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/*
* SM2 Encryption
* (C) 2017 Ribose Inc
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/sm2.h>
#include <botan/internal/point_mul.h>
#include <botan/pk_ops.h>
#include <botan/der_enc.h>
#include <botan/ber_dec.h>
#include <botan/kdf.h>
#include <botan/hash.h>
namespace Botan {
namespace {
class SM2_Encryption_Operation final : public PK_Ops::Encryption
{
public:
SM2_Encryption_Operation(const SM2_Encryption_PublicKey& key,
RandomNumberGenerator& rng,
const std::string& kdf_hash) :
m_group(key.domain()),
m_kdf_hash(kdf_hash),
m_ws(PointGFp::WORKSPACE_SIZE),
m_mul_public_point(key.public_point(), rng, m_ws)
{
std::unique_ptr<HashFunction> hash = HashFunction::create_or_throw(m_kdf_hash);
m_hash_size = hash->output_length();
}
size_t max_input_bits() const override
{
// This is arbitrary, but assumes SM2 is used for key encapsulation
return 512;
}
size_t ciphertext_length(size_t ptext_len) const override
{
const size_t elem_size = m_group.get_order_bytes();
const size_t der_overhead = 16;
return der_overhead + 2*elem_size + m_hash_size + ptext_len;
}
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 + ")");
const size_t p_bytes = m_group.get_p_bytes();
const BigInt k = m_group.random_scalar(rng);
const PointGFp C1 = m_group.blinded_base_point_multiply(k, rng, m_ws);
const BigInt x1 = C1.get_affine_x();
const BigInt y1 = C1.get_affine_y();
std::vector<uint8_t> x1_bytes(p_bytes);
std::vector<uint8_t> y1_bytes(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_mul_public_point.mul(k, rng, m_group.get_order(), m_ws);
const BigInt x2 = kPB.get_affine_x();
const BigInt y2 = kPB.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> 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());
return DER_Encoder()
.start_cons(SEQUENCE)
.encode(x1)
.encode(y1)
.encode(C3, OCTET_STRING)
.encode(masked_msg, OCTET_STRING)
.end_cons()
.get_contents();
}
private:
const EC_Group m_group;
const std::string m_kdf_hash;
std::vector<BigInt> m_ws;
PointGFp_Var_Point_Precompute m_mul_public_point;
size_t m_hash_size;
};
class SM2_Decryption_Operation final : 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)
{
std::unique_ptr<HashFunction> hash = HashFunction::create_or_throw(m_kdf_hash);
m_hash_size = hash->output_length();
}
size_t plaintext_length(size_t ptext_len) const override
{
/*
* This ignores the DER encoding and so overestimates the
* plaintext length by 12 bytes or so
*/
const size_t elem_size = m_key.domain().get_order_bytes();
if(ptext_len < 2*elem_size + m_hash_size)
return 0;
return ptext_len - (2*elem_size + m_hash_size);
}
secure_vector<uint8_t> decrypt(uint8_t& valid_mask,
const uint8_t ciphertext[],
size_t ciphertext_len) override
{
const EC_Group& group = m_key.domain();
const BigInt& cofactor = group.get_cofactor();
const size_t p_bytes = group.get_p_bytes();
valid_mask = 0x00;
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>();
}
BigInt x1, y1;
secure_vector<uint8_t> C3, masked_msg;
BER_Decoder(ciphertext, ciphertext_len)
.start_cons(SEQUENCE)
.decode(x1)
.decode(y1)
.decode(C3, OCTET_STRING)
.decode(masked_msg, OCTET_STRING)
.end_cons()
.verify_end();
std::vector<uint8_t> recode_ctext;
DER_Encoder(recode_ctext)
.start_cons(SEQUENCE)
.encode(x1)
.encode(y1)
.encode(C3, OCTET_STRING)
.encode(masked_msg, OCTET_STRING)
.end_cons();
if(recode_ctext.size() != ciphertext_len)
return secure_vector<uint8_t>();
if(same_mem(recode_ctext.data(), ciphertext, ciphertext_len) == false)
return secure_vector<uint8_t>();
PointGFp C1 = group.point(x1, y1);
C1.randomize_repr(m_rng);
// Here C1 is publically invalid, so no problem with early return:
if(!C1.on_the_curve())
return secure_vector<uint8_t>();
if(cofactor > 1 && (C1 * cofactor).is_zero())
{
return secure_vector<uint8_t>();
}
const PointGFp dbC1 = group.blinded_var_point_multiply(
C1, m_key.private_value(), m_rng, m_ws);
const BigInt x2 = dbC1.get_affine_x();
const BigInt y2 = dbC1.get_affine_y();
secure_vector<uint8_t> x2_bytes(p_bytes);
secure_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(masked_msg.size(), kdf_input.data(), kdf_input.size());
xor_buf(masked_msg.data(), kdf_output.data(), kdf_output.size());
hash->update(x2_bytes);
hash->update(masked_msg);
hash->update(y2_bytes);
secure_vector<uint8_t> u = hash->final();
if(constant_time_compare(u.data(), C3.data(), hash->output_length()) == false)
return secure_vector<uint8_t>();
valid_mask = 0xFF;
return masked_msg;
}
private:
const SM2_Encryption_PrivateKey& m_key;
RandomNumberGenerator& m_rng;
const std::string m_kdf_hash;
std::vector<BigInt> m_ws;
size_t m_hash_size;
};
}
std::unique_ptr<PK_Ops::Encryption>
SM2_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, rng, kdf_hash));
}
throw Provider_Not_Found(algo_name(), provider);
}
std::unique_ptr<PK_Ops::Decryption>
SM2_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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