un-trusting MD5 in gpg

David Shaw dshaw at jabberwocky.com
Wed May 6 22:23:19 CEST 2009

On May 6, 2009, at 4:04 PM, Daniel Kahn Gillmor wrote:

> On 05/06/2009 03:42 PM, David Shaw wrote:
>> I like this basic idea (though don't like the name "weak" for  
>> reasons I
>> mentioned earlier).  The analogy to personal-digest-preferences is a
>> good one: this is the personal-digest-anti-preferences.  Instead of  
>> the
>> algorithms the user likes and wants to use when possible, these are  
>> the
>> algorithms the user dislikes and won't accept.
> --unacceptable-digest-algos maybe?  Your point about "weak" is a good
> one, i think.  i was unaware that WEAK_KEY had a specific technical  
> meaning.

Maybe we should name it personal-digest-something.  It makes it clear  
that these are personal settings, pertain to digests, and that this is  
sort of a parallel function to personal-digest-preferences.  What are  
the antonyms of preferences?  personal-digest-dislikes?  personal- 
digest-rejections?  personal-digest-disable?

>   Having the two
> options allows for some weird (and unnecessary) configurations, like:
> --unacceptable-digest-algos MD5 --personal-digest-preferences MD5
> wherein you would only make signatures that you would never believe  
> were
> valid.  The answer of course, is Don't Do This, but it's unfortunate  
> to
> give the user that much rope.

Hashes are a bit easier, but you can imagine some real problems with a  
list of unacceptable ciphers.  Let's say that we had a user who set  
"personal-cipher-donotaccept 3des".  What could this user do when  
encrypting to a bunch of recipients whose ciphers do not intersect on  
anything other than 3des? I guess the best thing to do would be to  
simply error out.


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