Distributed FROST Silent Payments. BlackIce lets a hardware multisig pay a silent-payment address, with every step coordinated over an end-to-end encrypted Marmot group and no server in the middle.
The problem
Silent payments (BIP 352) give the recipient one static address that can‘t be linked on-chain, but until now only single-key wallets could pay one. Sending needs the combined private key of every input, and a multisig split across devices never has that in one place. Multisig coordination also leaks: co-signers pass transactions over Signal, email or coordinator servers.
What we built
- Silent payments from a hardware multisig: each Frostsnap device contributes its own ECDH share with a BIP 374 DLEQ proof, and the shares combine into the payment output. No key leaves its device.
- FROST threshold signing: any k-of-n devices produce one Schnorr signature. On-chain it’s an ordinary single-key taproot spend.
- Marmot as the only transport: every ceremony message is MLS-encrypted over Nostr. Relays see only ciphertext, and there are no phone numbers or servers.
- Safety checks: each device shows the silent-payment address and amount before signing, and no signature share is released until every signer has derived the identical transaction.
It works
Two Frostsnap devices on two laptops paid 1,000 sat to a tsp1… address: confirmed on Signet, block 329,605. The relays saw 12 encrypted events and no plaintext.
Built on Frostsnap PR #640, marmot-ts and Nostr. Signet only; development firmware.
Team: Robos & Rademenez