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/* -*-c++-*- */
#include "myccm.hh"
#include <bitset>

bool MyCCM::decrypt(const std::string &ciphertext, std::string &plaintext) {

  // Cropping the tag out of the plaintext
  std::string tag(ciphertext.end() - mac_tag_length, ciphertext.end());
  std::string cropped_cipher = ciphertext.substr(0, ciphertext.size() - mac_tag_length);
  BlockA A(l_length, nonce);
  ++A;
  
  //Decrypt text with XOR
  size_t pos = 0;
  while(pos < cropped_cipher.length())
  {
    BlockS keystream;
    encrypt_block(A, keystream);
    ++A;

    for(size_t i = 0; i < std::min(Block::size(), cropped_cipher.length() - pos); i++)
    {
      plaintext += cropped_cipher[pos + i] ^ keystream.data()[i];
    }
    
    pos += Block::size();
  }

  return true;
}

bool MyCCM::encrypt(const std::string &plaintext, std::string &ciphertext) {

  //Compute Xn
  BlockB B(mac_tag_length, l_length, nonce, plaintext);
  BlockX X;
  X.type(Block::Type::X);

  encrypt_block(B, X);
  while(++B)
  {
    xor_blocks(X, B, X);
    encrypt_block(X, X);
  }

  //Encrypt message
  BlockA A(l_length, nonce);
  ++A;
  ciphertext.clear();
  size_t pos = 0;
  while(pos < plaintext.length())
  {
    BlockS keystream;
    encrypt_block(A, keystream);
    ++A;
    
    for(size_t i = 0; i < std::min(Block::size(), plaintext.length() - pos); i++)
    {
      ciphertext += (plaintext[pos + i] ^ keystream.data()[i]);
    }
    pos += Block::size();
  }
  //Add MAC tag
  BlockS S;
  BlockA A_temp(l_length, nonce);
  encrypt_block(A_temp, S);
  BlockT T(mac_tag_length, S, X);
  ciphertext += T.tag();

  return true;
}