Method Initialize

src/bip324.cpp:34–71

    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(std::span<const std::byte> contents, std::span<const std::byte> aad, bool ignore, std::span<std::byte> output) noexcept
{