[openpgp] details of 4880bis work

[Stephen Farrell <[e-mail]>]

Hiya, here's the 2nd thread, starting from DKG's list. Please
discuss... (We don't need +1's for this, just tweaks, corrections,
additions etc.) If someone wanted to put this on github or
somewhere else the group can edit it, that'd also be fine.

Ta,
S.

a) update the fingerprint format (avoid inclusion of creation date, use
   stronger digest algorithm; i'm dubious about embedding algorithm
   agility in the fingerprint itself, but explicit version info in the
   fingerprint might be reasonable so we don't have to keep guessing by
   fpr structure for future versions)

b) get rid of keyids entirely -- when referring to a key, use the
   fingerprint where a compact hint is needed (e.g. in a replacement of
   the issuer subpacket) or the full primary key where it is more
   sensitive (e.g. in designated revoker).  With EC keys, we could
   consider using the full key (not the full cert) even in the issuer
   subpacket case, which could make things cleaner.

c) deprecate MD5, SHA1, and RIPEMD160

d) clarify that cleartext signatures should all use charset/encoding
   UTF-8.

e) update S2K with something more modern (PBKDF2, HKDF, scrypt?),
   deprecate all the other mechnanisms explicitly

f) standardize the two new curves coming out of the CFRG: 25519 and
   curve448 ("goldilocks") for both signatures and encryption (Werner
   has already started this process for 25519 signatures)

g) remove compression entirely

h) clean up the language: clearly distinguish between "public key" and
   "certificate", and ensure that the use of the terms "trust" and
   "validity", if still present, are used unambiguously.

i) declare a literal data packet type "m" that means "MIME content" so
   that we can punt on the rest of the message
   structure/format/encoding/type craziness to MIME.

j) deprecate 3DES, IDEA, and as many of the weaker ciphers as we can
   get away with.

k) provide a modern streamable/chunkable AEAD replacement for
   Symmetrically-Encrypted Integrity-Protected Data (SEIPD) packets

l) change MTI algorithms: SHA512, the two new ECs, and the new AEAD
   mechanism should be the baseline.