// 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; }