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/*
* DSA
* (C) 1999-2010,2014 Jack Lloyd
* (C) 2016 René Korthaus
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/pk_utils.h>
#include <botan/dsa.h>
#include <botan/keypair.h>
#include <botan/pow_mod.h>
#include <botan/reducer.h>
#if defined(BOTAN_HAS_RFC6979_GENERATOR)
#include <botan/rfc6979.h>
#include <botan/emsa.h>
#endif
#include <future>
namespace Botan {
/*
* DSA_PublicKey Constructor
*/
DSA_PublicKey::DSA_PublicKey(const DL_Group& grp, const BigInt& y1)
{
m_group = grp;
m_y = y1;
}
/*
* Create a DSA private key
*/
DSA_PrivateKey::DSA_PrivateKey(RandomNumberGenerator& rng,
const DL_Group& grp,
const BigInt& x_arg)
{
m_group = grp;
m_x = x_arg;
if(m_x == 0)
m_x = BigInt::random_integer(rng, 2, group_q() - 1);
m_y = power_mod(group_g(), m_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)
{
m_y = power_mod(group_g(), m_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) || m_x >= group_q())
return false;
if(!strong)
return true;
return KeyPair::signature_consistency_check(rng, *this, "EMSA1(SHA-256)");
}
namespace {
/**
* Object that can create a DSA signature
*/
class DSA_Signature_Operation : public PK_Ops::Signature_with_EMSA
{
public:
typedef DSA_PrivateKey Key_Type;
DSA_Signature_Operation(const DSA_PrivateKey& dsa, const std::string& emsa) :
PK_Ops::Signature_with_EMSA(emsa),
m_q(dsa.group_q()),
m_x(dsa.get_x()),
m_powermod_g_p(dsa.group_g(), dsa.group_p()),
m_mod_q(dsa.group_q()),
m_emsa(emsa)
{
}
size_t message_parts() const override { return 2; }
size_t message_part_size() const override { return m_q.bytes(); }
size_t max_input_bits() const override { return m_q.bits(); }
secure_vector<byte> raw_sign(const byte msg[], size_t msg_len,
RandomNumberGenerator& rng) override;
private:
const BigInt& m_q;
const BigInt& m_x;
Fixed_Base_Power_Mod m_powermod_g_p;
Modular_Reducer m_mod_q;
std::string m_emsa;
};
secure_vector<byte>
DSA_Signature_Operation::raw_sign(const byte msg[], size_t msg_len,
RandomNumberGenerator& rng)
{
BigInt i(msg, msg_len);
while(i >= m_q)
i -= m_q;
#if defined(BOTAN_HAS_RFC6979_GENERATOR)
const BigInt k = generate_rfc6979_nonce(m_x, m_q, i, hash_for_emsa(m_emsa));
#else
const BigInt k = BigInt::random_integer(rng, 1, m_q);
#endif
auto future_r = std::async(std::launch::async,
[&]() { return m_mod_q.reduce(m_powermod_g_p(k)); });
BigInt s = inverse_mod(k, m_q);
const BigInt r = future_r.get();
s = m_mod_q.multiply(s, mul_add(m_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*m_q.bytes());
r.binary_encode(&output[output.size() / 2 - r.bytes()]);
s.binary_encode(&output[output.size() - s.bytes()]);
return output;
}
/**
* Object that can verify a DSA signature
*/
class DSA_Verification_Operation : public PK_Ops::Verification_with_EMSA
{
public:
typedef DSA_PublicKey Key_Type;
DSA_Verification_Operation(const DSA_PublicKey& dsa,
const std::string& emsa) :
PK_Ops::Verification_with_EMSA(emsa),
m_q(dsa.group_q()), m_y(dsa.get_y()), m_powermod_g_p{Fixed_Base_Power_Mod(dsa.group_g(), dsa.group_p())},
m_powermod_y_p{Fixed_Base_Power_Mod(m_y, dsa.group_p())}, m_mod_p{Modular_Reducer(dsa.group_p())},
m_mod_q{Modular_Reducer(dsa.group_q())}
{}
size_t message_parts() const override { return 2; }
size_t message_part_size() const override { return m_q.bytes(); }
size_t max_input_bits() const override { return m_q.bits(); }
bool with_recovery() const override { return false; }
bool verify(const byte msg[], size_t msg_len,
const byte sig[], size_t sig_len) override;
private:
const BigInt& m_q;
const BigInt& m_y;
Fixed_Base_Power_Mod m_powermod_g_p, m_powermod_y_p;
Modular_Reducer m_mod_p, m_mod_q;
};
bool DSA_Verification_Operation::verify(const byte msg[], size_t msg_len,
const byte sig[], size_t sig_len)
{
if(sig_len != 2*m_q.bytes() || msg_len > m_q.bytes())
return false;
BigInt r(sig, m_q.bytes());
BigInt s(sig + m_q.bytes(), m_q.bytes());
BigInt i(msg, msg_len);
if(r <= 0 || r >= m_q || s <= 0 || s >= m_q)
return false;
s = inverse_mod(s, m_q);
auto future_s_i = std::async(std::launch::async,
[&]() { return m_powermod_g_p(m_mod_q.multiply(s, i)); });
BigInt s_r = m_powermod_y_p(m_mod_q.multiply(s, r));
BigInt s_i = future_s_i.get();
s = m_mod_p.multiply(s_i, s_r);
return (m_mod_q.reduce(s) == r);
}
BOTAN_REGISTER_PK_SIGNATURE_OP("DSA", DSA_Signature_Operation);
BOTAN_REGISTER_PK_VERIFY_OP("DSA", DSA_Verification_Operation);
}
}
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