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/*
* RFC 6979 Deterministic Nonce Generator
* (C) 2014,2015 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/rfc6979.h>
#include <botan/hmac_drbg.h>
#include <botan/scan_name.h>
#include <botan/lookup.h>
namespace Botan {
std::string hash_for_deterministic_signature(const std::string& emsa)
{
SCAN_Name emsa_name(emsa);
if(emsa_name.arg_count() > 0)
{
const std::string pos_hash = emsa_name.arg(0);
return pos_hash;
}
return "SHA-512"; // safe default if nothing we understand
}
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_hmac_drbg(new HMAC_DRBG(make_message_auth("HMAC(" + hash + ")").release())),
m_rng_in(m_rlen * 2),
m_rng_out(m_rlen)
{
BigInt::encode_1363(&m_rng_in[0], m_rlen, x);
}
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->add_entropy(&m_rng_in[0], m_rng_in.size());
do
{
m_hmac_drbg->randomize(&m_rng_out[0], m_rng_out.size());
m_k.binary_decode(&m_rng_out[0], 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;
}
}
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