Encode and decode the k value for hmac keys

Author: anakinj

CHANGELOG.md

@@ -12,6 +12,7 @@
 - Support only stricter base64 decoding (RFC 4648) [#658](https://github.com/jwt/ruby-jwt/pull/658) ([@anakinj](https://github.com/anakinj))
 - Custom algorithms are required to include `JWT::JWA::SigningAlgorithm` [#660](https://github.com/jwt/ruby-jwt/pull/660) ([@anakinj](https://github.com/anakinj))
 - Require RSA keys to be at least 2048 bits [#661](https://github.com/jwt/ruby-jwt/pull/661) ([@anakinj](https://github.com/anakinj))
+- Base64 encode and decode the k value for HMAC JWKs [#662](https://github.com/jwt/ruby-jwt/pull/662) ([@anakinj](https://github.com/anakinj))
 
 Take a look at the [upgrade guide](UPGRADING.md) for more details.
 

UPGRADING.md

@@ -39,4 +39,8 @@ Claim verification has been [split into separate classes](https://github.com/jwt
 
 The internal algorithms were [restructured](https://github.com/jwt/ruby-jwt/pull/607) to support extensions from separate libraries. The changes led to a few deprecations and new requirements:
 - The `sign` and `verify` static methods on all the algorithms (`::JWT::JWA`) will be removed.
-- Custom algorithms are expected to include the `JWT::JWA::SigningAlgorithm` module.
+- Custom algorithms are expected to include the `JWT::JWA::SigningAlgorithm` module.
+
+## Base64 the `k´ value for HMAC JWKs
+
+The gem was missing the Base64 encoding and decoding when representing and parsing a HMAC key as a JWK. This issue is now addressed. The added encoding will break compatibility with JWKs produced by older versions of the gem.

lib/jwt/jwk/hmac.rb

@@ -70,15 +70,15 @@ def []=(key, value)
       private
 
       def secret
-        self[:k]
+        @secret ||= ::JWT::Base64.url_decode(self[:k])
       end
 
       def extract_key_params(key)
         case key
         when JWT::JWK::HMAC
           key.export(include_private: true)
         when String # Accept String key as input
-          { kty: KTY, k: key }
+          { kty: KTY, k: ::JWT::Base64.url_encode(key) }
         when Hash
           key.transform_keys(&:to_sym)
         else

spec/jwt/jwk/hmac_spec.rb

@@ -73,6 +73,15 @@
         end
       end
     end
+
+    context 'when example from RFC' do
+      let(:params) { { kty: 'oct', k: 'AyM1SysPpbyDfgZld3umj1qzKObwVMkoqQ-EstJQLr_T-1qS0gZH75aKtMN3Yj0iPS4hcgUuTwjAzZr1Z9CAow' } }
+
+      it 'decodes the k' do
+        expected_key = "\x03#5K+\x0F\xA5\xBC\x83~\x06ew{\xA6\x8FZ\xB3(\xE6\xF0T\xC9(\xA9\x0F\x84\xB2\xD2P.\xBF\xD3\xFBZ\x92\xD2\x06G\xEF\x96\x8A\xB4\xC3wb=\"=.!r\x05.O\b\xC0\xCD\x9A\xF5g\xD0\x80\xA3".dup.force_encoding('ASCII-8BIT')
+        expect(subject.verify_key).to eq(expected_key)
+      end
+    end
   end
 
   describe '#[]=' do

spec/jwt/jwk/set_spec.rb

@@ -13,14 +13,14 @@
       end
 
       it 'from a JWKS hash with symbol keys' do
-        jwks = { keys: [{ kty: 'oct', k: 'testkey' }] }
-        jwk = JWT::JWK.new({ kty: 'oct', k: 'testkey' })
+        jwks = { keys: [{ kty: 'oct', k: Base64.strict_encode64('testkey') }] }
+        jwk = JWT::JWK.new({ kty: 'oct', k: Base64.strict_encode64('testkey') })
         expect(described_class.new(jwks).keys).to eql([jwk])
       end
 
       it 'from a JWKS hash with string keys' do
-        jwks = { 'keys' => [{ 'kty' => 'oct', 'k' => 'testkey' }] }
-        jwk = JWT::JWK.new({ kty: 'oct', k: 'testkey' })
+        jwks = { 'keys' => [{ 'kty' => 'oct', 'k' => Base64.strict_encode64('testkey') }] }
+        jwk = JWT::JWK.new({ kty: 'oct', k: Base64.strict_encode64('testkey') })
         expect(described_class.new(jwks).keys).to eql([jwk])
       end
 
@@ -30,7 +30,7 @@
       end
 
       it 'from an existing JWT::JWK::Set' do
-        jwk = JWT::JWK.new({ kty: 'oct', k: 'testkey' })
+        jwk = JWT::JWK.new({ kty: 'oct', k: Base64.strict_encode64('testkey') })
         jwks = described_class.new(jwk)
         expect(described_class.new(jwks)).to eql(jwks)
       end
@@ -43,7 +43,7 @@
 
   describe '.export' do
     it 'exports the JWKS to Hash' do
-      jwk = JWT::JWK.new({ kty: 'oct', k: 'testkey' })
+      jwk = JWT::JWK.new({ kty: 'oct', k: Base64.strict_encode64('testkey') })
       jwks = described_class.new(jwk)
       exported = jwks.export
       expect(exported[:keys].size).to eql(1)
@@ -53,15 +53,15 @@
 
   describe '.eql?' do
     it 'correctly classifies equal sets' do
-      jwk = JWT::JWK.new({ kty: 'oct', k: 'testkey' })
+      jwk = JWT::JWK.new({ kty: 'oct', k: Base64.strict_encode64('testkey') })
       jwks1 = described_class.new(jwk)
       jwks2 = described_class.new(jwk)
       expect(jwks1).to eql(jwks2)
     end
 
     it 'correctly classifies different sets' do
-      jwk1 = JWT::JWK.new({ kty: 'oct', k: 'testkey' })
-      jwk2 = JWT::JWK.new({ kty: 'oct', k: 'testkex' })
+      jwk1 = JWT::JWK.new({ kty: 'oct', k: Base64.strict_encode64('testkey') })
+      jwk2 = JWT::JWK.new({ kty: 'oct', k: Base64.strict_encode64('testkex') })
       jwks1 = described_class.new(jwk1)
       jwks2 = described_class.new(jwk2)
       expect(jwks1).not_to eql(jwks2)
@@ -72,8 +72,8 @@
   #       but Array#uniq! doesn't recognize this, despite the documentation saying otherwise
   describe '.uniq!' do
     it 'filters out equal keys' do
-      jwk = JWT::JWK.new({ kty: 'oct', k: 'testkey' })
-      jwk2 = JWT::JWK.new({ kty: 'oct', k: 'testkey' })
+      jwk = JWT::JWK.new({ kty: 'oct', k: Base64.strict_encode64('testkey') })
+      jwk2 = JWT::JWK.new({ kty: 'oct', k: Base64.strict_encode64('testkey') })
       jwks = described_class.new([jwk, jwk2])
       jwks.uniq!
       expect(jwks.keys.size).to eql(1)