Implement HS256 verify

index.js

@@ -2,30 +2,61 @@ const util = require('util');
 const base64url = require('base64url');
 const crypto = require('crypto');
 
-exports.sign = function _jwsSign() {
+exports.sign = function jwsSign() {
   const opts = {};
-  if (typeof arguments[0] === 'object') {
+  if (typeof arguments[0] === 'object')
     return jwsSign(arguments[0]);
-  }
   if (arguments.length === 2) {
     opts.header = { alg : 'HS256' };
     opts.payload = arguments[0];
     opts.secret = arguments[1];
-    return jwsSign(opts);
+    return jwsHS256Sign(opts);
   }
 }
 
-function jwsSign(opts) {
+function jwsHS256Sign(opts) {
   var payload = opts.payload;
   if (typeof opts.payload === 'object')
     payload = JSON.stringify(opts.payload);
+  const secret = opts.secret;
   const header = JSON.stringify(opts.header);
-  const hmac = crypto.createHmac('SHA256', opts.secret);
-  hmac.update(payload);
-  const signature = hmac.digest('base64');
+  const signature = createHS256Signature(header, payload, secret);
+  return jwsOutput(header, payload, signature);
+}
+
+function jwsOutput(header, payload, signature) {
   return util.format(
     '%s.%s.%s',
     base64url(header),
     base64url(payload),
-    base64url.fromBase64(signature));
+    signature);
+}
+
+function createHS256Signature(header, payload, secret) {
+  const hmac = crypto.createHmac('SHA256', secret);
+  const encodedHeader = base64url(header);
+  const encodedPayload = base64url(payload);
+  hmac.update(encodedHeader);
+  hmac.update('.');
+  hmac.update(encodedPayload);
+  const signature = hmac.digest('base64');
+  return base64url.fromBase64(signature);
+}
+
+exports.verify = function jwsVerify(jwsObject, keyOrSecret) {
+  const parts = jwsObject.split('.');
+  const encodedHeader = parts[0];
+  const encodedPayload = parts[1];
+  const encodedSignature = parts[2];
+  const rawHeader = base64url.decode(encodedHeader);
+  const payload = base64url.decode(encodedPayload);
+  const header = JSON.parse(rawHeader);
+  if (header.alg === 'HS256')
+    return jwsHS256Verify(rawHeader, payload, keyOrSecret, encodedSignature)
+}
+
+function jwsHS256Verify(header, payload, secret, expectedSignature) {
+  const calculatedSignature =
+    createHS256Signature(header, payload, secret);
+  return expectedSignature === calculatedSignature;
 }

test/jws.test.js

@@ -3,7 +3,7 @@ const crypto = require('crypto');
 const test = require('tap').test;
 const jws = require('..');
 
-test('HS256 algorithm', function (t) {
+test('HS256 algorithm, signing', function (t) {
   const testString = 'oh hey';
   const secret = 'sup';
   const expectedHeader = { alg: 'HS256' };
@@ -12,16 +12,22 @@ test('HS256 algorithm', function (t) {
   const parts = jwsObject.split('.');
   const header = JSON.parse(base64url.decode(parts[0]));
   const payload = base64url.decode(parts[1]);
-  const signature = base64url.toBase64(parts[2]);
-
-  const hmac = crypto.createHmac('SHA256', secret);
-  hmac.update(testString);
-  const expectedSignature = hmac.digest('base64');
 
   t.same(payload, testString, 'payload should match test string');
   t.same(header, expectedHeader, 'header should match expectation');
-  t.same(signature, expectedSignature, 'signatures should match');
   t.end();
 });
 
+test('HS256 algorithm, verifying', function (t) {
+  const testString = 'oh hey';
+  const secret = 'sup';
+  const jwsObject = jws.sign(testString, secret);
+
+  const verified = jws.verify(jwsObject, secret);
+  t.ok(verified, 'should be verified');
+
+  const notVerified = jws.verify(jwsObject, 'some other thing');
+  t.notOk(notVerified, 'should not be verified');
+  t.end();
+});