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/*
* ECDSA implemenation
* (C) 2007 Manuel Hartl, FlexSecure GmbH
* 2007 Falko Strenzke, FlexSecure GmbH
* 2008-2010 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/ecdsa.h>
namespace Botan {
bool ECDSA_PublicKey::verify(const byte msg[], u32bit msg_len,
const byte sig[], u32bit sig_len) const
{
const BigInt& n = domain().get_order();
if(n == 0)
throw Invalid_State("ECDSA_PublicKey::verify: Not initialized");
if(sig_len != n.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 >= n || s < 0 || s >= n)
return false;
BigInt w = inverse_mod(s, n);
PointGFp R = w * (e * domain().get_base_point() + r*public_point());
if(R.is_zero())
return false;
return (R.get_affine_x() % n == r);
}
SecureVector<byte> ECDSA_PrivateKey::sign(const byte msg[],
u32bit msg_len,
RandomNumberGenerator& rng) const
{
const BigInt& n = domain().get_order();
if(n == 0 || private_value() == 0)
throw Invalid_State("ECDSA_PrivateKey::sign: Not initialized");
BigInt k;
do
k.randomize(rng, n.bits()-1);
while(k >= n);
BigInt e(msg, msg_len);
PointGFp k_times_P = domain().get_base_point() * k;
BigInt r = k_times_P.get_affine_x() % n;
if(r == 0)
throw Internal_Error("Default_ECDSA_Op::sign: r was zero");
BigInt k_inv = inverse_mod(k, n);
BigInt s = (((r * private_value()) + e) * k_inv) % n;
SecureVector<byte> output(2*n.bytes());
r.binary_encode(output + (output.size() / 2 - r.bytes()));
s.binary_encode(output + (output.size() - s.bytes()));
return output;
}
ECDSA_Signature_Operation::ECDSA_Signature_Operation(const ECDSA_PrivateKey& ecdsa) :
base_point(ecdsa.domain().get_base_point()),
order(ecdsa.domain().get_order()),
x(ecdsa.private_value())
{
}
SecureVector<byte> ECDSA_Signature_Operation::sign(const byte msg[],
u32bit msg_len,
RandomNumberGenerator& rng)
{
rng.add_entropy(msg, msg_len);
BigInt k;
do
k.randomize(rng, order.bits()-1);
while(k >= order);
BigInt e(msg, msg_len);
PointGFp k_times_P = base_point * k;
BigInt r = k_times_P.get_affine_x() % order;
if(r == 0)
throw Internal_Error("ECDSA_Signature_Operation: r was zero");
BigInt k_inv = inverse_mod(k, order);
BigInt s = (((r * x) + e) * k_inv) % order;
SecureVector<byte> output(2*order.bytes());
r.binary_encode(output + (output.size() / 2 - r.bytes()));
s.binary_encode(output + (output.size() - s.bytes()));
return output;
}
}
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