[Cryptography] Langsec & authentication

[Judson Lester]

On Wed, May 28, 2014 at 10:29 PM, James A. Donald <jamesd at echeque.com> wrote:
> On 2014-05-28 05:30, Judson Lester wrote:
>>
>> But, and this is the other half of my dilemma, authenticating
>> ambiguous blobs of data opens a giant hole in your MAC system: here's
>> two documents that mean "re-order coffee" and "nuke North Korea" with
>> the same MAC. Oops. And while that's theoretically possible
>> regardless, it becomes much easier to do if there's many many ways to
>> say "nuke North Korea."
>
>
> Again, ASN.1 CANONICAL-PER

Myself, I'm a big fan of ASN.1, and especially of the canonical
encodings, but the langsec objection to PER and DER is that
length-prefix encodings are context-sensitive. My point in all this
has been: a full ASN.1 implementation includes sets, and attribute
lists, so that even without length-prefix (e.g. CER) I think full
ASN.1 would be context-sensitive - although some protocol definitions
might not be, and some set of protocol design constraints (e.g. "don't
use sets"), including using CER, might reduce the resulting protocol
language to regular.

Judson