I've fixed the parameter validation of all plugins in the
CryptographyPlugins package and removed SHA256Plugin because
SHA2Plugin does the same and more.
I ran the tests of the Cryptography package on my machine (64-bit linux)
and all of them passed (except for those using SHA256Plugin obviously).
Please review and test the code, and if everything looks good, I suggest
adding all plugins as external to the official VMs.