No, you don't need blockchain for that, just a good old RFC 3161 timestamping server, most big CAs run one and timestamp stuff for free. Actually secure timest

No, you don't need blockchain for that, just a good old RFC 3161 timestamping server, most big CAs run one and timestamp stuff for free. Actually secure timestamping is already used by Windows to verify software signatures, even when the signing key expires: https://security.stackexchange.com/questions/47289/how-is-an-authenticode-timestamp-verified https://security.stackexchange.com/questions/47289/how-is-an... Heck, you can even use Roughtime [0] to achieve secure timestamping as it uses digital signatures and allows you to provide a nonce. Even the design doc [1] mentions this use case: > This means that Roughtime replies can be used as a time-stamping service, and thus that Roughtime servers can be used to check each other. [0]: https://blog.cloudflare.com/roughtime/ https://blog.cloudflare.com/roughtime/ [1]: https://roughtime.googlesource.com/roughtime https://roughtime.googlesource.com/roughtime