Glossary

These pages assume Zcash vocabulary, and much of who reads them works on Solana. The words are written down here instead of implied.

From Zcash

Note

One unit of shielded value: an amount, a recipient and some randomness. A shielded balance is a set of notes rather than a number, which is why a proof speaks about one of them.

Note commitment

A hash of a note, published on chain. It says nothing about the note, and it is what the tree is made of.

Commitment tree

An append-only Merkle tree holding every commitment the pool has ever taken. Membership in it is the thing a proof proves.

Anchor

The root of that tree at one block. A proof is built against one anchor, so it is a statement about that block and never about now.

Frontier

The right edge of the tree at a height, thirty-two nodes standing for every commitment before it. Starting a walk from one is how a wallet avoids replaying the whole pool.

Witness

The siblings along the path from a note's commitment up to the root. They are mostly other people's commitments, which is why building one costs a walk rather than a lookup.

Nullifier

A value published when a note is spent, so the network can refuse to spend it twice. Until that moment nothing links it to the note.

Action

One slot in a shielded transaction, carrying a spend and an output together. Scanning cost is counted in actions rather than in transactions.

Pool

A shielded accounting system with its own tree, its own nullifier set and its own value balance. Sprout, Sapling, Orchard and Ironwood are four of them.

Turnstile

The rule capping what leaves a pool at what verifiably entered it. It is what held the Orchard bug to one pool instead of letting it inflate the chain.

Shielded and transparent

Transparent funds sit at an address anybody can read. Shielded funds sit in a pool, where only a key holder can see them.

Viewing key

A key that reads an account's notes without being able to spend them. A full one reads everything, forever, which is why disclosure needs something narrower.

Spending key

The key that can spend. It never leaves the browser, and a proof needs it, which is why proving cannot be handed to a server.

Memo

512 encrypted bytes carried by a shielded output, opened by the recipient's key and nobody else's.

From Zolar

Tag

A value derived from the same secrets as the nullifier and separated from it by a domain. It lets Solana see one note used twice without anybody publishing the nullifier.

Attestation

The Solana account this writes: a claim, the anchor it was checked against, an expiry, and whose it is. It cannot be transferred or traded.

Attester quorum

The set that asserts what the Ironwood tree looked like and signs for a proof against it. Solana cannot follow Zcash consensus, so somebody has to say.

The relay

One binary carrying queries between a browser and a Zcash light node, because a browser cannot reach one directly. It never sees a key.