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/*
* ECDSA Operation
* (C) 2007 FlexSecure GmbH
* 2008-2010 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/ecdsa_op.h>
#include <botan/numthry.h>
namespace Botan {
Default_ECDSA_Op::Default_ECDSA_Op(const EC_Domain_Params& domain,
const BigInt& priv,
const PointGFp& pub) :
dom_pars(domain), pub_key(pub), priv_key(priv)
{
}
bool Default_ECDSA_Op::verify(const byte msg[], u32bit msg_len,
const byte sig[], u32bit sig_len) const
{
const BigInt& n = dom_pars.get_order();
if(sig_len != n.bytes()*2)
return false;
// NOTE: it is not checked whether the public point is set
if(dom_pars.get_curve().get_p() == 0)
throw Internal_Error("domain parameters not set");
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 * dom_pars.get_base_point() + r*pub_key);
if(R.is_zero())
return false;
BigInt x = R.get_affine_x();
return (x % n == r);
}
SecureVector<byte> Default_ECDSA_Op::sign(const byte msg[], u32bit msg_len,
const BigInt& k) const
{
if(priv_key == 0)
throw Internal_Error("Default_ECDSA_Op::sign(): no private key");
const BigInt& n = dom_pars.get_order();
if(n == 0)
throw Internal_Error("Default_ECDSA_Op::sign(): domain parameters not set");
BigInt e(msg, msg_len);
PointGFp k_times_P = dom_pars.get_base_point() * k;
k_times_P.check_invariants();
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);
s *= priv_key;
s += e;
s *= k_inv;
s %= 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;
}
}
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