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);
}