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/*
* ECKCDSA (ISO/IEC 14888-3:2006/Cor.2:2009)
* (C) 2016 René Korthaus, Sirrix AG
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/eckcdsa.h>
#include <botan/internal/pk_ops_impl.h>
#include <botan/keypair.h>
#include <botan/reducer.h>
#include <botan/emsa.h>
#include <botan/hash.h>
namespace Botan {
bool ECKCDSA_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 {
/**
* ECKCDSA signature operation
*/
class ECKCDSA_Signature_Operation : public PK_Ops::Signature_with_EMSA
{
public:
typedef ECKCDSA_PrivateKey Key_Type;
ECKCDSA_Signature_Operation(const ECKCDSA_PrivateKey& eckcdsa,
const std::string& emsa) :
PK_Ops::Signature_with_EMSA(emsa),
m_order(eckcdsa.domain().get_order()),
m_base_point(eckcdsa.domain().get_base_point(), m_order),
m_x(eckcdsa.private_value()),
m_mod_order(m_order),
m_prefix()
{
const BigInt public_point_x = eckcdsa.public_point().get_affine_x();
const BigInt public_point_y = eckcdsa.public_point().get_affine_y();
m_prefix.resize(public_point_x.bytes() + public_point_y.bytes());
public_point_x.binary_encode(m_prefix.data());
public_point_y.binary_encode(&m_prefix[public_point_x.bytes()]);
m_prefix.resize(HashFunction::create(hash_for_signature())->hash_block_size()); // use only the "hash input block size" leftmost bits
}
secure_vector<byte> raw_sign(const byte msg[], size_t msg_len,
RandomNumberGenerator& rng) override;
size_t message_parts() const override { return 2; }
size_t message_part_size() const override { return m_order.bytes(); }
size_t max_input_bits() const override { return m_order.bits(); }
bool has_prefix() override { return true; }
secure_vector<byte> message_prefix() const override { return m_prefix; }
private:
const BigInt& m_order;
Blinded_Point_Multiply m_base_point;
const BigInt& m_x;
Modular_Reducer m_mod_order;
secure_vector<byte> m_prefix;
};
secure_vector<byte>
ECKCDSA_Signature_Operation::raw_sign(const byte msg[], size_t,
RandomNumberGenerator& rng)
{
const BigInt k = BigInt::random_integer(rng, 1, m_order);
const PointGFp k_times_P = m_base_point.blinded_multiply(k, rng);
const BigInt k_times_P_x = k_times_P.get_affine_x();
secure_vector<byte> to_be_hashed(k_times_P_x.bytes());
k_times_P_x.binary_encode(to_be_hashed.data());
std::unique_ptr<EMSA> emsa(m_emsa->clone());
emsa->update(to_be_hashed.data(), to_be_hashed.size());
secure_vector<byte> c = emsa->raw_data();
c = emsa->encoding_of(c, max_input_bits(), rng);
const BigInt r(c.data(), c.size());
xor_buf(c, msg, c.size());
BigInt w(c.data(), c.size());
w = m_mod_order.reduce(w);
const BigInt s = m_mod_order.multiply(m_x, k - w);
BOTAN_ASSERT(s != 0, "invalid s");
secure_vector<byte> output = BigInt::encode_1363(r, c.size());
output += BigInt::encode_1363(s, m_mod_order.get_modulus().bytes());
return output;
}
/**
* ECKCDSA verification operation
*/
class ECKCDSA_Verification_Operation : public PK_Ops::Verification_with_EMSA
{
public:
typedef ECKCDSA_PublicKey Key_Type;
ECKCDSA_Verification_Operation(const ECKCDSA_PublicKey& eckcdsa,
const std::string& emsa) :
PK_Ops::Verification_with_EMSA(emsa),
m_base_point(eckcdsa.domain().get_base_point()),
m_public_point(eckcdsa.public_point()),
m_order(eckcdsa.domain().get_order()),
m_mod_order(m_order),
m_prefix()
{
const BigInt public_point_x = m_public_point.get_affine_x();
const BigInt public_point_y = m_public_point.get_affine_y();
m_prefix.resize(public_point_x.bytes() + public_point_y.bytes());
public_point_x.binary_encode(&m_prefix[0]);
public_point_y.binary_encode(&m_prefix[public_point_x.bytes()]);
m_prefix.resize(HashFunction::create(hash_for_signature())->hash_block_size()); // use only the "hash input block size" leftmost bits
}
bool has_prefix() override { return true; }
secure_vector<byte> message_prefix() const override { return m_prefix; }
size_t message_parts() const override { return 2; }
size_t message_part_size() const override { return m_order.bytes(); }
size_t max_input_bits() const override { return m_order.bits(); }
bool with_recovery() const override { return false; }
bool verify(const byte msg[], size_t msg_len,
const byte sig[], size_t sig_len) override;
private:
const PointGFp& m_base_point;
const PointGFp& m_public_point;
const BigInt& m_order;
// FIXME: should be offered by curve
Modular_Reducer m_mod_order;
secure_vector<byte> m_prefix;
};
bool ECKCDSA_Verification_Operation::verify(const byte msg[], size_t,
const byte sig[], size_t sig_len)
{
// check that bit length of r is equal to output bit length of employed hash function h
const std::unique_ptr<HashFunction> hash = HashFunction::create(hash_for_signature());
// no way to know size of r in sig, so check that we have at least hash->output_length()+1
// bytes in sig, enough for r and an arbitrary size s
if(sig_len <= hash->output_length())
{
return false;
}
secure_vector<byte> r(sig, sig + hash->output_length());
// check that 0 < s < q
const BigInt s(sig + hash->output_length(), sig_len - hash->output_length());
if(s <= 0 || s >= m_order)
{
return false;
}
secure_vector<byte> r_xor_e(r);
xor_buf(r_xor_e, msg, r.size());
BigInt w(r_xor_e.data(), r_xor_e.size());
w = m_mod_order.reduce(w);
const PointGFp q = (m_base_point * w) + (m_public_point * s);
const BigInt q_x = q.get_affine_x();
secure_vector<byte> c(q_x.bytes());
q_x.binary_encode(c.data());
std::unique_ptr<EMSA> emsa(m_emsa->clone());
emsa->update(c.data(), c.size());
secure_vector<byte> v = emsa->raw_data();
Null_RNG rng;
v = emsa->encoding_of(v, max_input_bits(), rng);
return (v == r);
}
}
std::unique_ptr<PK_Ops::Verification>
ECKCDSA_PublicKey::create_verification_op(const std::string& params,
const std::string& provider) const
{
if(provider == "base" || provider.empty())
return std::unique_ptr<PK_Ops::Verification>(new ECKCDSA_Verification_Operation(*this, params));
throw Provider_Not_Found(algo_name(), provider);
}
std::unique_ptr<PK_Ops::Signature>
ECKCDSA_PrivateKey::create_signature_op(RandomNumberGenerator& /*rng*/,
const std::string& params,
const std::string& provider) const
{
if(provider == "base" || provider.empty())
return std::unique_ptr<PK_Ops::Signature>(new ECKCDSA_Signature_Operation(*this, params));
throw Provider_Not_Found(algo_name(), provider);
}
}
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