Transparent Transactions

Transparent Transactions are very similar to Bitcoin.

If you have a good understanding of the Bitcoin data model, you can safely skip this section. Otherwise, here's a recap.

Transactions have inputs and outputs. Outputs are payment recipients and are expressed as:

  • a destination address,
  • an amount (in ZEC or zats1)
  • and a memo2

This is also called a note.

Inputs are previous outputs that have not been used yet.


It is forbidden to use or spend the same output twice!

Unlike outputs, inputs are not specified by their properties. Instead, inputs are references to previous transaction outputs. An input is a transaction ID3 and an output index.

This way, a validator can keep track of the unspent transaction outputs in a database and mark them spent when it sees a transaction that refers to them.

Validation Process

The validation process is approximately:

  • Check that outputs have a valid address and amount4;
  • Check that inputs are valid. They must refer to previous unspent transaction outputs (UTXO);
  • Collect the amount associated with the inputs as part of the previous step;
  • Check that outputs do not exceed inputs in value. The transaction cannot create funds5. Any difference are fees that are given to the miner;
  • Check that the inputs have valid signatures. signatures insure that only the person who received the funds is able to spend them.

Transaction Graph

Transactions form a acyclic graph that has links between UTXO, i.e. notes.

Here's how a portion of the Bitcoin Graph could look like:



  1. There are 100 000 000 zats per ZEC

  2. Technically, transparent outputs do not have memos for legacy reasons. We'll assume they have just to be consistent with shielded transactions.

  3. Transaction ID are hashes of transactions

  4. The protocol only validates that the values are well-formed, aka the amount is not negative, not too big, etc. But it cannot verify that the address has a known secret key...

  5. The coinbase transaction where miners collect their reward is an exception. But we will omit them for now.