Sending IVCiphertext over communication channel

[Ruth1993]

Hello!

I have a question about sending an IVCiphertext over a communication channel. So I used the communication layer as provided by libscapi. Now I want to send an IVCiphertext from one party to the other over this communication channel. However, I get a segmentation fault and I can't figure out what's the problem. My functions for sending and receiving are as follows:

Send function:

void send_aes_msg(shared_ptr<SymmetricCiphertext> c_m) {
    string c_m_string = c_m->toString();
    channel->writeWithSize(c_m_string);
}

Receive function:

shared_ptr<SymmetricCiphertext> recv_aes_msg() {
  shared_ptr<IVCiphertext> c_m;

  vector<byte> raw_msg;
    channel->readWithSizeIntoVector(raw_msg);
  c_m->initFromByteVector(raw_msg);

  return c_m;
}

I have implemented similar functions for ElGamal ciphertexts and ElGamal keys, and in those cases I used the libscapi function for generating sendable data and it works. However, there is no such function for symmetric ciphertexts, so that's why I tried it this way, but apparently it doesn't work.

Could anyone help me out? Thanks a lot!

Kind regards, Ruth

[liorko87]

Hello @Ruth1993,

As far as I understand, you are trying to send cipher text between two parties. Did you get any error messages or exceptions during the execution? How did you create the channels?

Lior

[Ruth1993]

Hi Lior,

Yes, I'm trying to send a ciphertext between two parties. When two parties send and receive messages using the above two functions, the receiving party gets a segmentation fault, which is due to the line c_m->initFromByteVector(raw_msg); in the receive function. I already assumed something must be wrong there, but I can't figure out the proper way of parsing an IVCiphertext obtained over a communication channel.

I created the channel for both parties as follows (for the second party p1 and p2 are switched in the declaration of the channel object of course):

boost::asio::io_service io_service;

SocketPartyData p1 = SocketPartyData(boost_ip::address::from_string("127.0.0.1"), 8000);
SocketPartyData p2 = SocketPartyData(boost_ip::address::from_string("127.0.0.1"), 8001);

channel = make_shared<CommPartyTCPSynced>(io_service, p1, p2);

boost::thread t(boost::bind(&boost::asio::io_service::run, &io_service));

etc

Kind regards, Ruth

[liorko87]

@Ruth1993 In the sender function, how did you init the SymmetricCiphertext?

[Ruth1993]

@liorko87 I have an AES object, initialized by make_shared<OpenSSLCTREncRandomIV>("AES"), which encrypts a ByteArrayPlaintext object using its default encrypt function, so I assume it returns an IVCiphertextobject.

[Ruth1993]

I managed to fix the issue. I found a bug in the function toString() in class IVCiphertext, for which I created a pull request. Also, I found a bug in my own code (c_m needs to initialized), so I defined the function for receiving AES messages as follows (sending functions stays the same):

shared_ptr<SymmetricCiphertext> recv_aes_msg() {
  vector<byte> empty;
  shared_ptr<SymmetricCiphertext> c_m = make_shared<IVCiphertext>(make_shared<ByteArraySymCiphertext>(empty), empty);

  vector<byte> raw_msg;
  channel->readWithSizeIntoVector(raw_msg);

  const byte* uc = &(raw_msg[0]);
  string msg = string(reinterpret_cast<char const*>(uc), raw_msg.size());
  c_m->initFromString(msg);

  return c_m;
}