pyca/cryptography — pull request #327 by reaperhulk (2013-12-21 23:33:07+00:00)
Title: Restrict GCM tag length to 4+ bytes

OpenSSL will cheerfully let you pass down to 1 byte. NIST vectors only go down to 4 bytes, so this patch requires 4+ bytes passed and adds a note to the docs about it.