/*
* Copyright (c) 2023, stelar7 <dudedbz@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/ByteReader.h>
#include <AK/Endian.h>
#include <LibCrypto/AEAD/ChaCha20Poly1305.h>
#include <LibCrypto/Authentication/Poly1305.h>
#include <LibCrypto/Cipher/ChaCha20.h>
namespace Crypto::AEAD {
// https://datatracker.ietf.org/doc/html/rfc8439#section-2.6
ErrorOr<ByteBuffer> ChaCha20Poly1305::poly1305_key()
{
Crypto::Cipher::ChaCha20 cipher(m_key, m_nonce, 0);
cipher.generate_block();
auto state = cipher.block();
return TRY(ByteBuffer::copy(state.slice(0, 32)));
}
// https://datatracker.ietf.org/doc/html/rfc8439#section-2.8
ErrorOr<ByteBuffer> ChaCha20Poly1305::encrypt(ReadonlyBytes aad, ReadonlyBytes input_plaintext)
{
// First, a Poly1305 one-time key is generated from the 256-bit key
// and nonce using the procedure described in Section 2.6.
auto otk = TRY(poly1305_key());
// Next, the ChaCha20 encryption function is called to encrypt the
// plaintext, using the same key and nonce, and with the initial
// counter set to 1.
auto ciphertext_buffer = TRY(ByteBuffer::create_zeroed(input_plaintext.size()));
auto ciphertext = ciphertext_buffer.bytes();
auto chacha = Crypto::Cipher::ChaCha20(m_key, m_nonce, 1);
chacha.encrypt(input_plaintext, ciphertext);
// Finally, the Poly1305 function is called with the Poly1305 key
// calculated above, and a message constructed as a concatenation of
// the following:
auto mac_data = TRY(ByteBuffer::create_zeroed(0));
auto buffer_size = aad.size() + pad_to_16(aad) + ciphertext_buffer.size() + pad_to_16(ciphertext_buffer) + sizeof(u64) + sizeof(u64);
mac_data.ensure_capacity(buffer_size);
// The AAD
mac_data.append(aad);
// padding1 -- the padding is up to 15 zero bytes, and it brings
// the total length so far to an integral multiple of 16. If the
// length of the AAD was already an integral multiple of 16 bytes,
// this field is zero-length.
for (size_t i = 0; i < pad_to_16(aad); ++i)
mac_data.append(0);
// The ciphertext
mac_data.append(ciphertext);
// padding2 -- the padding is up to 15 zero bytes, and it brings
// the total length so far to an integral multiple of 16. If the
// length of the ciphertext was already an integral multiple of 16
// bytes, this field is zero-length.
for (size_t i = 0; i < pad_to_16(ciphertext); ++i)
mac_data.append(0);
u8 placeholder[8] = { 0 };
// The length of the additional data in octets (as a 64-bit little-endian integer).
mac_data.append(ReadonlyBytes { placeholder, 8 });
ByteReader::store(static_cast<u8*>(mac_data.end_pointer()) - sizeof(u64), AK::convert_between_host_and_little_endian(static_cast<u64>(aad.size())));
// The length of the ciphertext in octets (as a 64-bit little-endian integer).
mac_data.append(ReadonlyBytes { placeholder, 8 });
ByteReader::store(static_cast<u8*>(mac_data.end_pointer()) - sizeof(u64), AK::convert_between_host_and_little_endian(static_cast<u64>(ciphertext.size())));
Crypto::Authentication::Poly1305 mac_function(otk);
mac_function.update(mac_data.bytes());
auto tag = TRY(mac_function.digest());
// The output from the AEAD is the concatenation of:
auto result = TRY(ByteBuffer::create_zeroed(0));
result.ensure_capacity(ciphertext.size() + tag.size());
// A ciphertext of the same length as the plaintext.
result.append(ciphertext);
// A 128-bit tag, which is the output of the Poly1305 function.
result.append(tag);
return result;
}
// https://datatracker.ietf.org/doc/html/rfc8439#section-2.8
ErrorOr<ByteBuffer> ChaCha20Poly1305::decrypt(ReadonlyBytes aad, ReadonlyBytes ciphertext)
{
// Decryption is similar with the following differences:
// o The roles of ciphertext and plaintext are reversed, so the
// ChaCha20 encryption function is applied to the ciphertext,
// producing the plaintext.
// o The Poly1305 function is still run on the AAD and the ciphertext,
// not the plaintext.
// First, a Poly1305 one-time key is generated from the 256-bit key
// and nonce using the procedure described in Section 2.6.
auto otk = TRY(poly1305_key());
// Next, the ChaCha20 encryption function is called to decrypt the
// ciphertext, using the same key and nonce, and with the initial
// counter set to 1.
auto chacha = Crypto::Cipher::ChaCha20(m_key, m_nonce, 1);
auto plaintext_buffer = TRY(ByteBuffer::create_zeroed(ciphertext.size()));
auto plaintext = plaintext_buffer.bytes();
chacha.encrypt(ciphertext, plaintext);
// Finally, the Poly1305 function is called with the Poly1305 key
// calculated above, and a message constructed as a concatenation of
// the following:
auto mac_data = TRY(ByteBuffer::create_zeroed(0));
auto buffer_size = aad.size() + pad_to_16(aad) + ciphertext.size() + pad_to_16(ciphertext) + sizeof(u64) + sizeof(u64);
mac_data.ensure_capacity(buffer_size);
// The AAD
mac_data.append(aad);
// padding1 -- the padding is up to 15 zero bytes, and it brings
// the total length so far to an integral multiple of 16. If the
// length of the AAD was already an integral multiple of 16 bytes,
// this field is zero-length.
for (size_t i = 0; i < pad_to_16(aad); ++i)
mac_data.append(0);
// The ciphertext
mac_data.append(ciphertext);
// padding2 -- the padding is up to 15 zero bytes, and it brings
// the total length so far to an integral multiple of 16. If the
// length of the ciphertext was already an integral multiple of 16
// bytes, this field is zero-length.
for (size_t i = 0; i < pad_to_16(ciphertext); ++i)
mac_data.append(0);
u8 placeholder[8] = { 0 };
// The length of the additional data in octets (as a 64-bit little-endian integer).
mac_data.append(ReadonlyBytes { placeholder, 8 });
ByteReader::store(static_cast<u8*>(mac_data.end_pointer()) - sizeof(u64), AK::convert_between_host_and_little_endian(static_cast<u64>(aad.size())));
// The length of the ciphertext in octets (as a 64-bit little-endian integer).
mac_data.append(ReadonlyBytes { placeholder, 8 });
ByteReader::store(static_cast<u8*>(mac_data.end_pointer()) - sizeof(u64), AK::convert_between_host_and_little_endian(static_cast<u64>(ciphertext.size())));
Crypto::Authentication::Poly1305 mac_function(otk);
mac_function.update(mac_data.bytes());
auto tag = TRY(mac_function.digest());
// The output from the AEAD is the concatenation of:
auto result = TRY(ByteBuffer::create_zeroed(0));
result.ensure_capacity(plaintext.size() + tag.size());
// A plaintext of the same length as the ciphertext.
result.append(plaintext);
// A 128-bit tag, which is the output of the Poly1305 function.
result.append(tag);
return result;
}
// https://datatracker.ietf.org/doc/html/rfc8439#section-4
bool ChaCha20Poly1305::verify_tag(ReadonlyBytes encrypted, ReadonlyBytes decrypted)
{
// With online protocols, implementation MUST use a constant-time comparison function rather
// than relying on optimized but insecure library functions such as the C language's memcmp().
auto encrypted_tag = encrypted.slice_from_end(16);
auto decrypted_tag = decrypted.slice_from_end(16);
if (encrypted_tag.size() != decrypted_tag.size())
return false;
auto result = 0;
for (size_t i = 0; i < encrypted_tag.size(); ++i)
result |= encrypted_tag[i] ^ decrypted_tag[i];
return result == 0;
}
}
