TODO

backends:
    partial, e.g. apply padding and let actual implementation generate a signature; can be used by other backends
    textbook, e.g. c = m^e%n; load/save/generate keys from/to pem/der using asn1crypto
    hashlib (python stdlib)
    cryptography
    pkcs#11; use sub process? or cffi?
    openpgp smartcard via different transports; create generic smartcard en/de coder
    some clouds
    pynacl


# XXX https://en.wikipedia.org/wiki/Integrated_Encryption_Scheme
# XXX https://en.wikipedia.org/wiki/ElGamal_encryption
# XXX https://en.wikipedia.org/wiki/ElGamal_signature_scheme
# XXX ECDSA? What about ED? Stuff encryption and signatures into the same class?


API to get supported algorithms, ciphers, etc.

- openssl genpkey -algorithm rsa-pss