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/*
* DSA
* (C) 1999-2010,2014 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/dsa.h>
#include <botan/numthry.h>
#include <botan/keypair.h>
#include <botan/rfc6979.h>
#include <future>
namespace Botan {
/*
* DSA_PublicKey Constructor
*/
DSA_PublicKey::DSA_PublicKey(const DL_Group& grp, const BigInt& y1)
{
group = grp;
y = y1;
}
/*
* Create a DSA private key
*/
DSA_PrivateKey::DSA_PrivateKey(RandomNumberGenerator& rng,
const DL_Group& grp,
const BigInt& x_arg)
{
group = grp;
x = x_arg;
if(x == 0)
x = BigInt::random_integer(rng, 2, group_q() - 1);
y = power_mod(group_g(), x, group_p());
if(x_arg == 0)
gen_check(rng);
else
load_check(rng);
}
DSA_PrivateKey::DSA_PrivateKey(const AlgorithmIdentifier& alg_id,
const secure_vector<byte>& key_bits,
RandomNumberGenerator& rng) :
DL_Scheme_PrivateKey(alg_id, key_bits, DL_Group::ANSI_X9_57)
{
y = power_mod(group_g(), x, group_p());
load_check(rng);
}
/*
* Check Private DSA Parameters
*/
bool DSA_PrivateKey::check_key(RandomNumberGenerator& rng, bool strong) const
{
if(!DL_Scheme_PrivateKey::check_key(rng, strong) || x >= group_q())
return false;
if(!strong)
return true;
return KeyPair::signature_consistency_check(rng, *this, "EMSA1(SHA-1)");
}
DSA_Signature_Operation::DSA_Signature_Operation(const DSA_PrivateKey& dsa,
const std::string& emsa) :
q(dsa.group_q()),
x(dsa.get_x()),
powermod_g_p(dsa.group_g(), dsa.group_p()),
mod_q(dsa.group_q()),
m_hash(hash_for_deterministic_signature(emsa))
{
}
secure_vector<byte>
DSA_Signature_Operation::sign(const byte msg[], size_t msg_len,
RandomNumberGenerator&)
{
BigInt i(msg, msg_len);
while(i >= q)
i -= q;
const BigInt k = generate_rfc6979_nonce(x, q, i, m_hash);
auto future_r = std::async(std::launch::async,
[&]() { return mod_q.reduce(powermod_g_p(k)); });
BigInt s = inverse_mod(k, q);
const BigInt r = future_r.get();
s = mod_q.multiply(s, mul_add(x, r, i));
// With overwhelming probability, a bug rather than actual zero r/s
BOTAN_ASSERT(s != 0, "invalid s");
BOTAN_ASSERT(r != 0, "invalid r");
secure_vector<byte> output(2*q.bytes());
r.binary_encode(&output[output.size() / 2 - r.bytes()]);
s.binary_encode(&output[output.size() - s.bytes()]);
return output;
}
DSA_Verification_Operation::DSA_Verification_Operation(const DSA_PublicKey& dsa) :
q(dsa.group_q()), y(dsa.get_y())
{
powermod_g_p = Fixed_Base_Power_Mod(dsa.group_g(), dsa.group_p());
powermod_y_p = Fixed_Base_Power_Mod(y, dsa.group_p());
mod_p = Modular_Reducer(dsa.group_p());
mod_q = Modular_Reducer(dsa.group_q());
}
bool DSA_Verification_Operation::verify(const byte msg[], size_t msg_len,
const byte sig[], size_t sig_len)
{
if(sig_len != 2*q.bytes() || msg_len > q.bytes())
return false;
BigInt r(sig, q.bytes());
BigInt s(sig + q.bytes(), q.bytes());
BigInt i(msg, msg_len);
if(r <= 0 || r >= q || s <= 0 || s >= q)
return false;
s = inverse_mod(s, q);
auto future_s_i = std::async(std::launch::async,
[&]() { return powermod_g_p(mod_q.multiply(s, i)); });
BigInt s_r = powermod_y_p(mod_q.multiply(s, r));
BigInt s_i = future_s_i.get();
s = mod_p.multiply(s_i, s_r);
return (mod_q.reduce(s) == r);
}
}
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