[JWett]

Surety is not a trusted central authority. There is no mathematically feasible way to backdate a document and weave it into the chain. The only way to circumvent the system would be to generate the same submitted hash value (using two different hash algorithms) with a different document. Additionally, for it to be actually useful, you would need to generate a hash collision for a different document with a purposeful modification (for example, changing the amount due for an invoice.) I can't begin to calculate the odds on making that happen.

Also note the hash values sent to Surety were calculated on the end user's computer. Surety never sees the actual file being timestamped.

As for the safety deposit box metaphor, the Haber-Stornetta approach is akin to nailing the hash to a post in the town square.