When you publish or update a post, DateSealed calculates a SHA-256 hash of the post text (and, optionally, the featured image file) on your server and sends only that hash to the DateSealed service. The service returns a signed time stamp (RFC 3161) immediately and anchors the hash in a Bitcoin block through OpenTimestamps within hours. Anchored records can be verified from the Bitcoin ledger alone, even if the service disappears.

Automatic: a new record on every publish and update; earlier records are kept as a history.
Private: the text, images and URLs of your posts are never sent.
Badge: a small line after the post with the record date and a link to the record page (you can turn it off).
Admin: a “DateSealed” column in the post list and a box on the edit screen.
Record pages in the language of your site: the badge links to the record page in all the languages datesealed.com offers (50 at the time of this release); other locales get the English page.

Records made with this tool do not guarantee legal effect. If you need an accredited timestamp (certified by Japan’s Minister of Internal Affairs and Communications), please use an accredited provider.

External service

This plugin connects to the DateSealed service (https://datesealed.com), operated by Lightscend Co., Ltd., to create and check records.

What is sent: the SHA-256 hash (64 hexadecimal characters) of the post text, and optionally of the featured image file; the site URL appears in the User-Agent header of every request. Nothing else.
When: when a post is published or updated (sent from WP-Cron shortly afterwards; if the hourly limit is reached, later), when you click “Record now”, and twice a day to ask whether pending records have been anchored.
Terms and privacy: https://datesealed.com/terms