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The Pure Crypto Project's Hash Function

daemon@ATHENA.MIT.EDU (Ralf Senderek)
Fri May 2 21:26:37 2003

X-Original-To: cryptography@metzdowd.com
X-Original-To: cryptography@metzdowd.com
Date: Fri, 2 May 2003 19:42:04 +0200 (CEST)
From: Ralf Senderek <ralf@senderek.de>
To: <cryptography@metzdowd.com>

I would like to ask the list's expertise to assess the
hash function below, which is used in the Pure Crypto Project
to create signatures. The project's intention is to provide
encryption and signing with the smallest amount of readable
code possible using only one basic crypto primitive,
a function ModExp(A,B,C) which calculates A**B mod C.

As this function is neccessary for RSA encryption the hash
function should be based on this function as well, even though
that slows down the process. You can find my remarks on the
security of the hash function at:


I would be very thankful for comments and constructive criticism.

The Pure Crypto Hash Function :

    Prime = 106603488380168454820927220360012878679207958575989291522270608

    Ho = PublicKeyModulus mod Prime

    for every character in the message text
         Hi+1 = (Hi + 19) XOR ModExp((Hi + Ho), (character i + 19), Prime)

The hash function produces 256 bit output values.

Thanks in advance.

    Ralf Senderek

* Ralf Senderek  <ralf@senderek.de> http://senderek.de  * What is privacy *
* Sandstr. 60   D-41849 Wassenberg  +49 2432-3960       *     without     *
* PGP: AB 2C 85 AB DB D3 10 E7  CD A4 F8 AC 52 FC A9 ED *   Pure Crypto?  *

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