[JWett]

"Hash and Sign" timestamping is flawed in that it relies on the trust of a central authority. An insider with access to the private key could easily backdate a timestamp and sign any document/timestamp combination. Surety's widely-witnessed approach was meant to fix this issue.

Chaining the hash values made it fundamentally impossible for any malicious actor to generate a notary certificate for a future document that would roll up and produce the correct super hash value that is woven into the chain.