From: Robbie Gates <gates_r@maths.su.oz.au>
Date: Tue, 5 Dec 95 16:03:36 PST
To: solman@MIT.EDU
Subject: Re: Secure versus ?
In-Reply-To: <9512051652.AA17214@ua.MIT.EDU>
Message-ID: <30C4DED5.15FB@maths.su.oz.au>
MIME-Version: 1.0
Content-Type: text/plain


solman@MIT.EDU wrote:
> Alice wants to use the inner loop to send bit b.
> 1. Alice randomly chooses seven bits of salt, and prepends b to them
>    creating an 8 bit M
> 2. Alice randomly chooses an (Na,Ea) pair from the list of possibilities.
> 3. Alice calculates D such that E*D mod (N-1) equals 1
> 4. Bob randomly chooses an (Nb,Eb) pair from the list of possibilities.
> 5. Bob calculates D
> 6. Alice sends Bob the nine bit number (M^Ea) mod Na = C1
> 7. Bob sends Alice (C1^Eb) mod Nb = C2
> 8. Alice sends Bob (C2^Da) mod Na = C3
> 9. Bob calculates (C3^Db) mod Nb = M, the bit being the MSB.

i don't think the maths works here ... let
Na = 257, Ea = 13, Da = 197, Nb = 263, 
Eb = 11, Db = 143

choosing M = 2, i calculate
C1 = 225, C2 = 144, C3 = 205, C4 = 33 != M
(and bottom bit is different)
choosing M = 7, i get
C1 = 127, C2 = 53, C3 = 19, C4 = 139 != M
(and top bit is different)

so your channel doesn't get the bit from alice to bob ...

the problem is that you are mixing reduction modulo two different numbers
Na and Nb ... this screws up the powering law you are trying to use.

 - robbie
-- 
----------------------------------------------------------------------
      robbie gates      | it's not a religion, it's just a technique.
  apprentice algebraist |    it's just a way of making you speak.
    pgp key available   |       - "destination", the church.