comb4p.cpp

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/*
* Comb4P hash combiner
* (C) 2010 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
 
#include <botan/comb4p.h>
#include <botan/internal/xor_buf.h>
#include <stdexcept>
 
namespace Botan {
 
namespace {
 
void comb4p_round(MemoryRegion<byte>& out,
                  const MemoryRegion<byte>& in,
                  byte round_no,
                  HashFunction* h1,
                  HashFunction* h2)
   {
   h1->update(round_no);
   h2->update(round_no);
 
   h1->update(&in[0], in.size());
   h2->update(&in[0], in.size());
 
   SecureVector<byte> h_buf = h1->final();
   xor_buf(&out[0], &h_buf[0], std::min(out.size(), h_buf.size()));
 
   h_buf = h2->final();
   xor_buf(&out[0], &h_buf[0], std::min(out.size(), h_buf.size()));
   }
 
}
 
Comb4P::Comb4P(HashFunction* h1, HashFunction* h2) :
   hash1(h1), hash2(h2)
   {
   if(hash1->name() == hash2->name())
      throw std::invalid_argument("Comb4P: Must use two distinct hashes");
 
   if(hash1->output_length() != hash2->output_length())
      throw std::invalid_argument("Comb4P: Incompatible hashes " +
                                  hash1->name() + " and " +
                                  hash2->name());
 
   clear();
   }
 
size_t Comb4P::hash_block_size() const
   {
   if(hash1->hash_block_size() == hash2->hash_block_size())
      return hash1->hash_block_size();
 
   /*
   * Return LCM of the block sizes? This would probably be OK for
   * HMAC, which is the main thing relying on knowing the block size.
   */
   return 0;
   }
 
void Comb4P::clear()
   {
   hash1->clear();
   hash2->clear();
 
   // Prep for processing next message, if any
   hash1->update(0);
   hash2->update(0);
   }
 
void Comb4P::add_data(const byte input[], size_t length)
   {
   hash1->update(input, length);
   hash2->update(input, length);
   }
 
void Comb4P::final_result(byte out[])
   {
   SecureVector<byte> h1 = hash1->final();
   SecureVector<byte> h2 = hash2->final();
 
   // First round
   xor_buf(&h1[0], &h2[0], std::min(h1.size(), h2.size()));
 
   // Second round
   comb4p_round(h2, h1, 1, hash1, hash2);
 
   // Third round
   comb4p_round(h1, h2, 2, hash1, hash2);
 
   copy_mem(out            , &h1[0], h1.size());
   copy_mem(out + h1.size(), &h2[0], h2.size());
 
   // Prep for processing next message, if any
   hash1->update(0);
   hash2->update(0);
   }
 
}