Re: [secdir] Please review draft-ietf-capwap-protocol-specification's use of certificates

["Scott G. Kelly" <s.kelly@xxxxxxxxxxxxx>]

Hi Steve,

Thanks for taking a look at this. Regarding placement of the MAC in the CN, I would offer two observations: 

1) this is what is specified in the DOCSIS and PacketCable cert profiles, and it was on this basis that device certs for LWAPP were originally designed in this way. You can see the DOCSIS profile at www.drizzle.com/~aboba/CPW/DOCSIS.ppt

2) I don't see anything in the X.520 language that explicitly precludes this usage, so assuming that the docsis/packetcable designers reviewed that spec, I can see how they could reasonably conclude that this is acceptable. Arguably, the string representation of the MAC address is "a string chosen [by the] organization responsible for the object it describes for devices and application entities". 

Please don't misunderstand: I'm not trying to be difficult, and I have a very healthy respect for the depth of your knowledge in this area. However, there are a *lot* of devices deployed that already use this convention. It might be more pragmatic to interpret X.520 a little less restrictively.

Scott

-----Original Message-----
>From: Stephen Kent <kent@xxxxxxx>
>Sent: Dec 21, 2007 3:00 PM
>To: Sam Hartman <hartmans-ietf@xxxxxxx>
>Cc: capwap-chairs@xxxxxxxxxxxxxx, ietf-pkix@xxxxxxx, secdir@xxxxxxx
>Subject: Re: [secdir] Please review draft-ietf-capwap-protocol-specification's use of certificates
>
>At 9:23 PM -0500 12/20/07, Sam Hartman wrote:
>>Hi, folks.  The capwap working group is preparing to last call their
>>protocol specification draft.
>>
>>I'd appreciate review from the pkix community of section 2.4.4.3 and
>>12.6 of this draft.  These sections specify certificate validation and
>>certificate usage for the protocol.  Scott Kelly and Charles Clancy
>>are security advisors for the working group and have been heavily
>>involved.
>>
>>The capwap certificate profile assumes that the CN in the certificate
>>has structure and contains an ethernet MAC address.  The capwap
>>certificate profile also assumes that parts of the subject name such
>>as the organization and organizational unit will be important to
>>certificate matching.
>>
>>I'd appreciate review and comments.
>>
>>--Sam
>
>It would be preferable to get an allocated name space for MAC 
>addresses, under the OtherName or, better yet, under registeredID.
>
>I'd argue that it is inappropriate to put a MAC address into a CN. 
>The text from X.520 makes this clear:
>
>The Common Name attribute type specifies an identifier of an object. 
>A Common Name is not a directory name; it is a (possibly ambiguous) 
>name by which the object is commonly known in some limited scope 
>(such as an organization) and
>conforms to the naming conventions of the country or culture with 
>which it is associated.
>
>An attribute value for common name is a string chosen either by the 
>person or organization it describes or the organization responsible 
>for the object it describes for devices and application entities. For 
>example, a typical name of a
>person in an English-speaking country comprises a personal title 
>(e.g., Mr., Ms., Rd, Professor, Sir, Lord), a first name, middle 
>name(s), last name, generation qualifier (if any, e.g., Jr.) and 
>decorations and awards (if any e.g., QC).
>
>Examples
>CN = "Mr. Robin Lachlan McLeod BSc(Hons) CEng MIEE"
>CN = "Divisional Coordination Committee"
>CN = "High Speed Modem".
>
>If there is a very strong desire to make use of an existing attribute 
>in the X.502 space, the SerialNumber attribute makes more sense. So 
>long as we are talking about long, term, stable MAC addresses 
>assigned to devices by manufacturers, this is consistent with the 
>semantics of that attribute.  Moreover, we have advised folks to use 
>SerialNumber to represent data such as employee/student IDs in the 
>past, so one might expect to see support for this attribute in many 
>CAs and clients.
>
>Steve