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/*
* ECDSA implemenation
* (C) 2007 Manuel Hartl, FlexSecure GmbH
* 2007 Falko Strenzke, FlexSecure GmbH
* 2008-2010 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/pk_utils.h>
#include <botan/ecdsa.h>
#include <botan/reducer.h>
#include <botan/keypair.h>
#include <botan/rfc6979.h>
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
{
public:
typedef ECDSA_PrivateKey Key_Type;
ECDSA_Signature_Operation(const ECDSA_PrivateKey& ecdsa,
const std::string& emsa) :
base_point(ecdsa.domain().get_base_point()),
order(ecdsa.domain().get_order()),
x(ecdsa.private_value()),
mod_order(order),
m_hash(hash_for_deterministic_signature(emsa))
{
}
secure_vector<byte> sign(const byte msg[], size_t msg_len,
RandomNumberGenerator& rng);
size_t message_parts() const { return 2; }
size_t message_part_size() const { return order.bytes(); }
size_t max_input_bits() const { return order.bits(); }
private:
const PointGFp& base_point;
const BigInt& order;
const BigInt& x;
Modular_Reducer mod_order;
std::string m_hash;
};
secure_vector<byte>
ECDSA_Signature_Operation::sign(const byte msg[], size_t msg_len,
RandomNumberGenerator&)
{
const BigInt m(msg, msg_len);
const BigInt k = generate_rfc6979_nonce(x, order, m, m_hash);
const PointGFp k_times_P = base_point * k;
const BigInt r = mod_order.reduce(k_times_P.get_affine_x());
const BigInt s = mod_order.multiply(inverse_mod(k, order), mul_add(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*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
{
public:
typedef ECDSA_PublicKey Key_Type;
ECDSA_Verification_Operation(const ECDSA_PublicKey& ecdsa,
const std::string&) :
base_point(ecdsa.domain().get_base_point()),
public_point(ecdsa.public_point()),
order(ecdsa.domain().get_order())
{
}
size_t message_parts() const { return 2; }
size_t message_part_size() const { return order.bytes(); }
size_t max_input_bits() const { return order.bits(); }
bool with_recovery() const { return false; }
bool verify(const byte msg[], size_t msg_len,
const byte sig[], size_t sig_len);
private:
const PointGFp& base_point;
const PointGFp& public_point;
const BigInt& order;
};
bool ECDSA_Verification_Operation::verify(const byte msg[], size_t msg_len,
const byte sig[], size_t sig_len)
{
if(sig_len != 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 >= order || s <= 0 || s >= order)
return false;
BigInt w = inverse_mod(s, order);
PointGFp R = w * multi_exponentiate(base_point, e,
public_point, r);
if(R.is_zero())
return false;
return (R.get_affine_x() % order == r);
}
BOTAN_REGISTER_PK_SIGNATURE_OP("ECDSA", ECDSA_Signature_Operation);
BOTAN_REGISTER_PK_VERIFY_OP("ECDSA", ECDSA_Verification_Operation);
}
}
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