PaddingScheme being !Send makes things harder

[gdesmott]

See librespot-org/librespot#1065

PaddingScheme is !Send making it impossible to use it in async code requiring Send futures.

Is there any way this could be prevented?

[tarcieri]

It's probably because the Box<DynDigest> members aren't Box<DynDigest + Send>.

@gdesmott alternatively you could use e.g. rsa::pkcs1v15::{SigningKey, VerifyingKey} or rsa::pss::{SigningKey, VerifyingKey} which are Send (+ Sync) maybe?

[gdesmott]

It's probably because the Box<DynDigest> members aren't Box<DynDigest + Send>.

Indeed, and it's quite easy to fix: #215