Privacy and trust
The trust assumption
Arcium splits every secret value into shares held by the cluster's nodes. A position stays private as long as the nodes do not collude to reconstruct it. Nothing on the path holds your side, size or liquidation price in the clear, including the SHROUD program and its operators.
The book key
Each book slot is encrypted on its own, so one open can write one slot. Every slot is encrypted to a fixed x25519
public key that nobody holds the private key of: the first sha256("SHROUD book key v1 #i") (top bit cleared)
that is a point on Curve25519, multiplied by 8 so it lies in the prime-order group. Only the cluster can decrypt a
slot, exactly as with Arcium's own Enc<Mxe> type, but the nonce can travel apart from the ciphertext, which lets
one check round read 128 slots from a single account range.
What an observer learns, and when
| Event | What becomes public |
|---|---|
| Open | collateral, entry time and price, slot, whether the open obeyed the rules |
| Check round | one bit per slot at the oracle price used: 1 only for slots past their line |
| Liquidation | that the slot was past its line at that price |
| Close | the payout, from which the final profit or loss follows |
A slot that answers 0 round after round tells an observer only that its line has not been crossed yet. The earlier privacy measurement guessed the side of hidden positions from everything public at 44.5% to 48%, no better than a coin.
What you keep
Your browser keeps the plain record of what it sealed (side, size, threshold), so it can show your own position. The chain keeps only ciphertext.