Line data    Source code

       1             : // Copyright (c) 2023 The Bitcoin Core developers
       2             : // Distributed under the MIT software license, see the accompanying
       3             : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
       4             : 
       5             : #include <bip324.h>
       6             : 
       7             : #include <chainparams.h>
       8             : #include <crypto/chacha20.h>
       9             : #include <crypto/chacha20poly1305.h>
      10             : #include <crypto/hkdf_sha256_32.h>
      11             : #include <key.h>
      12             : #include <pubkey.h>
      13             : #include <random.h>
      14             : #include <span.h>
      15             : #include <support/cleanse.h>
      16             : #include <uint256.h>
      17             : 
      18             : #include <algorithm>
      19             : #include <assert.h>
      20             : #include <cstdint>
      21             : #include <cstddef>
      22             : #include <iterator>
      23             : #include <string>
      24             : 
      25           0 : BIP324Cipher::BIP324Cipher(const CKey& key, Span<const std::byte> ent32) noexcept :
      26           0 :     m_key(key)
      27             : {
      28           0 :     m_our_pubkey = m_key.EllSwiftCreate(ent32);
      29           0 : }
      30             : 
      31           0 : BIP324Cipher::BIP324Cipher(const CKey& key, const EllSwiftPubKey& pubkey) noexcept :
      32           0 :     m_key(key), m_our_pubkey(pubkey) {}
      33             : 
      34           0 : void BIP324Cipher::Initialize(const EllSwiftPubKey& their_pubkey, bool initiator, bool self_decrypt) noexcept
      35             : {
      36             :     // Determine salt (fixed string + network magic bytes)
      37           0 :     const auto& message_header = Params().MessageStart();
      38           0 :     std::string salt = std::string{"bitcoin_v2_shared_secret"} + std::string(std::begin(message_header), std::end(message_header));
      39             : 
      40             :     // Perform ECDH to derive shared secret.
      41           0 :     ECDHSecret ecdh_secret = m_key.ComputeBIP324ECDHSecret(their_pubkey, m_our_pubkey, initiator);
      42             : 
      43             :     // Derive encryption keys from shared secret, and initialize stream ciphers and AEADs.
      44           0 :     bool side = (initiator != self_decrypt);
      45           0 :     CHKDF_HMAC_SHA256_L32 hkdf(UCharCast(ecdh_secret.data()), ecdh_secret.size(), salt);
      46             :     std::array<std::byte, 32> hkdf_32_okm;
      47           0 :     hkdf.Expand32("initiator_L", UCharCast(hkdf_32_okm.data()));
      48           0 :     (side ? m_send_l_cipher : m_recv_l_cipher).emplace(hkdf_32_okm, REKEY_INTERVAL);
      49           0 :     hkdf.Expand32("initiator_P", UCharCast(hkdf_32_okm.data()));
      50           0 :     (side ? m_send_p_cipher : m_recv_p_cipher).emplace(hkdf_32_okm, REKEY_INTERVAL);
      51           0 :     hkdf.Expand32("responder_L", UCharCast(hkdf_32_okm.data()));
      52           0 :     (side ? m_recv_l_cipher : m_send_l_cipher).emplace(hkdf_32_okm, REKEY_INTERVAL);
      53           0 :     hkdf.Expand32("responder_P", UCharCast(hkdf_32_okm.data()));
      54           0 :     (side ? m_recv_p_cipher : m_send_p_cipher).emplace(hkdf_32_okm, REKEY_INTERVAL);
      55             : 
      56             :     // Derive garbage terminators from shared secret.
      57           0 :     hkdf.Expand32("garbage_terminators", UCharCast(hkdf_32_okm.data()));
      58           0 :     std::copy(std::begin(hkdf_32_okm), std::begin(hkdf_32_okm) + GARBAGE_TERMINATOR_LEN,
      59           0 :         (initiator ? m_send_garbage_terminator : m_recv_garbage_terminator).begin());
      60           0 :     std::copy(std::end(hkdf_32_okm) - GARBAGE_TERMINATOR_LEN, std::end(hkdf_32_okm),
      61           0 :         (initiator ? m_recv_garbage_terminator : m_send_garbage_terminator).begin());
      62             : 
      63             :     // Derive session id from shared secret.
      64           0 :     hkdf.Expand32("session_id", UCharCast(m_session_id.data()));
      65             : 
      66             :     // Wipe all variables that contain information which could be used to re-derive encryption keys.
      67           0 :     memory_cleanse(ecdh_secret.data(), ecdh_secret.size());
      68           0 :     memory_cleanse(hkdf_32_okm.data(), sizeof(hkdf_32_okm));
      69           0 :     memory_cleanse(&hkdf, sizeof(hkdf));
      70           0 :     m_key = CKey();
      71           0 : }
      72             : 
      73           0 : void BIP324Cipher::Encrypt(Span<const std::byte> contents, Span<const std::byte> aad, bool ignore, Span<std::byte> output) noexcept
      74             : {
      75           0 :     assert(output.size() == contents.size() + EXPANSION);
      76             : 
      77             :     // Encrypt length.
      78             :     std::byte len[LENGTH_LEN];
      79           0 :     len[0] = std::byte{(uint8_t)(contents.size() & 0xFF)};
      80           0 :     len[1] = std::byte{(uint8_t)((contents.size() >> 8) & 0xFF)};
      81           0 :     len[2] = std::byte{(uint8_t)((contents.size() >> 16) & 0xFF)};
      82           0 :     m_send_l_cipher->Crypt(len, output.first(LENGTH_LEN));
      83             : 
      84             :     // Encrypt plaintext.
      85           0 :     std::byte header[HEADER_LEN] = {ignore ? IGNORE_BIT : std::byte{0}};
      86           0 :     m_send_p_cipher->Encrypt(header, contents, aad, output.subspan(LENGTH_LEN));
      87           0 : }
      88             : 
      89           0 : uint32_t BIP324Cipher::DecryptLength(Span<const std::byte> input) noexcept
      90             : {
      91           0 :     assert(input.size() == LENGTH_LEN);
      92             : 
      93             :     std::byte buf[LENGTH_LEN];
      94             :     // Decrypt length
      95           0 :     m_recv_l_cipher->Crypt(input, buf);
      96             :     // Convert to number.
      97           0 :     return uint32_t(buf[0]) + (uint32_t(buf[1]) << 8) + (uint32_t(buf[2]) << 16);
      98             : }
      99             : 
     100           0 : bool BIP324Cipher::Decrypt(Span<const std::byte> input, Span<const std::byte> aad, bool& ignore, Span<std::byte> contents) noexcept
     101             : {
     102           0 :     assert(input.size() + LENGTH_LEN == contents.size() + EXPANSION);
     103             : 
     104             :     std::byte header[HEADER_LEN];
     105           0 :     if (!m_recv_p_cipher->Decrypt(input, aad, header, contents)) return false;
     106             : 
     107           0 :     ignore = (header[0] & IGNORE_BIT) == IGNORE_BIT;
     108           0 :     return true;
     109           0 : }