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/*************************************************
* ECDSA Operation *
* (C) 2007 FlexSecure GmbH *
* 2008 Jack Lloyd *
*************************************************/
#include <botan/eng_def.h>
namespace Botan {
bool Default_ECDSA_Op::verify(const byte signature[], u32bit sig_len,
const byte message[], u32bit mess_len) const
{
if(sig_len % 2 != 0)
throw Invalid_Argument("Erroneous length of signature");
//NOTE: it is not checked whether the public point is set
if(m_dom_pars.get_curve().get_p() == 0)
throw Internal_Error("domain parameters not set");
BigInt e(message, mess_len);
u32bit rs_len = sig_len/2;
SecureVector<byte> sv_r;
SecureVector<byte> sv_s;
sv_r.set(signature, rs_len);
sv_s.set(signature+rs_len, rs_len);
BigInt r = BigInt::decode ( sv_r, sv_r.size());
BigInt s = BigInt::decode (sv_s, sv_s.size());
if(r < 0 || r >= m_dom_pars.get_order())
throw Invalid_Argument("r in ECDSA signature has an illegal value");
if(s < 0 || s >= m_dom_pars.get_order())
throw Invalid_Argument("s in ECDSA signature has an illegal value");
BigInt w = inverse_mod(s, m_dom_pars.get_order());
PointGFp R = w*(e*m_dom_pars.get_base_point() + r*m_pub_key);
if(R.is_zero())
return false;
BigInt x = R.get_affine_x().get_value();
bool result = (x % m_dom_pars.get_order() == r);
return result;
}
SecureVector<byte> Default_ECDSA_Op::sign(const byte message[],
u32bit mess_len,
RandomNumberGenerator& rng) const
{
if(m_priv_key == 0)
throw Internal_Error("Default_ECDSA_Op::sign(): no private key");
if(m_dom_pars.get_curve().get_p() == 0)
throw Internal_Error("Default_ECDSA_Op::sign(): domain parameters not set");
BigInt e(message, mess_len);
// generate k
BigInt k;
BigInt r(0);
const BigInt n(m_dom_pars.get_order());
while(r == 0)
{
k = BigInt::random_integer(rng, 1, n);
PointGFp k_times_P(m_dom_pars.get_base_point());
k_times_P.mult_this_secure(k, n, n-1);
k_times_P.check_invariants();
r = k_times_P.get_affine_x().get_value() % n;
}
BigInt k_inv = inverse_mod(k, n);
// use randomization against attacks on s:
// a = k_inv * (r*(d + x) + e) mod n
// b = k_inv * r * x mod n
// s = a - b mod n
// where x is a random integer
#ifdef CMS_RAND
BigInt x = Botan::random_integer(0, n);
BigInt s = m_priv_key + x; // obscure the secret from the beginning
// all following operations thus are randomized
s *= r;
s += e;
s *= k_inv;
s %= n;
BigInt b = x; // again, start with the random number
b *= r;
b *= k_inv;
b %= n;
s -= b; // s = a - b
if(s <= 0) // s %= n
{
s += n;
}
#else // CMS_RAND
// no countermeasure here
BigInt s(r);
s *= m_priv_key;
s += e;
s *= k_inv;
s %= n;
#endif // CMS_RAND
SecureVector<byte> sv_r = BigInt::encode_1363 ( r, m_dom_pars.get_order().bytes() );
SecureVector<byte> sv_s = BigInt::encode_1363 ( s, m_dom_pars.get_order().bytes() );
SecureVector<byte> result(sv_r);
result.append(sv_s);
return result;
}
Default_ECDSA_Op::Default_ECDSA_Op(const EC_Domain_Params& dom_pars, const BigInt& priv_key, const PointGFp& pub_key)
: m_dom_pars(dom_pars),
m_pub_key(pub_key),
m_priv_key(priv_key)
{
}
/*************************************************
* Acquire a ECDSA op *
*************************************************/
ECDSA_Operation* Default_Engine::ecdsa_op(const EC_Domain_Params& dom_pars,
const BigInt& priv_key,
const PointGFp& pub_key) const
{
return new Default_ECDSA_Op(dom_pars, priv_key, pub_key);
}
}
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