/*

* 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>

#include <botan/internal/fmt.h>

namespace Botan {

RFC6979_Nonce_Generator::RFC6979_Nonce_Generator(std::string_view 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 = std::make_unique<HMAC_DRBG>(MessageAuthenticationCode::create_or_throw(fmt("HMAC({})", hash)));

   x.serialize_to(std::span{m_rng_in}.first(m_rlen));

}

RFC6979_Nonce_Generator::~RFC6979_Nonce_Generator() = default;

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

   m.serialize_to(std::span{m_rng_in}.subspan(m_rlen));

   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._assign_from_bytes(m_rng_out);

      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, std::string_view hash) {

   RFC6979_Nonce_Generator gen(hash, q, x);

   BigInt k = gen.nonce_for(h);

   return k;

}

}  // namespace Botan