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// Copyright (c) 2017-2022 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_CRYPTO_CHACHA20_H
#define BITCOIN_CRYPTO_CHACHA20_H
#include <span.h>
#include <array>
#include <cstddef>
#include <cstdlib>
#include <stdint.h>
#include <utility>
// classes for ChaCha20 256-bit stream cipher developed by Daniel J. Bernstein
// https://cr.yp.to/chacha/chacha-20080128.pdf.
//
// The 128-bit input is here implemented as a 96-bit nonce and a 32-bit block
// counter, as in RFC8439 Section 2.3. When the 32-bit block counter overflows
// the first 32-bit part of the nonce is automatically incremented, making it
// conceptually compatible with variants that use a 64/64 split instead.
/** ChaCha20 cipher that only operates on multiples of 64 bytes. */
class ChaCha20Aligned
{
private:
uint32_t input[12];
public:
/** Expected key length in constructor and SetKey. */
static constexpr unsigned KEYLEN{32};
/** Block size (inputs/outputs to Keystream / Crypt should be multiples of this). */
static constexpr unsigned BLOCKLEN{64};
/** For safety, disallow initialization without key. */
ChaCha20Aligned() noexcept = delete;
/** Initialize a cipher with specified 32-byte key. */
ChaCha20Aligned(Span<const std::byte> key) noexcept;
/** Destructor to clean up private memory. */
~ChaCha20Aligned();
/** Set 32-byte key, and seek to nonce 0 and block position 0. */
void SetKey(Span<const std::byte> key) noexcept;
/** Type for 96-bit nonces used by the Set function below.
*
* The first field corresponds to the LE32-encoded first 4 bytes of the nonce, also referred
* to as the '32-bit fixed-common part' in Example 2.8.2 of RFC8439.
*
* The second field corresponds to the LE64-encoded last 8 bytes of the nonce.
*
*/
using Nonce96 = std::pair<uint32_t, uint64_t>;
/** Set the 96-bit nonce and 32-bit block counter.
*
* Block_counter selects a position to seek to (to byte BLOCKLEN*block_counter). After 256 GiB,
* the block counter overflows, and nonce.first is incremented.
*/
void Seek(Nonce96 nonce, uint32_t block_counter) noexcept;
/** outputs the keystream into out, whose length must be a multiple of BLOCKLEN. */
void Keystream(Span<std::byte> out) noexcept;
/** en/deciphers the message <input> and write the result into <output>
*
* The size of input and output must be equal, and be a multiple of BLOCKLEN.
*/
void Crypt(Span<const std::byte> input, Span<std::byte> output) noexcept;
};
/** Unrestricted ChaCha20 cipher. */
class ChaCha20
{
private:
ChaCha20Aligned m_aligned;
std::array<std::byte, ChaCha20Aligned::BLOCKLEN> m_buffer;
unsigned m_bufleft{0};
public:
/** Expected key length in constructor and SetKey. */
static constexpr unsigned KEYLEN = ChaCha20Aligned::KEYLEN;
/** For safety, disallow initialization without key. */
ChaCha20() noexcept = delete;
/** Initialize a cipher with specified 32-byte key. */
ChaCha20(Span<const std::byte> key) noexcept : m_aligned(key) {}
/** Destructor to clean up private memory. */
~ChaCha20();
/** Set 32-byte key, and seek to nonce 0 and block position 0. */
void SetKey(Span<const std::byte> key) noexcept;
/** 96-bit nonce type. */
using Nonce96 = ChaCha20Aligned::Nonce96;
/** Set the 96-bit nonce and 32-bit block counter. See ChaCha20Aligned::Seek. */
void Seek(Nonce96 nonce, uint32_t block_counter) noexcept
{
m_aligned.Seek(nonce, block_counter);
m_bufleft = 0;
}
/** en/deciphers the message <in_bytes> and write the result into <out_bytes>
*
* The size of in_bytes and out_bytes must be equal.
*/
void Crypt(Span<const std::byte> in_bytes, Span<std::byte> out_bytes) noexcept;
/** outputs the keystream to out. */
void Keystream(Span<std::byte> out) noexcept;
};
/** Forward-secure ChaCha20
*
* This implements a stream cipher that automatically transitions to a new stream with a new key
* and new nonce after a predefined number of encryptions or decryptions.
*
* See BIP324 for details.
*/
class FSChaCha20
{
private:
/** Internal stream cipher. */
ChaCha20 m_chacha20;
/** The number of encryptions/decryptions before a rekey happens. */
const uint32_t m_rekey_interval;
/** The number of encryptions/decryptions since the last rekey. */
uint32_t m_chunk_counter{0};
/** The number of rekey operations that have happened. */
uint64_t m_rekey_counter{0};
public:
/** Length of keys expected by the constructor. */
static constexpr unsigned KEYLEN = 32;
// No copy or move to protect the secret.
FSChaCha20(const FSChaCha20&) = delete;
FSChaCha20(FSChaCha20&&) = delete;
FSChaCha20& operator=(const FSChaCha20&) = delete;
FSChaCha20& operator=(FSChaCha20&&) = delete;
/** Construct an FSChaCha20 cipher that rekeys every rekey_interval Crypt() calls. */
FSChaCha20(Span<const std::byte> key, uint32_t rekey_interval) noexcept;
/** Encrypt or decrypt a chunk. */
void Crypt(Span<const std::byte> input, Span<std::byte> output) noexcept;
};
#endif // BITCOIN_CRYPTO_CHACHA20_H
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