[dane] case sensitivity and draft-ietf-dane-smime / draft-wouters-dane-openpgp

[Paul Wouters <[e-mail]>]

It was brought to my attention by Matthias Wimmer that we overlooked
an important issue with respect to the base32 generation of the base32
encoded left hand side of the email address.

Mail servers and mail clients do not treat email addresses as
case-insensitive. When encoding an LHS with base32, the case matters.
Using the wrong case will cause you to not find the SMIMEA / OPENPGPKEY
record.

paul@bofh:$ python
Python 2.7.3 (default, Aug  9 2012, 17:23:57) 
[GCC 4.7.1 20120720 (Red Hat 4.7.1-5)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import base64
>>> base64.b32encode("paul")
'OBQXK3A='
>>> base64.b32encode("Paul")
'KBQXK3A='
>>>

We should probably add a section explaining this, and perhaps suggest to
lowercase before base32'ing the LHS for the lookup.

Paul