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Path: utzoo!mnetor!uunet!lll-winken!csustan!polyslo!caus-dp!marcos
From: marcos@caus-dp.UUCP (Marcos R. Della)
Newsgroups: comp.lang.pascal,sci.crypt
Subject: Implimenting this system...
Message-ID: <291@caus-dp.UUCP>
Date: Mon, 23-Nov-87 14:12:20 EST
Article-I.D.: caus-dp.291
Posted: Mon Nov 23 14:12:20 1987
Date-Received: Thu, 26-Nov-87 07:06:37 EST
Organization: USPFO for CA - Data Processing Div., SLO, Ca
Lines: 56
Keywords: Public Key systems
Xref: mnetor comp.lang.pascal:534 sci.crypt:729

+------------
| In article <283@caus-dp.UUCP> you ask...
|
| The basic theory they use is to convert your code to integer values
| below some value K where K is the product of two large primes (call them
| P and Q) There is one caveat on P and Q, neither (P - 1) or (Q - 1) can
| be divisible by three or the system will not work.
| 
| Now to encrypt, simply cube the cleartext message mod K, where K is
| regarded as the public encryption key.
| 
| To decrypt, evaluate the decryption key D such that
| 
| 	D = (2 * (P - 1) * (Q - 1) + 1] / 3
| 
| and decryption of a block B is simply (B ^ D) MOD K
| 
| i.e.
| 
| T: plaintext,	C: ciphertext
| 
| 	C = (T ^ 3) MOD K
| 	T = (C ^ D) MOD K
| 
| where K = P * Q (P and Q both primes w/ other caveats & restrictions)
| K is public key.
| and D = (2 * (P - 1) * (Q - 1) + 1] / 3
| D is private decryption key.
| 
| A couple of limitations on P and Q will make factorisation of K more
| difficult:
| 
| 	arrange P and Q so that both (P - 1) and (Q - 1) contain at least
| 		one large prime factor
| 	the ratio P / Q should not approximate a simple fraction (i.e.
| 		1/2, 2/3, 3/4, etc. etc. etc.)
| 
| 		dg@wrs.UUCP - David Goodenough
+----------

I have spent some time pouring through this description and have not yet
been able to produce anything that will work with it. My problem lies in
the section that says T = (C ^ D) MOD K. The problem I face is that D is
a large number and anything taken to a large number is rediculous in size.

Does someone have a fix that will make this a better system or maybe
another method that might not be as secure, but will still work on the
same principle of the encrypt and decrypt keys?

Any help would be appreciated...

Marcos R. Della
-- 
...!lll-crg -> !csustan -\                           | Whatever I said doesn't
            ...!sdsu ----->->!polyslo!caus-dp!marcos | mean diddly as I forgot
  ...!ihnp4 -> !csun ----/                           | it even before finishing
            ...!dmsd ---/                            | typing it all out!!!