The extension never sends your conversation to Sigill. Here is what happens locally in your browser:

1. The prompt and response are combined into an evidence envelope.
2. The envelope is serialised using JCS (RFC 8785) — a canonical JSON format that produces a byte-for-byte identical output on any device.
3. A SHA-256 hash of those bytes is computed — a 64-character fingerprint that uniquely identifies the content without revealing it.
4. Only the hash is sent to a RFC 3161 Timestamp Authority, which signs it with a trusted certificate and returns a timestamp token.
5. The token is stored locally alongside the envelope. The timestamp proves the conversation existed at that moment, and the hash lets you verify the content was never altered.

The TSA only ever sees a cryptographic hash — mathematically impossible to reverse into the original text.