RE: pre-shared key v RSA encryption or RSA signature authentication modes

[Michael Choung Shieh <mshieh@netscreen.com>]

I don't think the protocol itself has the limitation on the length of
preshare key. so the answer shouldn't be RSA-sig is stronger, but preshare
key could allow users to use weaker entropy.

Michael

> -----Original Message-----
> From: Derek Atkins [mailto:warlord@mit.edu]
> Sent: Thursday, March 21, 2002 8:40 AM
> To: Uri Blumenthal
> Cc: Prof. Ahmed A. A. Adas; cdemar@ebsdr.com; ipsec@lists.tislabs.com
> Subject: Re: pre-shared key v RSA encryption or RSA signature
> authentication modes
> 
> 
> The fact that most users wont have a shared secret with 256 bits of
> entropy?  I suspect that most shared secrets are probably in the 64-80
> bits of entropy at the highest, and probably much lower than that.
> 
> Based on the lack of entropy in shared secrets, I believe RSA sigs
> to be much stronger due to the better entropy in the key.
> 
> -derek
> 
> Uri Blumenthal <uri@lucent.com> writes:
> 
> > "Prof. Ahmed A. A. Adas" wrote:
> > > As a researcher in cryptosystems and protocols, I would 
> say that RSA-sig IKE
> > > is much more powerful unless someone is using quantum 
> computing attacks,
> > > which are not feasible in the near future.
> > 
> > It is comparing apples with oranges.  The conclusion appears
> > incorrect,
> > and way too generalizing [without due justification].
> > 
> > Please explain - based on what is, say 2048-bit RSA-sig 
> stronger than,
> > say 256-bit key-based AES-XCBC-MAC signature? What is your criteria?
> > What attacks are you considering? What is your model?
> > --
> > Regards,
> > Uri
> > -=-=-=<>=-=-
> > <Disclaimer>
> 
> -- 
>        Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
>        Member, MIT Student Information Processing Board  (SIPB)
>        URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
>        warlord@MIT.EDU                        PGP key available
>