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.
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...
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/
[1]: https://roughtime.googlesource.com/roughtime