[TLS] about the PWD Proposal

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Hi,
 I am interested in the PWD proposal at the meeting, and run through 
it(http://tools.ietf.org/html/draft-harkins-tls-pwd-01#section-3.4),
 and have the following concerns:

1. In the document, it  says both Client and Server should be able to 
compute PE, which is derived from username, password, salt,etc.
   That means Client or the user should also remember the salt value, in 
that case, salt is meaningless and can be replaced by a longer password.
   This is quite different from the widely known usage of salt, e.g. in 
UNIX operating system, salt is not required to remember by the user, but 
by server to fetch locally by reference to the username. 
  And as far as I know, I am sure the authors also know that, other 
password based key exchanges protocols don't involve salt, but store a 
hash value of password among other things locally.
2. From the figure in the PPT shown at the meeting, I cann't see why the 
protocol should use both "private" and "mask" values, in my opinion, only 
"mask " value shall be OK.
   private value is redundent, and not helpful in security improvement.
   because the current derived shared key is PE^{private_a*private_b} 
according to this document， and
   after removing private value, it will be  PE^{mask_a*mask_b}
   and private, mask value are both generated locally and not transported 
on the wire, so it does not make much difference except making it more 
complex.
3. Now I only talk about the security of the simplified version (as in 
above point 2)
   after simplification the protocol is easier to analysize, it is just 
like an ordinary DH exchange except that the base group generator is PE 
instead of g.
   So the security is reduced to the PE, is it a good group generator 
which has large order? if not then it is insecure.
   Unfortunatly the authors failed to analysize this crucial point.

Thank you for your patience!

Sujing Zhou 
 


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