[cryptography] preventing protocol failings

Peter Gutmann pgut001 at cs.auckland.ac.nz
Wed Jul 6 02:25:09 EDT 2011


Nico Williams <nico at cryptonector.com> writes:
>On Wed, Jul 6, 2011 at 12:06 AM, Peter Gutmann
><pgut001 at cs.auckland.ac.nz> wrote:
>> (The ASN.1 filter I mentioned earlier is a stripped-down version of dumpasn1.
>> Remember that dataset of 400K broken certs that NISCC generated a few years
>> ago and that broke quite a number of ASN.1-using apps (and filesystems when
>> you untarred it :-)?  It processed all of those without any problems).
>
>Do you have a link for that dataset?  

You have to write to them and they'll send you a CD.  I'm not sure if it's 
available online anywhere.

>I want to check if the data is for explicitly or implicitly tagged modules.

It's randomly-modified cert data, there's every kind of tagging in there, 
including ones you've never heard of before (due to the random permutations 
used).

>See "ASN.1 Communication Between Heterogeneous Systems", page 213, which says 
>that "[a] type tagged in implicit mode can be decoded only if the receiving 
>application 'knows' the abstract syntax, that is, the decoded has been 
>generated from the same ASN.1 module as the encoded was".  

I know what implicit and explicit tagging is.  You don't need to know the 
syntax at all, a few simple heuristics will get BIT STRING and OCTET STRING 
holes and the like.  Throw stuff at dumpasn1 and see what it gives you.

Peter.



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