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/*
* Copyright (c) 2020, Ali Mohammad Pur <mpfard@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/OwnPtr.h>
#include <AK/String.h>
#include <AK/StringBuilder.h>
#include <AK/StringView.h>
#include <LibCrypto/Authentication/GHash.h>
#include <LibCrypto/Cipher/Mode/CTR.h>
#include <LibCrypto/Verification.h>
namespace Crypto {
namespace Cipher {
using IncrementFunction = IncrementInplace;
template<typename T>
class GCM : public CTR<T, IncrementFunction> {
public:
constexpr static size_t IVSizeInBits = 128;
virtual ~GCM() { }
template<typename... Args>
explicit constexpr GCM<T>(Args... args)
: CTR<T>(args...)
{
static_assert(T::BlockSizeInBits == 128u, "GCM Mode is only available for 128-bit Ciphers");
__builtin_memset(m_auth_key_storage, 0, block_size);
typename T::BlockType key_block(m_auth_key_storage, block_size);
this->cipher().encrypt_block(key_block, key_block);
key_block.bytes().copy_to(m_auth_key);
m_ghash = Authentication::GHash(m_auth_key);
}
virtual String class_name() const override
{
StringBuilder builder;
builder.append(this->cipher().class_name());
builder.append("_GCM");
return builder.build();
}
virtual size_t IV_length() const override { return IVSizeInBits / 8; }
// FIXME: This overload throws away the auth stuff, think up a better way to return more than a single bytebuffer.
virtual void encrypt(ReadonlyBytes in, Bytes& out, ReadonlyBytes ivec = {}, Bytes* = nullptr) override
{
VERIFY(!ivec.is_empty());
static ByteBuffer dummy;
encrypt(in, out, ivec, dummy, dummy);
}
virtual void decrypt(ReadonlyBytes in, Bytes& out, ReadonlyBytes ivec = {}) override
{
encrypt(in, out, ivec);
}
void encrypt(const ReadonlyBytes& in, Bytes out, const ReadonlyBytes& iv_in, const ReadonlyBytes& aad, Bytes tag)
{
auto iv_buf = ByteBuffer::copy(iv_in.data(), iv_in.size());
auto iv = iv_buf.bytes();
// Increment the IV for block 0
CTR<T>::increment(iv);
typename T::BlockType block0;
block0.overwrite(iv);
this->cipher().encrypt_block(block0, block0);
// Skip past block 0
CTR<T>::increment(iv);
if (in.is_empty())
CTR<T>::key_stream(out, iv);
else
CTR<T>::encrypt(in, out, iv);
auto auth_tag = m_ghash->process(aad, out);
block0.apply_initialization_vector({ auth_tag.data, array_size(auth_tag.data) });
block0.bytes().copy_to(tag);
}
VerificationConsistency decrypt(ReadonlyBytes in, Bytes out, ReadonlyBytes iv_in, ReadonlyBytes aad, ReadonlyBytes tag)
{
auto iv_buf = ByteBuffer::copy(iv_in.data(), iv_in.size());
auto iv = iv_buf.bytes();
// Increment the IV for block 0
CTR<T>::increment(iv);
typename T::BlockType block0;
block0.overwrite(iv);
this->cipher().encrypt_block(block0, block0);
// Skip past block 0
CTR<T>::increment(iv);
auto auth_tag = m_ghash->process(aad, in);
block0.apply_initialization_vector({ auth_tag.data, array_size(auth_tag.data) });
auto test_consistency = [&] {
if (block0.block_size() != tag.size() || __builtin_memcmp(block0.bytes().data(), tag.data(), tag.size()) != 0)
return VerificationConsistency::Inconsistent;
return VerificationConsistency::Consistent;
};
// FIXME: This block needs constant-time comparisons.
if (in.is_empty()) {
out = {};
return test_consistency();
}
CTR<T>::encrypt(in, out, iv);
return test_consistency();
}
private:
static constexpr auto block_size = T::BlockType::BlockSizeInBits / 8;
u8 m_auth_key_storage[block_size];
Bytes m_auth_key { m_auth_key_storage, block_size };
Optional<Authentication::GHash> m_ghash;
};
}
}
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