Transaction IDs

The Lotus Tansaction ID is calculated differently than for BTC, BCH, or eCash. It includes what was a planned feature on Bitcoin Cash called "MalFix" or malleability fix for short. This basically means that the "Script Signature" is not covered by the transaction ID hash.

The purpose of this is to prevent the transaction ID from being mutable due to the fact that ScriptSig data is not covered by transaction signatures and may be modified by third parties. This is similar in intent to Segregated Witness, but is done for all transactions rather than only SegWit transactions.

This is resiable for two reasons:

  1. It allows the implementation of the lightning network
  2. Prevents third parties from executing malleability attacks which can cause transaction chains to become invalidated.

Instead of simply excluding the ScriptSigs from the calculation, the Lotus transaction ID is merklelized in order to allow more powerful scripting abilities such as miner-verified tokens. It additionally corresponds to the format of the Lotus Taproot Signature format. This allows a script to easily calculate it's own TxID for covenant verifications.

Format

SizeNameMeaning
4 bytesnVersionTransaction version
32 bytesnInRootMerkle root of the transaction inputs without the scriptSig included
1 bytenInHeightHeight of the input merkle root
32 bytesnOutRootMerkle root of the transaction out
1 bytenOutHeightHeight of the outputs merkle root
4 bytesnLockTimeTransaction locktime

C++ Example

uint256 TxInputsMerkleRoot(const std::vector<CTxIn> &vin, size_t &num_layers) {
    std::vector<uint256> leaves;
    leaves.resize(vin.size());
    for (size_t i = 0; i < vin.size(); i++) {
        CHashWriter leaf_hash(SER_GETHASH, 0);
        leaf_hash << vin[i].prevout;
        leaf_hash << vin[i].nSequence;
        leaves[i] = leaf_hash.GetHash();
    }
    return ComputeMerkleRoot(std::move(leaves), num_layers);
}

uint256 TxOutputsMerkleRoot(const std::vector<CTxOut> &vout,
                            size_t &num_layers) {
    std::vector<uint256> leaves;
    leaves.resize(vout.size());
    for (size_t i = 0; i < vout.size(); i++) {
        leaves[i] = SerializeHash(vout[i]);
    }
    return ComputeMerkleRoot(std::move(leaves), num_layers);
}

static uint256 ComputeTxId(int32_t nVersion, const std::vector<CTxIn> &vin,
                           const std::vector<CTxOut> &vout,
                           uint32_t nLockTime) {
    CHashWriter txid(SER_GETHASH, 0);
    size_t height;
    txid << nVersion;
    txid << TxInputsMerkleRoot(vin, height);
    txid << uint8_t(height);
    txid << TxOutputsMerkleRoot(vout, height);
    txid << uint8_t(height);
    txid << nLockTime;
    return txid.GetHash();
}
Edit this page on GitHub Updated at Sun, May 15, 2022