Gnus v5.13 (from emacs v24.4) fails to encrypt messages with gnupg
2.1.0.

The reason for this is that freshly released gnupg 2.1.0 changed the
output slightly:

$ gpg-filter --with-colons --no-greeting --batch --with-fingerprint \
  --fixed-list-mode --list-keys "Matthias Maier"

  pub:u:4096:1:B5A4E06FBD3A97A3:1242087539:1468755388::u:::scESC::::::

older verions produced

  pub:u:4096:1:B5A4E06FBD3A97A3:1242087539:1468755388::u:::scESC:

instead. With the additional five empty colons ":::::", however,
epg--list-keys-1 returns additional arguments which let egp-list-keys
fail:

  epg-list-keys: Args out of range: ["pub" "u" "4096" "1"
  "B5A4E06FBD3A97A3" "1242087539" "1468755388" nil "u" nil ...], 15

So, a more robust filtering in epg--list-keys-1 might be necessary.

Best,
Matthias