/*

* RFC 6979 Deterministic Nonce Generator

* (C) 2014,2015 Jack Lloyd

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#include <botan/internal/rfc6979.h>

#include <botan/hmac_drbg.h>

#include <botan/mac.h>

namespace Botan {

RFC6979_Nonce_Generator::RFC6979_Nonce_Generator(const std::string& hash,

                                                 const BigInt& order,

                                                 const BigInt& x) :

   m_order(order),

   m_qlen(m_order.bits()),

   m_rlen(m_qlen / 8 + (m_qlen % 8 ? 1 : 0)),

   m_rng_in(m_rlen * 2),

   m_rng_out(m_rlen)

   {

   m_hmac_drbg.reset(new HMAC_DRBG(MessageAuthenticationCode::create("HMAC(" + hash + ")")));

   BigInt::encode_1363(m_rng_in.data(), m_rlen, x);

   }

RFC6979_Nonce_Generator::~RFC6979_Nonce_Generator()

   {

   // for ~unique_ptr

   }

const BigInt& RFC6979_Nonce_Generator::nonce_for(const BigInt& m)

   {

   BigInt::encode_1363(&m_rng_in[m_rlen], m_rlen, m);

   m_hmac_drbg->clear();

   m_hmac_drbg->initialize_with(m_rng_in.data(), m_rng_in.size());

   do

      {

      m_hmac_drbg->randomize(m_rng_out.data(), m_rng_out.size());

      m_k.binary_decode(m_rng_out.data(), m_rng_out.size());

      m_k >>= (8*m_rlen - m_qlen);

      }

   while(m_k == 0 || m_k >= m_order);

   return m_k;

   }

BigInt generate_rfc6979_nonce(const BigInt& x,

                              const BigInt& q,

                              const BigInt& h,

                              const std::string& hash)

   {

   RFC6979_Nonce_Generator gen(hash, q, x);

   BigInt k = gen.nonce_for(h);

   return k;

   }

}