Repository: bitcoin/bitcoin
File: src/validation.cpp (C++)

Code before:
        // Consider the block mutated if any transaction is 64 bytes in size (see 3.1
        // in "Weaknesses in Bitcoin’s Merkle Root Construction":
        // https://lists.linuxfoundation.org/pipermail/bitcoin-dev/attachments/20190225/a27d8837/attachment-0001.pdf).
        //
        // Note: This is not a consensus change as this only applies to blocks that
        // don't have a coinbase transaction and would therefore already be invalid.
        return std::any_of(block.vtx.begin(), block.vtx.end(),
                           [](auto& tx) { return GetSerializeSize(TX_NO_WITNESS(tx)) == 64; });
    } else {
        // Theoretically it is still possible for a block with a 64 byte
        // coinbase transaction to be mutated but we neglect that possibility
        // here as it requires at least 224 bits of work.
    }

    if (!CheckWitnessMalleation(block, check_witness_root, state)) {
        LogDebug(BCLog::VALIDATION, "Block mutated: %s\n", state.ToString());
        return true;
    }

    return false;
}

arith_uint256 CalculateClaimedHeadersWork(std::span<const CBlockHeader> headers)
{
    arith_uint256 total_work{0};
    for (const CBlockHeader& header : headers) total_work += GetBlockProof(header);
    return total_work;
}

/** Context-dependent validity checks.
 *  By "context", we mean only the previous block headers, but not the UTXO
 *  set; UTXO-related validity checks are done in ConnectBlock().
 *  NOTE: This function is not currently invoked by ConnectBlock(), so we
 *  should consider upgrade issues if we change which consensus rules are
 *  enforced in this function (eg by adding a new consensus rule). See comment
 *  in ConnectBlock().
 *  Note that -reindex-chainstate skips the validation that happens here!
 *
 *  NOTE: failing to check the header's height against the last checkpoint's opened a DoS vector between
 *  v0.12 and v0.15 (when no additional protection was in place) whereby an attacker could unboundedly
 *  grow our in-memory block index. See https://bitcoincore.org/en/2024/07/03/disclose-header-spam.
 */
static bool ContextualCheckBlockHeader(const CBlockHeader& block, BlockValidationState& state, BlockManager& blockman, const ChainstateManager& chainman, const CBlockIndex* pindexPrev) EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
{
    AssertLockHeld(::cs_main);
    assert(pindexPrev != nullptr);
    const int nHeight = pindexPrev->nHeight + 1;

    // Check proof of work
    const Consensus::Params& consensusParams = chainman.GetConsensus();
    if (block.nBits != GetNextWorkRequired(pindexPrev, &block, consensusParams))

Review comment (suggestion):
nit in 2dcf2e4a854c21b71dc133e2fd891b0757204f43:
IMO should keep braces as they already existed on master and only `if` are allowed to omit braces according to *developer-notes.md*.
```suggestion
    for (const CBlockHeader& header : headers) {
        total_work += GetBlockProof(header);
    }
```

Code after:
}

/** Context-dependent validity checks.
 *  By "context", we mean only the previous block headers, but not the UTXO
 *  set; UTXO-related validity checks are done in ConnectBlock().
 *  NOTE: This function is not currently invoked by ConnectBlock(), so we
 *  should consider upgrade issues if we change which consensus rules are
 *  enforced in this function (eg by adding a new consensus rule). See comment
 *  in ConnectBlock().
 *  Note that -reindex-chainstate skips the validation that happens here!
 *
 *  NOTE: failing to check the header's height against the last checkpoint's opened a DoS vector between
 *  v0.12 and v0.15 (when no additional protection was in place) whereby an attacker could unboundedly
 *  grow our in-memory block index. See https://bitcoincore.org/en/2024/07/03/disclose-header-spam.
 */
static bool ContextualCheckBlockHeader(const CBlockHeader& block, BlockValidationState& state, BlockManager& blockman, const ChainstateManager& chainman, const CBlockIndex* pindexPrev) EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
{
    AssertLockHeld(::cs_main);
    assert(pindexPrev != nullptr);
    const int nHeight = pindexPrev->nHeight + 1;

    // Check proof of work
    const Consensus::Params& consensusParams = chainman.GetConsensus();
    if (block.nBits != GetNextWorkRequired(pindexPrev, &block, consensusParams))
        return state.Invalid(BlockValidationResult::BLOCK_INVALID_HEADER, "bad-diffbits", "incorrect proof of work");

    // Check timestamp against prev
    if (block.GetBlockTime() <= pindexPrev->GetMedianTimePast())
        return state.Invalid(BlockValidationResult::BLOCK_INVALID_HEADER, "time-too-old", "block's timestamp is too early");

    // Testnet4 and regtest only: Check timestamp against prev for difficulty-adjustment
    // blocks to prevent timewarp attacks (see https://github.com/bitcoin/bitcoin/pull/15482).
    if (consensusParams.enforce_BIP94) {
        // Check timestamp for the first block of each difficulty adjustment
        // interval, except the genesis block.
        if (nHeight % consensusParams.DifficultyAdjustmentInterval() == 0) {
            if (block.GetBlockTime() < pindexPrev->GetBlockTime() - MAX_TIMEWARP) {
                return state.Invalid(BlockValidationResult::BLOCK_INVALID_HEADER, "time-timewarp-attack", "block's timestamp is too early on diff adjustment block");
            }
        }
    }

    // Check timestamp
    if (block.Time() > NodeClock::now() + std::chrono::seconds{MAX_FUTURE_BLOCK_TIME}) {
        return state.Invalid(BlockValidationResult::BLOCK_TIME_FUTURE, "time-too-new", "block timestamp too far in the future");
    }

    // Reject blocks with outdated version
    if ((block.nVersion < 2 && DeploymentActiveAfter(pindexPrev, chainman, Consensus::DEPLOYMENT_HEIGHTINCB)) ||
        (block.nVersion < 3 && DeploymentActiveAfter(pindexPrev, chainman, Consensus::DEPLOYMENT_DERSIG)) ||
        (block.nVersion < 4 && DeploymentActiveAfter(pindexPrev, chainman, Consensus::DEPLOYMENT_CLTV))) {