Encrypt session key to multiple keys in keyring. (#59)

`EncryptSessionKey` now creates encrypted key packet for each valid key
in keyring.

Co-authored-by: Aron Wussler <aron@wussler.it>

.golangci.yml

@@ -26,3 +26,4 @@ linters:
     - lll               # Reports long lines [fast: true, auto-fix: false]
     - testpackage       # Makes you use a separate _test package [fast: true, auto-fix: false]
     - wsl               # Whitespace Linter - Forces you to use empty lines! [fast: true, auto-fix: false]
+    - gofumpt           # Enforce a stricter format than gofmt

CHANGELOG.md

@@ -28,6 +28,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 - Improved key and message armoring testing
+- `EncryptSessionKey` now creates encrypted key packets for each valid encryption key in the provided keyring. 
+    Returns a byte slice with all the concatenated key packets.
 
 ### Fixed
 - Public key armoring headers

README.md

@@ -331,13 +331,13 @@ A session key can be generated, encrypted to a Asymmetric/Symmetric key packet a
 
 sessionKey, err := crypto.GenerateSessionKey()
 
-keyPacket, err := publicKeyRing.EncryptSessionKey(sessionKey)
+keyPacket, err := publicKeyRing.EncryptSessionKey(sessionKey) // Will encrypt to all the keys in the keyring
 keyPacketSymm, err := crypto.EncryptSessionKeyWithPassword(sessionKey, password)
 ```
 `KeyPacket` is a `[]byte` containing the session key encrypted with the private key or password.
 
 ```go
-decodedKeyPacket, err := privateKeyRing.DecryptSessionKey(keyPacket)
+decodedKeyPacket, err := privateKeyRing.DecryptSessionKey(keyPacket) // Will decode with the first valid key found
 decodedSymmKeyPacket, err := crypto.DecryptSessionKeyWithPassword(keyPacketSymm, password)
 ```
 `decodedKeyPacket` and `decodedSymmKeyPacket` are objects of type `*SymmetricKey` that can

crypto/keyring_session.go

@@ -48,26 +48,26 @@ func (keyRing *KeyRing) DecryptSessionKey(keyPacket []byte) (*SessionKey, error)
 // publicKey and returns a binary public-key encrypted session key packet.
 func (keyRing *KeyRing) EncryptSessionKey(sk *SessionKey) ([]byte, error) {
 	outbuf := &bytes.Buffer{}
-
 	cf, err := sk.GetCipherFunc()
 	if err != nil {
 		return nil, errors.Wrap(err, "gopenpgp: unable to encrypt session key")
 	}
 
-	var pub *packet.PublicKey
+	var pubKeys []*packet.PublicKey
 	for _, e := range keyRing.entities {
 		if encryptionKey, ok := e.EncryptionKey(getNow()); ok {
-			pub = encryptionKey.PublicKey
+			pubKeys = append(pubKeys, encryptionKey.PublicKey)
-			break
 		}
 	}
-	if pub == nil {
+	if len(pubKeys) == 0 {
 		return nil, errors.New("cannot set key: no public key available")
 	}
 
+	for _, pub := range pubKeys {
 		if err := packet.SerializeEncryptedKey(outbuf, pub, cf, sk.Key, nil); err != nil {
 			err = fmt.Errorf("gopenpgp: cannot set key: %v", err)
 			return nil, err
 		}
+	}
 	return outbuf.Bytes(), nil
 }

crypto/sessionkey_test.go

@@ -44,6 +44,21 @@ func TestAsymmetricKeyPacket(t *testing.T) {
 	assert.Exactly(t, testSessionKey, outputSymmetricKey)
 }
 
+func TestMultipleAsymmetricKeyPacket(t *testing.T) {
+	keyPacket, err := keyRingTestMultiple.EncryptSessionKey(testSessionKey)
+	if err != nil {
+		t.Fatal("Expected no error while generating key packet, got:", err)
+	}
+
+	// Password defined in keyring_test
+	outputSymmetricKey, err := keyRingTestMultiple.DecryptSessionKey(keyPacket)
+	if err != nil {
+		t.Fatal("Expected no error while decrypting key packet, got:", err)
+	}
+
+	assert.Exactly(t, testSessionKey, outputSymmetricKey)
+}
+
 func TestSymmetricKeyPacket(t *testing.T) {
 	password := []byte("I like encryption")
 
@@ -90,7 +105,8 @@ func TestDataPacketEncryption(t *testing.T) {
 	assert.Exactly(t, message.GetString(), decrypted.GetString())
 
 	// Encrypt session key
-	keyPacket, err := keyRingTestPublic.EncryptSessionKey(testSessionKey)
+	assert.Exactly(t, 3, len(keyRingTestMultiple.entities))
+	keyPacket, err := keyRingTestMultiple.EncryptSessionKey(testSessionKey)
 	if err != nil {
 		t.Fatal("Unable to encrypt key packet, got:", err)
 	}
@@ -108,6 +124,9 @@ func TestDataPacketEncryption(t *testing.T) {
 	if err != nil {
 		t.Fatal("Unable to unarmor pgp message, got:", err)
 	}
+	ids, ok := pgpMessage.getEncryptionKeyIDs()
+	assert.True(t, ok)
+	assert.Exactly(t, 3, len(ids))
 
 	// Test if final decryption succeeds
 	finalMessage, err := keyRingTestPrivate.Decrypt(pgpMessage, nil, 0)