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/*
* SM2 Encryption
* (C) 2017 Ribose Inc
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/sm2_enc.h>
#include <botan/pk_ops.h>
#include <botan/keypair.h>
#include <botan/kdf.h>
#include <botan/hash.h>
namespace Botan {
bool SM2_Encryption_PrivateKey::check_key(RandomNumberGenerator& rng,
bool strong) const
{
if(!public_point().on_the_curve())
return false;
if(!strong)
return true;
return KeyPair::encryption_consistency_check(rng, *this, "SM3");
}
SM2_Encryption_PrivateKey::SM2_Encryption_PrivateKey(const AlgorithmIdentifier& alg_id,
const secure_vector<uint8_t>& key_bits) :
EC_PrivateKey(alg_id, key_bits)
{
}
SM2_Encryption_PrivateKey::SM2_Encryption_PrivateKey(RandomNumberGenerator& rng,
const EC_Group& domain,
const BigInt& x) :
EC_PrivateKey(rng, domain, x)
{
}
namespace {
class SM2_Encryption_Operation : public PK_Ops::Encryption
{
public:
SM2_Encryption_Operation(const SM2_Encryption_PublicKey& key, const std::string& kdf_hash) :
m_p_bytes(key.domain().get_curve().get_p().bytes()),
m_order(key.domain().get_order()),
m_base_point(key.domain().get_base_point(), m_order),
m_public_point(key.public_point(), m_order),
m_kdf_hash(kdf_hash)
{}
size_t max_input_bits() const override
{
// This is arbitrary, but assumes SM2 is used for key encapsulation
return 512;
}
secure_vector<uint8_t> encrypt(const uint8_t msg[],
size_t msg_len,
RandomNumberGenerator& rng) override
{
std::unique_ptr<HashFunction> hash = HashFunction::create_or_throw(m_kdf_hash);
std::unique_ptr<KDF> kdf = KDF::create_or_throw("KDF2(" + m_kdf_hash + ")");
secure_vector<uint8_t> ciphertext;
ciphertext.reserve(1 + m_p_bytes*2 + msg_len + hash->output_length());
const BigInt k = BigInt::random_integer(rng, 1, m_order);
const PointGFp C1 = m_base_point.blinded_multiply(k, rng);
const BigInt x1 = C1.get_affine_x();
const BigInt y1 = C1.get_affine_y();
std::vector<uint8_t> x1_bytes(m_p_bytes);
std::vector<uint8_t> y1_bytes(m_p_bytes);
BigInt::encode_1363(x1_bytes.data(), x1_bytes.size(), x1);
BigInt::encode_1363(y1_bytes.data(), y1_bytes.size(), y1);
const PointGFp kPB = m_public_point.blinded_multiply(k, rng);
const BigInt x2 = kPB.get_affine_x();
const BigInt y2 = kPB.get_affine_y();
std::vector<uint8_t> x2_bytes(m_p_bytes);
std::vector<uint8_t> y2_bytes(m_p_bytes);
BigInt::encode_1363(x2_bytes.data(), x2_bytes.size(), x2);
BigInt::encode_1363(y2_bytes.data(), y2_bytes.size(), y2);
secure_vector<uint8_t> kdf_input;
kdf_input += x2_bytes;
kdf_input += y2_bytes;
const secure_vector<uint8_t> kdf_output =
kdf->derive_key(msg_len, kdf_input.data(), kdf_input.size());
secure_vector<uint8_t> masked_msg(msg_len);
xor_buf(masked_msg.data(), msg, kdf_output.data(), msg_len);
hash->update(x2_bytes);
hash->update(msg, msg_len);
hash->update(y2_bytes);
std::vector<uint8_t> C3(hash->output_length());
hash->final(C3.data());
ciphertext.push_back(0x04);
ciphertext += x1_bytes;
ciphertext += y1_bytes;
ciphertext += C3;
ciphertext += masked_msg;
return ciphertext;
}
private:
size_t m_p_bytes;
const BigInt& m_order;
Blinded_Point_Multiply m_base_point;
Blinded_Point_Multiply m_public_point;
const std::string m_kdf_hash;
};
class SM2_Decryption_Operation : public PK_Ops::Decryption
{
public:
SM2_Decryption_Operation(const SM2_Encryption_PrivateKey& key,
RandomNumberGenerator& rng,
const std::string& kdf_hash) :
m_key(key),
m_rng(rng),
m_kdf_hash(kdf_hash)
{}
secure_vector<uint8_t> decrypt(uint8_t& valid_mask,
const uint8_t ciphertext[],
size_t ciphertext_len) override
{
const BigInt& cofactor = m_key.domain().get_cofactor();
const size_t p_bytes = m_key.domain().get_curve().get_p().bytes();
valid_mask = 0;
std::unique_ptr<HashFunction> hash = HashFunction::create_or_throw(m_kdf_hash);
std::unique_ptr<KDF> kdf = KDF::create_or_throw("KDF2(" + m_kdf_hash + ")");
// Too short to be valid - no timing problem from early return
if(ciphertext_len < 1 + p_bytes*2 + hash->output_length())
{
return secure_vector<uint8_t>();
}
if(ciphertext[0] != 0x04)
{
return secure_vector<uint8_t>();
}
const size_t msg_len = ciphertext_len - (1 + p_bytes*2 + hash->output_length());
const PointGFp C1 = OS2ECP(ciphertext, 1 + p_bytes*2, m_key.domain().get_curve());
// OS2ECP verifies C1 is on the curve
Blinded_Point_Multiply C1_mul(C1, m_key.domain().get_order());
if(cofactor > 1 && C1_mul.blinded_multiply(cofactor, m_rng).is_zero())
{
return secure_vector<uint8_t>();
}
const PointGFp dbC1 = C1_mul.blinded_multiply(m_key.private_value(), m_rng);
const BigInt x2 = dbC1.get_affine_x();
const BigInt y2 = dbC1.get_affine_y();
std::vector<uint8_t> x2_bytes(p_bytes);
std::vector<uint8_t> y2_bytes(p_bytes);
BigInt::encode_1363(x2_bytes.data(), x2_bytes.size(), x2);
BigInt::encode_1363(y2_bytes.data(), y2_bytes.size(), y2);
secure_vector<uint8_t> kdf_input;
kdf_input += x2_bytes;
kdf_input += y2_bytes;
const secure_vector<uint8_t> kdf_output =
kdf->derive_key(msg_len, kdf_input.data(), kdf_input.size());
secure_vector<uint8_t> msg(msg_len);
xor_buf(msg.data(), ciphertext + (1+p_bytes*2+hash->output_length()), kdf_output.data(), msg_len);
hash->update(x2_bytes);
hash->update(msg);
hash->update(y2_bytes);
secure_vector<uint8_t> u = hash->final();
if(constant_time_compare(u.data(), ciphertext + (1+p_bytes*2), hash->output_length()) == false)
return secure_vector<uint8_t>();
valid_mask = 0xFF;
return msg;
}
private:
const SM2_Encryption_PrivateKey& m_key;
RandomNumberGenerator& m_rng;
const std::string m_kdf_hash;
};
}
std::unique_ptr<PK_Ops::Encryption>
SM2_Encryption_PublicKey::create_encryption_op(RandomNumberGenerator& /*rng*/,
const std::string& params,
const std::string& provider) const
{
if(provider == "base" || provider.empty())
{
const std::string kdf_hash = (params.empty() ? "SM3" : params);
return std::unique_ptr<PK_Ops::Encryption>(new SM2_Encryption_Operation(*this, kdf_hash));
}
throw Provider_Not_Found(algo_name(), provider);
}
std::unique_ptr<PK_Ops::Decryption>
SM2_Encryption_PrivateKey::create_decryption_op(RandomNumberGenerator& rng,
const std::string& params,
const std::string& provider) const
{
if(provider == "base" || provider.empty())
{
const std::string kdf_hash = (params.empty() ? "SM3" : params);
return std::unique_ptr<PK_Ops::Decryption>(new SM2_Decryption_Operation(*this, rng, kdf_hash));
}
throw Provider_Not_Found(algo_name(), provider);
}
}
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