RSA

It would be great to have support for parsing PEM, DER, etc, and to be able to do encryption and decryption operations on them (possibly using platform-specific libraries like BouncyCastle or a pure Kotlin implementation).

Annoyingly, this would require two new deps - BigInteger and Base64. BigInteger is easily available from https://github.com/gciatto/kt-math (a really good library). It would also be great if Korlibs could make a Base64 library in multiplatform, as this is really lacking from the standard library. It is a really great example for the `when` clause instead of indexOf.

Begin by defining the supported PEM and DER inputs and the encryption and decryption operations described in the issue. Compare the proposed BouncyCastle or pure Kotlin approaches, and assess the BigInteger and Base64 dependencies, including kt-math. Done means the scope, platform strategy, dependencies, and verification cases are agreed.

Written by the indexing model from the issue text.