Add unit tests for PGP service (FRE-4692)

- 27 new tests covering all PGP service methods
- Fixes: armored public key in NewPGPService/GenerateKeyPair/EncryptBody,
  IsLocked check in getUnlockedKeyRing, aes256 cipher token in EncryptAttachment

Co-Authored-By: Paperclip <noreply@paperclip.ing>

internal/mail/pgp.go

@@ -25,15 +25,25 @@ func NewPGPService(privateKeyArmored string) (*PGPService, error) {
 		return nil, fmt.Errorf("failed to parse private key: %w", err)
 	}
 
-	publicKey, err := privateKey.GetPublicKey()
+	pubKeyBytes, err := privateKey.GetPublicKey()
 	if err != nil {
 		return nil, fmt.Errorf("failed to extract public key: %w", err)
 	}
 
+	pubKey, err := crypto.NewKey(pubKeyBytes)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse public key: %w", err)
+	}
+
+	pubArmor, err := pubKey.Armor()
+	if err != nil {
+		return nil, fmt.Errorf("failed to armor public key: %w", err)
+	}
+
 	return &PGPService{
 		keyRing: &PGPKeyRing{
 			PrivateKey:     privateKey,
-			PublicKey:      publicKey,
+			PublicKey:      []byte(pubArmor),
 			PrivateKeyData: []byte(privateKeyArmored),
 		},
 	}, nil
@@ -68,7 +78,7 @@ func (s *PGPService) EncryptBody(plaintext string, passphrase string) (string, e
 		return "", fmt.Errorf("failed to get public key: %w", err)
 	}
 
-	pubKey, err := crypto.NewKeyFromArmored(string(pubKeyBytes))
+	pubKey, err := crypto.NewKey(pubKeyBytes)
 	if err != nil {
 		return "", fmt.Errorf("failed to parse public key: %w", err)
 	}
@@ -131,11 +141,17 @@ func (s *PGPService) getUnlockedKeyRing(passphrase string) (*crypto.KeyRing, err
 	}
 
 	if passphrase != "" {
-		unlockedKey, err := key.Unlock([]byte(passphrase))
+		isLocked, err := key.IsLocked()
 		if err != nil {
-			return nil, fmt.Errorf("failed to unlock private key: %w", err)
+			return nil, fmt.Errorf("failed to check key lock status: %w", err)
+		}
+		if isLocked {
+			unlockedKey, err := key.Unlock([]byte(passphrase))
+			if err != nil {
+				return nil, fmt.Errorf("failed to unlock private key: %w", err)
+			}
+			key = unlockedKey
 		}
-		key = unlockedKey
 	}
 
 	return crypto.NewKeyRing(key)
@@ -176,7 +192,15 @@ func (s *PGPService) GenerateKeyPair(email string, passphrase string) (privateKe
 		return "", "", fmt.Errorf("failed to extract public key: %w", err)
 	}
 
-	pubArmor := string(pubKeyBytes)
+	pubKey, err := crypto.NewKey(pubKeyBytes)
+	if err != nil {
+		return "", "", fmt.Errorf("failed to parse public key: %w", err)
+	}
+
+	pubArmor, err := pubKey.Armor()
+	if err != nil {
+		return "", "", fmt.Errorf("failed to armor public key: %w", err)
+	}
 
 	return privateArmor, pubArmor, nil
 }
@@ -229,7 +253,7 @@ func (s *PGPService) EncryptAttachment(data []byte, recipientPublicKey *crypto.K
 
 	pgpMessage := crypto.NewPlainMessage(data)
 
-	sk, err := crypto.NewSessionKeyFromToken(symKey, "AES256").Encrypt(pgpMessage)
+	sk, err := crypto.NewSessionKeyFromToken(symKey, "aes256").Encrypt(pgpMessage)
 	if err != nil {
 		return nil, fmt.Errorf("failed to encrypt attachment: %w", err)
 	}
@@ -241,7 +265,7 @@ func (s *PGPService) EncryptAttachment(data []byte, recipientPublicKey *crypto.K
 	}
 
 	encryptedSymKey, err := recipientKeyRing.EncryptSessionKey(
-		crypto.NewSessionKeyFromToken(symKey, "AES256"),
+		crypto.NewSessionKeyFromToken(symKey, "aes256"),
 	)
 	if err != nil {
 		return nil, fmt.Errorf("failed to encrypt symmetric key: %w", err)