What is an L2 ZSA?

An L2 (layer-two) Zcash Shielded Asset is an asset built on top of Zcash, using only what Zcash already provides, rather than by changing Zcash. It is how Zecboat's postcards exist on Zcash mainnet today.

1. An ordinary note with a name attached

Every L2 ZSA is one ordinary shielded ZEC note of a small, fixed size, carrying an encrypted memo that names it. It is not a token contract and not a second chain. To the network it is just a shielded note; your wallet reads the memo and shows you the postcard.

2. Sending one

Sending the asset spends that exact note and writes the memo, byte for byte, onto the new one. Custody moves; identity does not. Because it is an ordinary shielded note underneath, it inherits Zcash's privacy exactly, with no new cryptography in the transfer itself.

3. Who says it is genuine

Anyone can copy a memo, so the memo alone proves nothing. Three things do:

• The asset id is bound to the issuer. Under ZMAP identity v1, each id is computed from the collection's key and the item's description, and the description carries the image's SHA-256. Without the issuer's key, a matching id cannot be made.
• The collection is closed on chain. The issuer writes a signed list of the items onto the chain. Anything issued after that fails the check.
• It is registered. The collection is listed in the Zecboat Registry, which lives on the chain itself, so any wallet can find it without asking a website.

The Zecboat wallet's Check runs these from the chain. Wake goes one step further and traces the postcard you hold back to its mint, without revealing who held it in between. Wake is not yet externally reviewed.

4. What Zcash does and does not do for it

• Zcash balances ZEC, not your asset. Supply is closed on chain and anyone can count it, but the network itself does not refuse an extra issuance. It is visible, not impossible.
• It is best for items held whole. A currency splits and merges; a split leaves one half without a trail. L2 ZSAs suit postcards, editions, certificates and memberships, not stablecoins.
• It needs a wallet that knows about it. An ordinary wallet sees a small note and may sweep it into a payment. Zecboat locks asset notes so they are never spent by accident.

The short version

An L2 ZSA is a shielded ZEC note with a name attached, made trustworthy by the issuer's key, a closed collection and the Registry, all on the chain. It works on Zcash today because it asks nothing new of Zcash. Read more on Layer-Two Shielded Assets and in the protocol.