STAC may refer to: Computers and electronics stac (Set AC Flag) instruction on x86 CPUs, part of Supervisor Mode Access Prevention Stac Electronics, a former American technology company Lempel–Ziv
1. Compute SHA-256 of OTSCanonicalRecord value → must equal OTSHash 2. Open OTSProofURL → extract Bitcoin block number → must equal OTSBitcoinBlock 3. GET OTSBitcoinBlockVerifyURL → returns the Bitcoin block hash at height OTSBitcoinBlock; GET https://blockstream.info/api/block/{that hash} → its timestamp must match OTSTimestamp 4. Read CopyrightID inside OTSCanonicalRecord → must equal the CopyrightID above 5. GET OTSVerificationAPI → pre-computed 6-check result from server 6. If all match: this entity was registered on CopyrightChains at OTSTimestamp, independently verifiable on Bitcoin Note: an OTS proof may carry multiple Bitcoin attestations; OTSBitcoinBlock is the earliest confirmed one — a later attestation inside the proof corroborates it and is not a mismatch
Dual-chain trust anchor. Chain 1 (CopyrightChains): CopyrightID 0x6e908e80b28ea0d4f294002aef6f10567aa834f22ab61617b86af819d5e1b67b. Chain 2 (Bitcoin): anchored in block 953407 (2026-06-12T19:24:56Z). Bridge: the canonical record inside this Bitcoin proof contains the same CopyrightID. Verify: download https://artists.proofprofile.net/proofs/artist/598397bb-e061-479f-bd26-1f96ab6b574f.json and https://artists.proofprofile.net/proofs/artist/598397bb-e061-479f-bd26-1f96ab6b574f.ots, run `ots verify -f record.json proof.ots` (https://opentimestamps.org).