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// Copyright (c) 2023 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_BIP324_H
#define BITCOIN_BIP324_H
#include <cstddef>
#include <optional>
#include <crypto/chacha20.h>
#include <crypto/chacha20poly1305.h>
#include <key.h>
#include <pubkey.h>
#include <span.h>
/** The BIP324 packet cipher, encapsulating its key derivation, stream cipher, and AEAD. */
class BIP324Cipher
{
public:
static constexpr unsigned SESSION_ID_LEN{32};
static constexpr unsigned GARBAGE_TERMINATOR_LEN{16};
static constexpr unsigned REKEY_INTERVAL{224};
static constexpr unsigned LENGTH_LEN{3};
static constexpr unsigned HEADER_LEN{1};
static constexpr unsigned EXPANSION = LENGTH_LEN + HEADER_LEN + FSChaCha20Poly1305::EXPANSION;
static constexpr std::byte IGNORE_BIT{0x80};
private:
std::optional<FSChaCha20> m_send_l_cipher;
std::optional<FSChaCha20> m_recv_l_cipher;
std::optional<FSChaCha20Poly1305> m_send_p_cipher;
std::optional<FSChaCha20Poly1305> m_recv_p_cipher;
CKey m_key;
EllSwiftPubKey m_our_pubkey;
std::array<std::byte, SESSION_ID_LEN> m_session_id;
std::array<std::byte, GARBAGE_TERMINATOR_LEN> m_send_garbage_terminator;
std::array<std::byte, GARBAGE_TERMINATOR_LEN> m_recv_garbage_terminator;
public:
/** Initialize a BIP324 cipher with securely generated random keys. */
BIP324Cipher() noexcept;
/** Initialize a BIP324 cipher with specified key and encoding entropy (testing only). */
BIP324Cipher(const CKey& key, Span<const std::byte> ent32) noexcept;
/** Initialize a BIP324 cipher with specified key (testing only). */
BIP324Cipher(const CKey& key, const EllSwiftPubKey& pubkey) noexcept;
/** Retrieve our public key. */
const EllSwiftPubKey& GetOurPubKey() const noexcept { return m_our_pubkey; }
/** Initialize when the other side's public key is received. Can only be called once. */
void Initialize(const EllSwiftPubKey& their_pubkey, bool initiator) noexcept;
/** Determine whether this cipher is fully initialized. */
explicit operator bool() const noexcept { return m_send_l_cipher.has_value(); }
/** Encrypt a packet. Only after Initialize().
*
* It must hold that output.size() == contents.size() + EXPANSION.
*/
void Encrypt(Span<const std::byte> contents, Span<const std::byte> aad, bool ignore, Span<std::byte> output) noexcept;
/** Decrypt the length of a packet. Only after Initialize().
*
* It must hold that input.size() == LENGTH_LEN.
*/
unsigned DecryptLength(Span<const std::byte> input) noexcept;
/** Decrypt a packet. Only after Initialize().
*
* It must hold that input.size() + LENGTH_LEN == contents.size() + EXPANSION.
* Contents.size() must equal the length returned by DecryptLength.
*/
bool Decrypt(Span<const std::byte> input, Span<const std::byte> aad, bool& ignore, Span<std::byte> contents) noexcept;
/** Get the Session ID. Only after Initialize(). */
Span<const std::byte> GetSessionID() const noexcept { return m_session_id; }
/** Get the Garbage Terminator to send. Only after Initialize(). */
Span<const std::byte> GetSendGarbageTerminator() const noexcept { return m_send_garbage_terminator; }
/** Get the expected Garbage Terminator to receive. Only after Initialize(). */
Span<const std::byte> GetReceiveGarbageTerminator() const noexcept { return m_recv_garbage_terminator; }
};
#endif // BITCOIN_BIP324_H
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