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/*
* ECGDSA (BSI-TR-03111, version 2.0)
* (C) 2016 René Korthaus
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/ecgdsa.h>
#include <botan/keypair.h>
#include <botan/reducer.h>
#include <botan/internal/pk_ops_impl.h>
namespace Botan {
bool ECGDSA_PrivateKey::check_key(RandomNumberGenerator& rng,
bool strong) const
{
if(!public_point().on_the_curve())
return false;
if(!strong)
return true;
return KeyPair::signature_consistency_check(rng, *this, "EMSA1(SHA-256)");
}
namespace {
/**
* ECGDSA signature operation
*/
class ECGDSA_Signature_Operation : public PK_Ops::Signature_with_EMSA
{
public:
typedef ECGDSA_PrivateKey Key_Type;
ECGDSA_Signature_Operation(const ECGDSA_PrivateKey& ecgdsa,
const std::string& emsa) :
PK_Ops::Signature_with_EMSA(emsa),
m_order(ecgdsa.domain().get_order()),
m_base_point(ecgdsa.domain().get_base_point(), m_order),
m_x(ecgdsa.private_value()),
m_mod_order(m_order)
{
}
secure_vector<byte> raw_sign(const byte msg[], size_t msg_len,
RandomNumberGenerator& rng) override;
size_t message_parts() const override { return 2; }
size_t message_part_size() const override { return m_order.bytes(); }
size_t max_input_bits() const override { return m_order.bits(); }
private:
const BigInt& m_order;
Blinded_Point_Multiply m_base_point;
const BigInt& m_x;
Modular_Reducer m_mod_order;
};
secure_vector<byte>
ECGDSA_Signature_Operation::raw_sign(const byte msg[], size_t msg_len,
RandomNumberGenerator& rng)
{
const BigInt m(msg, msg_len);
BigInt k = BigInt::random_integer(rng, 1, m_order);
const PointGFp k_times_P = m_base_point.blinded_multiply(k, rng);
const BigInt r = m_mod_order.reduce(k_times_P.get_affine_x());
const BigInt s = m_mod_order.multiply(m_x, mul_sub(k, r, m));
// With overwhelming probability, a bug rather than actual zero r/s
BOTAN_ASSERT(s != 0, "invalid s");
BOTAN_ASSERT(r != 0, "invalid r");
return BigInt::encode_fixed_length_int_pair(r, s, m_order.bytes());
}
/**
* ECGDSA verification operation
*/
class ECGDSA_Verification_Operation : public PK_Ops::Verification_with_EMSA
{
public:
typedef ECGDSA_PublicKey Key_Type;
ECGDSA_Verification_Operation(const ECGDSA_PublicKey& ecgdsa,
const std::string& emsa) :
PK_Ops::Verification_with_EMSA(emsa),
m_base_point(ecgdsa.domain().get_base_point()),
m_public_point(ecgdsa.public_point()),
m_order(ecgdsa.domain().get_order()),
m_mod_order(m_order)
{
}
size_t message_parts() const override { return 2; }
size_t message_part_size() const override { return m_order.bytes(); }
size_t max_input_bits() const override { return m_order.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 PointGFp& m_base_point;
const PointGFp& m_public_point;
const BigInt& m_order;
// FIXME: should be offered by curve
Modular_Reducer m_mod_order;
};
bool ECGDSA_Verification_Operation::verify(const byte msg[], size_t msg_len,
const byte sig[], size_t sig_len)
{
if(sig_len != m_order.bytes()*2)
return false;
BigInt e(msg, msg_len);
BigInt r(sig, sig_len / 2);
BigInt s(sig + sig_len / 2, sig_len / 2);
if(r <= 0 || r >= m_order || s <= 0 || s >= m_order)
return false;
BigInt w = inverse_mod(r, m_order);
const BigInt u1 = m_mod_order.reduce(e * w);
const BigInt u2 = m_mod_order.reduce(s * w);
const PointGFp R = multi_exponentiate(m_base_point, u1, m_public_point, u2);
if(R.is_zero())
return false;
const BigInt v = m_mod_order.reduce(R.get_affine_x());
return (v == r);
}
}
std::unique_ptr<PK_Ops::Verification>
ECGDSA_PublicKey::create_verification_op(const std::string& params,
const std::string& provider) const
{
if(provider == "base" || provider.empty())
return std::unique_ptr<PK_Ops::Verification>(new ECGDSA_Verification_Operation(*this, params));
throw Provider_Not_Found(algo_name(), provider);
}
std::unique_ptr<PK_Ops::Signature>
ECGDSA_PrivateKey::create_signature_op(RandomNumberGenerator& /*rng*/,
const std::string& params,
const std::string& provider) const
{
if(provider == "base" || provider.empty())
return std::unique_ptr<PK_Ops::Signature>(new ECGDSA_Signature_Operation(*this, params));
throw Provider_Not_Found(algo_name(), provider);
}
}
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