": "1.2.9",
+  "version": "1.2.11",
   "description": "Lightweight RSA/ECDSA keypair generation and JWK <-> PEM",
   "main": "keypairs.js",
   "files": [

test.js

@@ -1,6 +1,7 @@
 var Keypairs = require('./');
 
 /* global Promise*/
+console.info("This SHOULD result in an error message:");
 Keypairs.parseOrGenerate({ key: '' }).then(function (pair) {
   // should NOT have any warning output
   if (!pair.private || !pair.public) {