Creating A Timestamp
Before a timestamp-service commences operations, the Time Stamp Authority calibrates its clock(s) with an upstream time source entity, such as a legally defined master clock for the jurisdiction the TSA is time-stamping evidence for. When trusted time has been acquired, the TSA can issue timestamps for unsigned and digitally signed data based on all of the jurisdictions it maintains timing solutions for.
Applications using timestamps on unsigned data can provide evidence to a verifier that the underlying digital data has existed since the timestamp was generated.
When a requestor requires a timestamp for a dataset, it creates a cryptographic or arithmetic hash function of the data. The Hash Function produces a unique string of data which represents the totality of the content in a compact form, i.e. it forms a snapshot of the content. The hash is transmitted through a network connection to the TSA and the time-stamp is issued as a secured digital token token, which is returned to the requestor for association with the data sent to the TSA to memorialize.
For applications using digitally signed data, the requestor signs the digital hash with its private key and submits the digital signature to the TSA, which performs the same operations as in the previous example: bind the submitted data with a timestamp using its cryptographic binding and return the results to the requestor.
When the requestor receives the timestamp token from the TSA, it also optionally signs the token with its private key. The requestor now has evidence that the data existed at the time issued by the TSA. When verified by a verifier or relying party, the timestamp token also provides evidence that digital signature has existed since the timestamp was issued, provided that no challenges to the digital signature's authenticity repudiate that claim.
Timestamp tokens in open timestamping models can be obtained from different TSAs on the same data and can be verified at any time by a third party.
Read more about this topic: ANSI ASC X9.95 Standard
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