Let's Seal introduces an open standard called SEAL (Sealed Evidence Anchored to a Ledger) to provide tamper-proof proof for any file. This initiative aims to democratize file verification, making it free and accessible, akin to how Let's Encrypt revolutionized TLS certificates.

When a file is sealed using Let's Seal, three independent proofs are generated: a signature from a certificate authority, a record appended to an RFC 6962 transparency log, and a SHA256 timestamp anchored to the Bitcoin blockchain via OpenTimestamps. This combination ensures integrity, transparency, and a verifiable timestamp without relying on any single proprietary service.

Verification is designed to be universally accessible. Sealed PDFs use standard PAdES signatures verifiable by any PDF reader, while sealed artifacts include cosign-compatible signatures and SLSA attestations. The system offers three usage tiers: a free web app backed by Backblaze, a self-hostable option, and programmatic access via a CLI tool (sealbot) and API, similar to Let's Encrypt's Certbot. The project is open-source under the Apache-2.0 license.