public bool Decrypt(EncryptedMessage encryptedMessage, int senderId, out string messageText) { if (encryptedMessage == null) { throw new ArgumentException("Encrypted message cannot be null"); } if (encryptedMessage.Body == null || encryptedMessage.DigitalSignature == null || encryptedMessage.SymmetricKey == null || encryptedMessage.Iv == null) { throw new ArgumentException("Not all encrypted message fields are initialized"); } IContactModel senderContact = _storageService.GetContacts().FirstOrDefault(c => c.Id == senderId); if (senderContact == null) { throw new ArgumentException("Contact with id of senderId does not exist"); } string receiverKeyPair = _storageService.GetUser().KeyPair; string senderPublicKey = senderContact.PublicKey; try { // decrypt symmetric key with receivers private key RsaCipher rsa = new RsaCipher(receiverKeyPair); byte[] encryptedSymmetricKeyBytes = FormatConverter.String64ToBytes(encryptedMessage.SymmetricKey); byte[] decryptedSymmetricKeyBytes = rsa.Decrypt(encryptedSymmetricKeyBytes); // decrypt message text with jsut decrypted symmetric key byte[] ivBytes = FormatConverter.String64ToBytes(encryptedMessage.Iv); AesCipher aes = new AesCipher(decryptedSymmetricKeyBytes, ivBytes); byte[] encryptedMessageBytes = FormatConverter.String64ToBytes(encryptedMessage.Body); byte[] decryptedMessageBytes = aes.Decrypt(encryptedMessageBytes); // set message text out parameter messageText = FormatConverter.BytesToString(decryptedMessageBytes); // verify digital signature rsa = new RsaCipher(senderPublicKey); byte[] digitalSignatureBytes = FormatConverter.String64ToBytes(encryptedMessage.DigitalSignature); bool signatureOk = rsa.VerifyDigitalSignature(decryptedMessageBytes, digitalSignatureBytes); return signatureOk; } catch (Exception ex) { messageText = null; return false; } }
public EncryptedMessage Encrypt(string messageText, int recieverId) { if (messageText == null) { throw new ArgumentException("Message text cannot be null"); } IContactModel receiverContact = _storageService.GetContacts().FirstOrDefault(c => c.Id == recieverId); if (receiverContact == null) { throw new ArgumentException("Contact with id of receiverId does not exist"); } EncryptedMessage encMsg = new EncryptedMessage(); AesCipher aes = new AesCipher(); // set initiazlization vector encMsg.Iv = FormatConverter.BytesToString64(aes.IV); // enccrypt message text symmetrically byte[] messageBytes = FormatConverter.StringToBytes(messageText); byte[] encryptedMessageBytes = aes.Encrypt(messageBytes); encMsg.Body = FormatConverter.BytesToString64(encryptedMessageBytes); // encrypt symmetric key with receivers public key string receiverPublicKey = receiverContact.PublicKey; RsaCipher rsa = new RsaCipher(receiverPublicKey); byte[] encryptedSymmetricKeyBytes = rsa.Encrypt(aes.Key); encMsg.SymmetricKey = FormatConverter.BytesToString64(encryptedSymmetricKeyBytes); // create digital signature of message text (using senders private key) string senderKeyPair = _storageService.GetUser().KeyPair; rsa = new RsaCipher(senderKeyPair); byte[] digitalSignatureBytes = rsa.CreateDigitalSignature(messageBytes); encMsg.DigitalSignature = FormatConverter.BytesToString64(digitalSignatureBytes); return encMsg; }