Use a better password-based KDF for controller passwords, authority identity key encryption, and more
With the ed25519 key transition, we'll want to start bringing offline identity keys to regular relay operators (and ideally hidden service operators too somehow, if we can figure out a non-stupid way for it to interact with legacy/trac#8106 (moved)).
As we do this, we'll want a better password-based KDF. Right now we have the very silly "NID_pbe_WithSHA1And3_Key_TripleDES_CBC" for protecting authority keys, and the very silly OpenPGP KDF for hashing controller passwords. Let's do something from the 21st century.
This is a bikeshed discussion. I nominate: "Derive keys with scrypt-jane, with salsa20/8 and SHA512."