Add support for different key types and algorithms

[TimoGlastra]

Would be great if the library could support other key types and algorithms that are supported on iOS and Android platforms.

For iOS e.g. there is support for CryptoKit in which you can use other key types besides P-256: https://developer.apple.com/documentation/cryptokit

Android also supports more key types in their hardware keystore I believe: https://source.android.com/docs/security/features/keystore/features