// 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.

#include <bip324.h>

#include <chainparams.h>

#include <crypto/chacha20.h>

#include <crypto/chacha20poly1305.h>

#include <crypto/hkdf_sha256_32.h>

#include <key.h>

#include <pubkey.h>

#include <random.h>

#include <span.h>

#include <support/cleanse.h>

#include <uint256.h>

#include <algorithm>

#include <assert.h>

#include <cstdint>

#include <cstddef>

#include <iterator>

#include <string>

BIP324Cipher::BIP324Cipher(const CKey& key, Span<const std::byte> ent32) noexcept :

    m_key(key)

{

    m_our_pubkey = m_key.EllSwiftCreate(ent32);

}

BIP324Cipher::BIP324Cipher(const CKey& key, const EllSwiftPubKey& pubkey) noexcept :

    m_key(key), m_our_pubkey(pubkey) {}

void BIP324Cipher::Initialize(const EllSwiftPubKey& their_pubkey, bool initiator, bool self_decrypt) noexcept

{

    // Determine salt (fixed string + network magic bytes)

    const auto& message_header = Params().MessageStart();

    std::string salt = std::string{"bitcoin_v2_shared_secret"} + std::string(std::begin(message_header), std::end(message_header));

    // Perform ECDH to derive shared secret.

    ECDHSecret ecdh_secret = m_key.ComputeBIP324ECDHSecret(their_pubkey, m_our_pubkey, initiator);

    // Derive encryption keys from shared secret, and initialize stream ciphers and AEADs.

    bool side = (initiator != self_decrypt);

    CHKDF_HMAC_SHA256_L32 hkdf(UCharCast(ecdh_secret.data()), ecdh_secret.size(), salt);

    std::array<std::byte, 32> hkdf_32_okm;

    hkdf.Expand32("initiator_L", UCharCast(hkdf_32_okm.data()));

    (side ? m_send_l_cipher : m_recv_l_cipher).emplace(hkdf_32_okm, REKEY_INTERVAL);

    hkdf.Expand32("initiator_P", UCharCast(hkdf_32_okm.data()));

    (side ? m_send_p_cipher : m_recv_p_cipher).emplace(hkdf_32_okm, REKEY_INTERVAL);

    hkdf.Expand32("responder_L", UCharCast(hkdf_32_okm.data()));

    (side ? m_recv_l_cipher : m_send_l_cipher).emplace(hkdf_32_okm, REKEY_INTERVAL);

    hkdf.Expand32("responder_P", UCharCast(hkdf_32_okm.data()));

    (side ? m_recv_p_cipher : m_send_p_cipher).emplace(hkdf_32_okm, REKEY_INTERVAL);

    // Derive garbage terminators from shared secret.

    hkdf.Expand32("garbage_terminators", UCharCast(hkdf_32_okm.data()));

    std::copy(std::begin(hkdf_32_okm), std::begin(hkdf_32_okm) + GARBAGE_TERMINATOR_LEN,

        (initiator ? m_send_garbage_terminator : m_recv_garbage_terminator).begin());

    std::copy(std::end(hkdf_32_okm) - GARBAGE_TERMINATOR_LEN, std::end(hkdf_32_okm),

        (initiator ? m_recv_garbage_terminator : m_send_garbage_terminator).begin());

    // Derive session id from shared secret.

    hkdf.Expand32("session_id", UCharCast(m_session_id.data()));

    // Wipe all variables that contain information which could be used to re-derive encryption keys.

    memory_cleanse(ecdh_secret.data(), ecdh_secret.size());

    memory_cleanse(hkdf_32_okm.data(), sizeof(hkdf_32_okm));

    memory_cleanse(&hkdf, sizeof(hkdf));

    m_key = CKey();

}

void BIP324Cipher::Encrypt(Span<const std::byte> contents, Span<const std::byte> aad, bool ignore, Span<std::byte> output) noexcept

{

    assert(output.size() == contents.size() + EXPANSION);

    // Encrypt length.

    std::byte len[LENGTH_LEN];

    len[0] = std::byte{(uint8_t)(contents.size() & 0xFF)};

    len[1] = std::byte{(uint8_t)((contents.size() >> 8) & 0xFF)};

    len[2] = std::byte{(uint8_t)((contents.size() >> 16) & 0xFF)};

    m_send_l_cipher->Crypt(len, output.first(LENGTH_LEN));

    // Encrypt plaintext.

    std::byte header[HEADER_LEN] = {ignore ? IGNORE_BIT : std::byte{0}};

    m_send_p_cipher->Encrypt(header, contents, aad, output.subspan(LENGTH_LEN));

}

uint32_t BIP324Cipher::DecryptLength(Span<const std::byte> input) noexcept

{

    assert(input.size() == LENGTH_LEN);

    std::byte buf[LENGTH_LEN];

    // Decrypt length

    m_recv_l_cipher->Crypt(input, buf);

    // Convert to number.

    return uint32_t(buf[0]) + (uint32_t(buf[1]) << 8) + (uint32_t(buf[2]) << 16);

}

bool BIP324Cipher::Decrypt(Span<const std::byte> input, Span<const std::byte> aad, bool& ignore, Span<std::byte> contents) noexcept

{

    assert(input.size() + LENGTH_LEN == contents.size() + EXPANSION);

    std::byte header[HEADER_LEN];

    if (!m_recv_p_cipher->Decrypt(input, aad, header, contents)) return false;

    ignore = (header[0] & IGNORE_BIT) == IGNORE_BIT;

    return true;

}