{"uid":"cap_oe7xkn3AUqLgzXMagFthL","slug":"sellat-proof-of-existence-sha-256-blockchain-anchoring-0acdda25","name":"Sellat Proof of Existence (SHA-256 Blockchain Anchoring)","description":"Timestamp and notarize any file or data by its SHA-256 hash: blockchain proof of existence and document integrity, anchored on Polygon in minutes and attested on Bitcoin (OpenTimestamps); blockchain notarization, not a notary act. Returns proof_id, certificate, proof.json and evidence ZIP, verifiable without Sellat. Use when you must prove that exact data existed by now and is intact.","url":"https://sellat.app/api/v2/proofs?utm_source=zero.xyz","method":"POST","headers":{},"bodySchema":{"type":"object","$schema":"https://json-schema.org/draft/2020-12/schema","required":["input"],"properties":{"input":{"type":"object","required":["type","method","bodyType","body"],"properties":{"body":{"type":"object"},"type":{"type":"string","const":"http"},"method":{"enum":["POST","PUT","PATCH"],"type":"string"},"headers":{"type":"object","additionalProperties":{"type":"string"}},"bodyType":{"enum":["json","form-data","text"],"type":"string"},"pathParams":{"type":"object","additionalProperties":{"type":"string"}},"queryParams":{"type":"object","additionalProperties":{"type":"string"}}},"additionalProperties":false},"output":{"type":"object","required":["type"],"properties":{"type":{"type":"string"},"example":{"type":"object"}}}}},"responseSchema":{"type":"json","example":{"id":"<proof_id>","hash":"<sha256>","next":"POST /api/v2/proofs/{id}/qualified adds the eIDAS qualified timestamp (RFC 3161) for 0.90 USD","urls":{"self":"https://sellat.app/api/v2/proofs/<id>","proof_json":"https://sellat.app/api/v2/proof/<id>.json","certificate":"https://sellat.app/certificate/<id>","evidence_zip":"https://sellat.app/api/v2/proofs/<id>/evidence.zip"},"state":"queued → anchored (minutes)","api_key":"<shown once: read-only key for this wallet’s proofs>","created":true,"payment":{"charged":true,"amount_usd":"0.01","transaction":"<tx hash on Base>"},"proof_id":"<proof_id: use it in POST /api/v2/proofs/{id}/qualified>","anchoring":{"policy":"fast"}}},"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.01","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"registry","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.01/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.01","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.01","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_OVW2PVrpNqF7d-oiImTtJ","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.01","costPer":"request","priority":0,"asset":null,"unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Anchors a SHA-256 hash on Polygon blockchain and attests it on Bitcoin via OpenTimestamps, returning a verifiable certificate, proof.json, and evidence ZIP","exampleAgentPrompt":"Can you create a blockchain proof of existence for this SHA-256 hash — 'a3f1c2d9e4b7082f1e6a5c4b3d2e1f0a9b8c7d6e5f4a3b2c1d0e9f8a7b6c5d4' — and give me a verifiable certificate anchored on both Polygon and Bitcoin?","exampleUseCases":[{"title":"Timestamping intellectual property before filing","prompt":"I've got the SHA-256 hash of my new software design document and I need to prove it existed today before I file the patent — can you anchor this hash 'b4e2f1a0c3d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b7c8d9e0f1' on the blockchain and get me a certificate?"},{"title":"Legal evidence preservation for a contract","prompt":"We need to preserve proof that this contract draft existed at today's date — please timestamp the SHA-256 hash 'c5f3e2b1a0d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0' on Polygon and Bitcoin and return the proof.json and certificate."},{"title":"Audit trail for compliance records","prompt":"Our compliance team needs a blockchain-anchored timestamp for this audit log file's SHA-256 hash '1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b7c8d9e0f1a2b' — please submit it to Sellat and get back the verifiable certificate and evidence ZIP."}],"resultDescription":"Returns a verifiable proof certificate, a proof.json file, and an evidence ZIP containing the blockchain anchoring on Polygon (within minutes via fast batch) and a Bitcoin attestation via OpenTimestamps. All outputs are independently verifiable without relying on Sellat's infrastructure.","failureModes":["Invalid or malformed SHA-256 hash input returns a 400 error","Payment failure via x402 protocol prevents proof creation","Polygon network congestion may delay batch anchoring beyond stated minutes","Duplicate hash submission may return existing proof or create new timestamp","OpenTimestamps Bitcoin attestation may be delayed due to Bitcoin block times"],"whenToPreferThis":"Choose this endpoint when you need a low-cost ($0.01 USDC), fast, multi-chain proof of existence that is independently verifiable without trusting Sellat — combining Polygon's speed with Bitcoin's security via OpenTimestamps. Prefer over eIDAS/RFC 3161 timestamps when you want decentralized blockchain anchoring rather than EU qualified trust service provider signatures.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-23T18:30:22.953Z","isFirstParty":false,"canonicalSlug":"sellat-proof-of-existence-sha-256-blockchain-anchoring-0acdda25"}