affine backend backends Backends Blowfish boolean Botan Changelog ciphertext committer committers conda crypto cryptographic cryptographically Debian decrypt decrypted decrypting deserialize deserialized Docstrings fernet Fernet hazmat indistinguishability interoperable introspectability invariants iOS Koblitz metadata pickleable plaintext pseudorandom Schneier scrypt testability Ubuntu unencrypted unpadded unpadding