[security] Diffie-Hellman parameter validation

[Johnny Bufu]

Jason Fritcher pointed out in a thread on the openid4java list that  
there may be a security issue with the way the DH session is  
established:

> I've been thinking about how the RP can supply DH parameters to the
> OP, and was wondering if any discussion has occurred about whether to
> include language in the spec about how OPs should do validation of the
> DH params that get sent to them. A few quick checks of the modulus
> like primality checking and possibly enforcing the use of safe primes.
> It might also be good to check the supplied generator to make sure it
> is valid for the supplied modulus. I'm no where close to being being a
> crypto guru, but I wrote a Secure Remote Password implementation and
> after the research I did for that, not checking the DH params in the
> OP seems like a weakness. I might just be overly paranoid here and
> OpenID really doesn't need that level of security, but I thought I'd
> ask.

<http://groups.google.com/group/openid4java/browse_thread/thread/ 
f96a7b68bb15272d/c9f0f1a85e3372cc#c9f0f1a85e3372cc>

I am not a security expert either, but this seems a valid point to  
me. Can someone with deeper crypto knowledge please confirm / infirm?


I think we should either mention that the OP SHUOLD perform such  
validation, or at least mention the possible eavesdropping attack in  
the security considerations section.


Thanks,
Johnny