Module hash

Transaction identifiers for Zcash.

Zcash has two different transaction identifiers, with different widths:

• Hash: a 32-byte transaction ID, which uniquely identifies mined transactions (transactions that have been committed to the blockchain in blocks), and
• WtxId: a 64-byte witnessed transaction ID, which uniquely identifies unmined transactions (transactions that are sent by wallets or stored in node mempools).

Transaction version 5 uses both these unique identifiers:

• Hash uniquely identifies the effects of a v5 transaction (spends and outputs), so it uniquely identifies the transaction’s data after it has been mined into a block;
• WtxId uniquely identifies the effects and authorizing data of a v5 transaction (signatures, proofs, and scripts), so it uniquely identifies the transaction’s data outside a block. (For example, transactions produced by Zcash wallets, or in node mempools.)

Transaction versions 1-4 are uniquely identified by legacy Hash transaction IDs, whether they have been mined or not. So Zebra, and the Zcash network protocol, don’t use witnessed transaction IDs for them.

There is no unique identifier that only covers the effects of a v1-4 transaction, so their legacy IDs are malleable, if submitted with different authorizing data. So the same spends and outputs can have a completely different Hash.

Zebra’s UnminedTxId and UnminedTx enums provide the correct unique ID for unmined transactions. They can be used to handle transactions regardless of version, and get the WtxId or Hash when required.

Structs

• Hash
  A transaction ID, which uniquely identifies mined v5 transactions, and all v1-v4 transactions.
• WtxId
  A witnessed transaction ID, which uniquely identifies unmined v5 transactions.