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/*
* Copyright (c) 2020, Ali Mohammad Pur <ali.mpfard@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Random.h>
#include <LibCrypto/PK/Code/Code.h>
static constexpr u8 zeros[] { 0, 0, 0, 0, 0, 0, 0, 0 };
namespace Crypto {
namespace PK {
template<typename HashFunction, size_t SaltSize>
class EMSA_PSS : public Code<HashFunction> {
public:
template<typename... Args>
EMSA_PSS(Args... args)
: Code<HashFunction>(args...)
{
m_buffer = Bytes { m_data_buffer, sizeof(m_data_buffer) };
}
static constexpr auto SaltLength = SaltSize;
virtual void encode(ReadonlyBytes in, ByteBuffer& out, size_t em_bits) override
{
// FIXME: we're supposed to check if in.size() > HashFunction::input_limitation
// however, all of our current hash functions can hash unlimited blocks
auto& hash_fn = this->hasher();
hash_fn.update(in);
auto message_hash = hash_fn.digest();
auto hash_length = hash_fn.DigestSize;
auto em_length = (em_bits + 7) / 8;
u8 salt[SaltLength];
fill_with_random(salt, SaltLength);
if (em_length < hash_length + SaltLength + 2) {
dbgln("Ooops...encoding error");
return;
}
m_buffer.overwrite(0, zeros, 8);
m_buffer.overwrite(8, message_hash.data, HashFunction::DigestSize);
m_buffer.overwrite(8 + HashFunction::DigestSize, salt, SaltLength);
hash_fn.update(m_buffer);
auto hash = hash_fn.digest();
u8 DB_data[em_length - HashFunction::DigestSize - 1];
auto DB = Bytes { DB_data, em_length - HashFunction::DigestSize - 1 };
auto DB_offset = 0;
for (size_t i = 0; i < em_length - SaltLength - HashFunction::DigestSize - 2; ++i)
DB[DB_offset++] = 0;
DB[DB_offset++] = 0x01;
DB.overwrite(DB_offset, salt, SaltLength);
auto mask_length = em_length - HashFunction::DigestSize - 1;
u8 DB_mask[mask_length];
auto DB_mask_buffer = Bytes { DB_mask, mask_length };
// FIXME: we should probably allow reading from u8*
MGF1(ReadonlyBytes { hash.data, HashFunction::DigestSize }, mask_length, DB_mask_buffer);
for (size_t i = 0; i < DB.size(); ++i)
DB_data[i] ^= DB_mask[i];
auto count = (8 - (em_length * 8 - em_bits));
DB_data[0] &= (0xff >> count) << count;
out.overwrite(0, DB.data(), DB.size());
out.overwrite(DB.size(), hash.data, hash_fn.DigestSize);
out[DB.size() + hash_fn.DigestSize] = 0xbc;
}
virtual VerificationConsistency verify(ReadonlyBytes msg, ReadonlyBytes emsg, size_t em_bits) override
{
auto& hash_fn = this->hasher();
hash_fn.update(msg);
auto message_hash = hash_fn.digest();
if (emsg.size() < HashFunction::DigestSize + SaltLength + 2)
return VerificationConsistency::Inconsistent;
if (emsg[emsg.size() - 1] != 0xbc)
return VerificationConsistency::Inconsistent;
auto mask_length = emsg.size() - HashFunction::DigestSize - 1;
auto masked_DB = emsg.slice(0, mask_length);
auto H = emsg.slice(mask_length, HashFunction::DigestSize);
auto length_to_check = 8 * emsg.size() - em_bits;
auto octet = masked_DB[0];
for (size_t i = 0; i < length_to_check; ++i)
if ((octet >> (8 - i)) & 0x01)
return VerificationConsistency::Inconsistent;
u8 DB_mask[mask_length];
auto DB_mask_buffer = Bytes { DB_mask, mask_length };
MGF1(H, mask_length, DB_mask_buffer);
u8 DB[mask_length];
for (size_t i = 0; i < mask_length; ++i)
DB[i] = masked_DB[i] ^ DB_mask[i];
DB[0] &= 0xff >> (8 - length_to_check);
auto check_octets = emsg.size() - HashFunction::DigestSize - SaltLength - 2;
for (size_t i = 0; i < check_octets; ++i) {
if (DB[i])
return VerificationConsistency::Inconsistent;
}
if (DB[check_octets + 1] != 0x01)
return VerificationConsistency::Inconsistent;
auto* salt = DB + mask_length - SaltLength;
u8 m_prime[8 + HashFunction::DigestSize + SaltLength] { 0, 0, 0, 0, 0, 0, 0, 0 };
auto m_prime_buffer = Bytes { m_prime, sizeof(m_prime) };
m_prime_buffer.overwrite(8, message_hash.data, HashFunction::DigestSize);
m_prime_buffer.overwrite(8 + HashFunction::DigestSize, salt, SaltLength);
hash_fn.update(m_prime_buffer);
auto H_prime = hash_fn.digest();
if (__builtin_memcmp(message_hash.data, H_prime.data, HashFunction::DigestSize))
return VerificationConsistency::Inconsistent;
return VerificationConsistency::Consistent;
}
void MGF1(ReadonlyBytes seed, size_t length, Bytes out)
{
auto& hash_fn = this->hasher();
ByteBuffer T = ByteBuffer::create_zeroed(0);
for (size_t counter = 0; counter < length / HashFunction::DigestSize - 1; ++counter) {
hash_fn.update(seed);
hash_fn.update((u8*)&counter, 4);
T.append(hash_fn.digest().data, HashFunction::DigestSize);
}
out.overwrite(0, T.data(), length);
}
private:
u8 m_data_buffer[8 + HashFunction::DigestSize + SaltLength];
Bytes m_buffer;
};
}
}
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