/*
* SSLv3 PRF
* (C) 2004-2006 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/

#include <botan/prf_ssl3.h>
#include <botan/symkey.h>
#include <botan/exceptn.h>
#include <botan/sha160.h>
#include <botan/md5.h>
#include <memory>

namespace Botan {

namespace {

/*
* Return the next inner hash
*/
OctetString next_hash(u32bit where, u32bit want,
                      HashFunction& md5, HashFunction& sha1,
                      const byte secret[], u32bit secret_len,
                      const byte seed[], u32bit seed_len)
   {
   if(want > md5.OUTPUT_LENGTH)
      throw Internal_Error("SSL3_PRF:next_hash: want is too big");

   const byte ASCII_A_CHAR = 0x41;

   for(u32bit j = 0; j != where + 1; j++)
      sha1.update(ASCII_A_CHAR + where);
   sha1.update(secret, secret_len);
   sha1.update(seed, seed_len);
   SecureVector<byte> sha1_hash = sha1.final();

   md5.update(secret, secret_len);
   md5.update(sha1_hash);
   SecureVector<byte> md5_hash = md5.final();

   return OctetString(&md5_hash[0], want);
   }

}

/*
* SSL3 PRF
*/
SecureVector<byte> SSL3_PRF::derive(u32bit key_len,
                                    const byte secret[], u32bit secret_len,
                                    const byte seed[], u32bit seed_len) const
   {
   if(key_len > 416)
      throw Internal_Error("SSL3_PRF: Requested key length is too large");

   MD5 md5;
   SHA_160 sha1;

   OctetString output;

   int counter = 0;
   while(key_len)
      {
      const u32bit produce = std::min(key_len, md5.OUTPUT_LENGTH);

      output = output + next_hash(counter++, produce, md5, sha1,
                                  secret, secret_len, seed, seed_len);

      key_len -= produce;
      }

   return output.bits_of();
   }

}