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/*
* ECDSA implemenation
* (C) 2007 Manuel Hartl, FlexSecure GmbH
* 2007 Falko Strenzke, FlexSecure GmbH
* 2008-2010,2015,2016,2018 Jack Lloyd
* 2016 René Korthaus
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/ecdsa.h>
#include <botan/internal/pk_ops_impl.h>
#include <botan/internal/point_mul.h>
#include <botan/keypair.h>
#include <botan/reducer.h>
#include <botan/emsa.h>
#if defined(BOTAN_HAS_RFC6979_GENERATOR)
#include <botan/rfc6979.h>
#endif
#if defined(BOTAN_HAS_BEARSSL)
#include <botan/internal/bearssl.h>
#endif
#if defined(BOTAN_HAS_OPENSSL)
#include <botan/internal/openssl.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-256)");
}
namespace {
/**
* ECDSA signature operation
*/
class ECDSA_Signature_Operation final : public PK_Ops::Signature_with_EMSA
{
public:
ECDSA_Signature_Operation(const ECDSA_PrivateKey& ecdsa,
const std::string& emsa,
RandomNumberGenerator& rng) :
PK_Ops::Signature_with_EMSA(emsa),
m_group(ecdsa.domain()),
m_x(ecdsa.private_value())
{
#if defined(BOTAN_HAS_RFC6979_GENERATOR)
m_rfc6979_hash = hash_for_emsa(emsa);
#endif
m_b = m_group.random_scalar(rng);
m_b_inv = m_group.inverse_mod_order(m_b);
}
size_t max_input_bits() const override { return m_group.get_order_bits(); }
secure_vector<uint8_t> raw_sign(const uint8_t msg[], size_t msg_len,
RandomNumberGenerator& rng) override;
private:
const EC_Group m_group;
const BigInt& m_x;
#if defined(BOTAN_HAS_RFC6979_GENERATOR)
std::string m_rfc6979_hash;
#endif
std::vector<BigInt> m_ws;
BigInt m_b, m_b_inv;
};
secure_vector<uint8_t>
ECDSA_Signature_Operation::raw_sign(const uint8_t msg[], size_t msg_len,
RandomNumberGenerator& rng)
{
BigInt m(msg, msg_len, m_group.get_order_bits());
#if defined(BOTAN_HAS_RFC6979_GENERATOR)
const BigInt k = generate_rfc6979_nonce(m_x, m_group.get_order(), m, m_rfc6979_hash);
#else
const BigInt k = m_group.random_scalar(rng);
#endif
const BigInt r = m_group.mod_order(
m_group.blinded_base_point_multiply_x(k, rng, m_ws));
const BigInt k_inv = m_group.inverse_mod_order(k);
/*
* Blind the input message and compute x*r+m as (x*r*b + m*b)/b
*/
m_b = m_group.square_mod_order(m_b);
m_b_inv = m_group.square_mod_order(m_b_inv);
m = m_group.multiply_mod_order(m_b, m);
const BigInt xr = m_group.multiply_mod_order(m_x, m_b, r);
const BigInt s = m_group.multiply_mod_order(k_inv, xr + m, m_b_inv);
// With overwhelming probability, a bug rather than actual zero r/s
if(r.is_zero() || s.is_zero())
throw Internal_Error("During ECDSA signature generated zero r/s");
return BigInt::encode_fixed_length_int_pair(r, s, m_group.get_order_bytes());
}
/**
* ECDSA verification operation
*/
class ECDSA_Verification_Operation final : public PK_Ops::Verification_with_EMSA
{
public:
ECDSA_Verification_Operation(const ECDSA_PublicKey& ecdsa,
const std::string& emsa) :
PK_Ops::Verification_with_EMSA(emsa),
m_group(ecdsa.domain()),
m_gy_mul(m_group.get_base_point(), ecdsa.public_point())
{
}
size_t max_input_bits() const override { return m_group.get_order_bits(); }
bool with_recovery() const override { return false; }
bool verify(const uint8_t msg[], size_t msg_len,
const uint8_t sig[], size_t sig_len) override;
private:
const EC_Group m_group;
const PointGFp_Multi_Point_Precompute m_gy_mul;
};
bool ECDSA_Verification_Operation::verify(const uint8_t msg[], size_t msg_len,
const uint8_t sig[], size_t sig_len)
{
if(sig_len != m_group.get_order_bytes() * 2)
return false;
const BigInt e(msg, msg_len, m_group.get_order_bits());
const BigInt r(sig, sig_len / 2);
const BigInt s(sig + sig_len / 2, sig_len / 2);
if(r <= 0 || r >= m_group.get_order() || s <= 0 || s >= m_group.get_order())
return false;
const BigInt w = m_group.inverse_mod_order(s);
const BigInt u1 = m_group.multiply_mod_order(m_group.mod_order(e), w);
const BigInt u2 = m_group.multiply_mod_order(r, w);
const PointGFp R = m_gy_mul.multi_exp(u1, u2);
if(R.is_zero())
return false;
const BigInt v = m_group.mod_order(R.get_affine_x());
return (v == r);
}
}
std::unique_ptr<PK_Ops::Verification>
ECDSA_PublicKey::create_verification_op(const std::string& params,
const std::string& provider) const
{
#if defined(BOTAN_HAS_BEARSSL)
if(provider == "bearssl" || provider.empty())
{
try
{
return make_bearssl_ecdsa_ver_op(*this, params);
}
catch(Lookup_Error& e)
{
if(provider == "bearssl")
throw;
}
}
#endif
#if defined(BOTAN_HAS_OPENSSL)
if(provider == "openssl" || provider.empty())
{
try
{
return make_openssl_ecdsa_ver_op(*this, params);
}
catch(Lookup_Error& e)
{
if(provider == "openssl")
throw;
}
}
#endif
if(provider == "base" || provider.empty())
return std::unique_ptr<PK_Ops::Verification>(new ECDSA_Verification_Operation(*this, params));
throw Provider_Not_Found(algo_name(), provider);
}
std::unique_ptr<PK_Ops::Signature>
ECDSA_PrivateKey::create_signature_op(RandomNumberGenerator& rng,
const std::string& params,
const std::string& provider) const
{
#if defined(BOTAN_HAS_BEARSSL)
if(provider == "bearssl" || provider.empty())
{
try
{
return make_bearssl_ecdsa_sig_op(*this, params);
}
catch(Lookup_Error& e)
{
if(provider == "bearssl")
throw;
}
}
#endif
#if defined(BOTAN_HAS_OPENSSL)
if(provider == "openssl" || provider.empty())
{
try
{
return make_openssl_ecdsa_sig_op(*this, params);
}
catch(Lookup_Error& e)
{
if(provider == "openssl")
throw;
}
}
#endif
if(provider == "base" || provider.empty())
return std::unique_ptr<PK_Ops::Signature>(new ECDSA_Signature_Operation(*this, params, rng));
throw Provider_Not_Found(algo_name(), provider);
}
}
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