Support decrypting PKCS1 keys

[jadamcrain]

We're decrypting the pkcs8 keys using a crate designed to only handle pkcs8:

https://crates.io/crates/pkcs8

I don't see anything in the Rust ecosystem that can decrypt pkcs1 "out of the box". That said, the PEM file parser we're using can parse and expose the headers in the encrypted pcks1 PEM section....

Proc-Type: 4,ENCRYPTED
DEK-Info: AES-128-CBC,C335117F818B9FB719C75798A9063CDB

...which declares the content as encrypted and tells you the algorithm and initialization vector.

To implement it, we'd have to do our own password -> key derivation using those cryptographic primitives and support a number of common algorithms (e.g. AES-128-CBC).