[REQ] Minor fixes for code optimisation, fix nonce generation to be secure

[amasses]

Is your feature request related to a problem? Please describe.

While reviewing this code I have noted a few issues such as:

• Inconsistent use of OpenSSL::Digest vs Digest
• Unnecessary calls to convert Time to UTC before getting the UNIX timestamps
• Insecure nonce generation

Describe the solution you'd like

These issues should be resolved - I will submit a PR for these issues.

Describe alternatives you've considered

There are no alternatives

Additional context

None