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No signature company to trust. Forward the document, type "I sign this document", and your email provider's DKIM signature, the one that already authenticates your mail, signs it.
The proof is one self-contained file anyone can verify offline in a browser: no account, no app, it holds up even if we disappear. We never hold a key, so we can't forge or alter anything.
Open source, Apache-2.0: self-host from github.com/kychee-com/kysigned, or use the hosted version at kysigned.com. Start with 4 free, then $0.25 a document, no subscription.
Built by Kychee, the AI-native software factory (kychee.com).