Docs

Overview

Cypher runs your sends and swaps through a zero-knowledge shielded pool on Solana. You shield coins into the pool, where they become a note only your key can read. When you spend, a proof built in your browser shows you own a note without saying which, and the pool pays out. Nothing on chain joins the deposit to the payout.

• Zero knowledge. The proof reveals that a note is yours, not which note.
• No custody. Only your key can spend your notes. It never leaves your browser.
• A real crowd. Hundreds of thousands of notes in the SOL pool alone.

How the pool works

It works the way Zcash’s shielded pool does. Cypher uses the pool run by Privacy Cash’s Solana program (9fhQBbumKEFuXtMBDw8AaQyAjCorLGJQiS3skWZdQyQD).

1. Notes. A deposit becomes a note: a commitment added to a Merkle tree, with its amount encrypted to your key.
2. Proofs. To spend, your browser proves in zero knowledge that you own an unspent note somewhere in the tree.
3. Nullifiers. The proof also publishes the note’s nullifier, a tag that stops it being spent twice without identifying it.
4. Relayer. Privacy Cash’s relayer submits the withdrawal and pays its network fee, so your wallet never appears in it.

Shield

Shielding is a deposit from your wallet, the one step your wallet signs. It’s public: anyone can see your wallet put an amount into the pool. It’s also the last thing on chain tied to you.

1. Connect a wallet and unlock your shielded balance (one signed message).
2. Pick SOL, USDC or USDT and an amount.
3. Sign the deposit. The note shows up under Shielded once the pool has indexed it.

Send

Pay SOL, USDC or USDT out of the pool to any address. Hold the button to confirm: there’s no wallet prompt, because your wallet takes no part in it. From your wallet instead, Send shields first and pays out right after; see Good practice for why that’s weaker.

Swap

A swap is paid from the pool to a one-time wallet your browser makes for that swap alone. It trades at the best route Solana’s aggregators offer, sends the output to you or anyone you choose, hands over whatever SOL it has left, and ends empty. On chain it reads as a stranger’s swap.

• Fees. A SOL swap keeps 0.005 SOL back for the one-time wallet’s fees. A USDC or USDT swap also draws the pool’s smallest SOL payout for them. Whatever isn’t spent goes to the recipient.
• Never stranded. The one-time wallet’s key is sealed with your pool key and kept in your browser until it has delivered. If a tab closes midway, it shows under Shielded with Finish the swap.

Your pool key

Your shielded balance is opened by your wallet’s signature over a fixed message. That signature is the key: it reads your notes and spends them. Cypher keeps it in the tab’s memory only and asks again on your next visit.

• Same key everywhere. It’s the message Privacy Cash’s own app uses, so a balance shielded there shows up here.
• Checked once. The first time, your wallet signs twice. A wallet that signed differently each time would lose its notes, so Cypher won’t open it.

Fees and limits

One payout spends at most two of your notes. If your balance is spread across many small notes, the largest you can send at once is your two biggest notes together; shielding again merges notes.

Custody and trust

Cypher never holds funds. The pool is Privacy Cash’s program; Cypher doesn’t run it and can’t move a note. Every proof is built in your browser with Privacy Cash’s own SDK.

• The relayer sees requests. It handles each payout, so it sees the recipient, the amount and the IP address the request came from. It can’t tell which deposit paid, and it can’t spend your notes.
• Deposits are screened. Privacy Cash screens depositing wallets and may turn some away.

Good practice

The proof hides which note paid. Amounts and timing can still give it away.

• Leave time. Shielding 5 SOL and paying out 4.98 SOL a minute later is easy to pair. Shield ahead and spend later.
• Vary amounts. Spend amounts that don’t mirror what you shielded, and avoid unique figures like 13.37.
• Don’t come home. Unshielding back to the wallet you shielded from ties the two ends together again.

FAQ