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/*
* ECDSA implemenation
* (C) 2007 Manuel Hartl, FlexSecure GmbH
* 2007 Falko Strenzke, FlexSecure GmbH
* 2008-2010,2015 Jack Lloyd
* 2016 René Korthaus
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/pk_utils.h>
#include <botan/ecdsa.h>
#include <botan/keypair.h>
#if defined(BOTAN_HAS_RFC6979_GENERATOR)
#include <botan/rfc6979.h>
#include <botan/emsa.h>
#endif
namespace Botan {
bool ECDSA_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-1)");
}
namespace {
/**
* ECDSA signature operation
*/
class ECDSA_Signature_Operation : public PK_Ops::Signature_with_EMSA
{
public:
typedef ECDSA_PrivateKey Key_Type;
ECDSA_Signature_Operation(const ECDSA_PrivateKey& ecdsa,
const std::string& emsa) :
PK_Ops::Signature_with_EMSA(emsa),
m_order(ecdsa.domain().get_order()),
m_base_point(ecdsa.domain().get_base_point(), m_order),
m_x(ecdsa.private_value()),
m_mod_order(m_order),
m_emsa(emsa)
{
}
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;
std::string m_emsa;
};
secure_vector<byte>
ECDSA_Signature_Operation::raw_sign(const byte msg[], size_t msg_len,
RandomNumberGenerator& rng)
{
const BigInt m(msg, msg_len);
#if defined(BOTAN_HAS_RFC6979_GENERATOR)
const BigInt k = generate_rfc6979_nonce(m_x, m_order, m, hash_for_emsa(m_emsa));
#else
const BigInt k = BigInt::random_integer(rng, 1, m_order);
#endif
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(inverse_mod(k, m_order), mul_add(m_x, 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");
secure_vector<byte> output(2*m_order.bytes());
r.binary_encode(&output[output.size() / 2 - r.bytes()]);
s.binary_encode(&output[output.size() - s.bytes()]);
return output;
}
/**
* ECDSA verification operation
*/
class ECDSA_Verification_Operation : public PK_Ops::Verification_with_EMSA
{
public:
typedef ECDSA_PublicKey Key_Type;
ECDSA_Verification_Operation(const ECDSA_PublicKey& ecdsa,
const std::string& emsa) :
PK_Ops::Verification_with_EMSA(emsa),
m_base_point(ecdsa.domain().get_base_point()),
m_public_point(ecdsa.public_point()),
m_order(ecdsa.domain().get_order()),
m_mod_order(m_order)
{
//m_public_point.precompute_multiples();
}
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 ECDSA_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(s, m_order);
const BigInt u1 = m_mod_order.reduce(e * w);
const BigInt u2 = m_mod_order.reduce(r * 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);
}
BOTAN_REGISTER_PK_SIGNATURE_OP("ECDSA", ECDSA_Signature_Operation);
BOTAN_REGISTER_PK_VERIFY_OP("ECDSA", ECDSA_Verification_Operation);
}
}
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