[Security] About the Firefox 3 Security Dialog & others

Pedro Melo melo at simplicidade.org
Fri Aug 22 17:12:55 CDT 2008


Hi again,

On Aug 22, 2008, at 10:58 PM, Pedro Melo wrote:
> On Aug 22, 2008, at 9:16 PM, Jonathan Schleifer wrote:
>
>> Am 22.08.2008 um 22:00 schrieb Pedro Melo:
>>
>>> SAS, I meant SAS.
>>
>> Just to be sure: What's the exact difference between SRP and SAS?  
>> I only had a short look at SRP and it seemed pretty similar.
>
> The references I found:
>
>  * SAS: http://www.ietf.org/internet-drafts/draft-barreto-ietf- 
> dhhmac-sas-00.txt;

A better reference for SAS, given our context of TLS, is this:

https://svn.resiprocate.org/rep/ietf-drafts/ekr/draft-mcgrew-tls-sas.txt

After doing the protocol you end up with a (minimal) 20bit SAS string.

They recommend (section 5.2.1 Representing the SAS) that we use a  
base32 representation. I personally prefer to use the mnemonic  
encoder (http://tothink.com/mnemonic/) that gives me a set of three  
pronounceable and distant words.

Anyway, I prefer SAS because it simpler than SRP, given that I  
usually have an alternative channel (not necessary a secure one). SRP  
usually requires physical contact to exchange the secret, and if I'm  
with the person I want to authenticate, I might as well compare the  
full signature...

Best regards,


>  * SRP: http://srp.stanford.edu/whatisit.html
>
> If there are better ones, I would appreciate the links.
>
> In the SAS case, it seems that you basically have a 32 bit  
> signature to send over an alternative channel. Each person reads  
> that 32bit signature to each other and if they match, the key is  
> trusted. Please correct me if I'm wrong.
>
> What I like in SAS is that the 32bit key can be coded with words  
> using something like this: http://tothink.com/mnemonic/
>
> This generates three words that encode the 32bit number. You can  
> check the URL but the choice of the word list was the interesting  
> factor for me. It gives you words that are pretty distant from each  
> other and over a voice channel less likely to be misinterpreted.
>
> Best regards,
> -- 
> Pedro Melo
> Blog: http://www.simplicidade.org/notes/
> XMPP ID: melo at simplicidade.org
> Use XMPP!
>
>

-- 
Pedro Melo
Blog: http://www.simplicidade.org/notes/
XMPP ID: melo at simplicidade.org
Use XMPP!




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