Resent from my DocuSign email address :/

Cordialement,
Erwann Abalea

Le 21 mars 2016 à 15:50, Erwann Abalea 
<[email protected]<mailto:[email protected]>> a écrit :

Bonjour,

X.509 has recently changed its definition of what is admissible in a dNSName 
entry. You can freely download all this from 
https://www.itu.int/rec/T-REC-X.509/en.

From the very first edition of X.509v3 (1997) up to the latest revision (2012), 
it was defined as:

  *   the dNSName alternative is an Internet domain name defined in accordance 
with IETF RFC 1035;

preventing the use of anything other than letters, digits, and hyphen.

A published corrigendum changed the definition to:

the dNSName alternative shall be a fully-qualified domain name (FQDN). The 
domain name shall be in the syntax as specified by section 2.3.1 of IETF RFC 
5890 meaning that a domain name is a sequence of labels in the letters, digits, 
hyphen (LDH) format separated by dots.

A label may be in one of two formats:

a)  All characters in the label are from the Basic Latin collection as defined 
by ISO/IEC 10646 (i.e., having code points in the ranges 002D, 0030-0039, 
0041-005A and 0061-007A) and it does not start with "xn--". The maximum length 
is 63 octets.
b)  It is an A-label as defined in IETF RFC 5890, i.e., it starts with the 
"xn--" and is a U-label converted to valid ASCII characters as in item a) using 
the Punycode algorithm defined by IETF RFC 3492. The converted string shall be 
maximum 59 octets. To be valid, it shall be possible for an A-label to be 
converted to a valid U-label. The U-label is as also defined in IETF RFC 5890.

NOTE 1 – An A-label is normally not human-readable.

Again preventing anything other than letters, digits, and hyphens.

Cordialement,
Erwann Abalea



Le 21 mars 2016 à 14:08, Peter Bowen <[email protected]<mailto:[email protected]>> a 
écrit :


On Mar 21, 2016, at 4:39 AM, Gervase Markham 
<[email protected]<mailto:[email protected]>> wrote:

On 21/03/16 11:23, Rob Stradling wrote:

Are the things we put in certificates hostnames? Given that SSL is for
connecting to internet hosts, it would seem to me that they are. Clue me
in by explaining what I'm missing.

"You've entered a special hell. It is dark and scary. You are likely to
be eaten by a grue."

https://www.mail-archive.com/[email protected]/msg02548.html

Can someone give me a concrete example of why someone would want an _ in
a hostname in a cert? An all-Microsoft shop using it for an internal
name which nevertheless was an FQDN? my_server.corp.fooco.com?

_ is allowed at the DNS protocol level, so it works in many cases.  See the 
following (pulled from CT logs):

myaccount_ca.kelloggsnutrition.com
office_eygelshoven.laurametaal.nl
dr_mail.ncr.com

All of these have public A records with what appear to be public IPs.  Given 
this, they presumably work with many TLS clients.

Thanks,
Peter
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