MPC £100k secure threshold
Set each party’s private income and run the secure threshold: the page reveals only the yes/no verdict bit — not any salary, and not even the exact total — and the share matrix shows exactly what crosses the wire.
How it works & full security caveat
Four flatmates want a £100k mortgage together. The lender needs only one bit: does their combined income clear £100,000? Secure multi-party computation lets them jointly compute that bit without anyone disclosing a salary. Each party splits its value into random shares (any single share is a uniform random number that leaks nothing), addition is free over shares, and a secure comparison opens only the boolean total ≥ £100k — never the total itself. This mirrors the native sparq-mpc crate (30k + 28k + 26k + 24k = 108k → true).
What this demo is, and is not. This page is a client-side illustration of the protocol shape, not the hardened crate running in your browser — the sparq-mpc crate is deliberately native-only and absent from the wasm bundle, so nothing cryptographic runs here. The in-tab code uses simple additive (n-of-n) secret sharing with Math.random to make the “shares reveal nothing” / “addition is free” properties visible; the real crate uses honest-majority Shamir t-of-n sharing and a bit-decomposition secure comparison.
Even the native crate makes no production security claim. It is honest-majority semi-honest only — confidentiality holds against parties that follow the protocol but try to learn more, not against actively-cheating (malicious) parties, and assumes an honest majority. The collaborative zero-knowledge proof of correctness and source-attestation layer is a stub that returns NotYetImplemented (beads sq-9hrn / sq-qhy4), so this demo does not prove the result is correct — there is no soundness guarantee, only that the disclosure pattern is minimal under the semi-honest, honest-majority assumption. No external cryptographer has reviewed sparq’s bespoke MPC; treat it as a research / explainer artifact, not a certified secure-computation system.