Publication

GuardTime Publication with the Integrity Code is the basis for evidence generation as the timestamp is cryptographically related to all the newspaper publications that have appeared after its generation.

GuardTime publishes the Integrity Code once a month in newspapers distributed worldwide. A new Integrity Code for the Calendar is generated by GuardTime at the 15th day of every month at 00:00:00 UTC time. The code is printed in newspapers within the next 5 days depending on the publishers’ schedules.

The Integrity Code published in newspapers contains a hash value and a date and time record. The hash value is an aggregate hash summary of all the hash values of the GuardTime Calendar since the beginning of the Calendar until the published date and time.
Since every hash value recorded in the Calendar is an aggregate hash summary of all the digital content registered during the given 1-second interval, the newspaper publication cryptographically summarizes all the digital content registrations by GuardTime since the start of the timestamping service. As a cryptographic summary of the digital history, the newspaper publication serves as a reliable reference for verification under the assumption that the integrity of the newspaper can be reliably established.

You do not need to keep archives of newspapers for future verification. There are public institutions like libraries and archives that archive newspapers and collectively guarantee their integrity.