Encryption Algorithm for Pagers

[jgrasty@pts.mot.com (Joey Grasty X3697 P6611)]

Hello, all:

I am looking for a simple encryption algorithm suitable for use
in pagers.  Ideally, the algorithm would need to have the following 
characteristics in order to be useful in pagers:

1.  key size no larger than 64 to 128 bits;
2.  decryption firmware 4k to 8k bytes in size for typical
    8-bit microcontrollers (e.g. 68HC05);
3.  decryption firmware able to run in near real-time with 
    bit rates to 2400 bps with microcontrollers running no 
    faster than 2 MHz;
4.  encryption algorithm should run in real-time on 68000
    class processors with capacity to support 8 2400 bps
    channels;
5.  EXPORTABLE <-- yeah, I know

First, a bit of basic information on how pagers and paging systems 
work.  This is a gross oversimplification, but it'll do for this 
discussion.  All protocols commonly used are all sent in the clear.

A paging terminal collects the page, converts the PIN number
into a pager capcode (address), encodes the message into the protocol
used by the pager and sends the page over a phone line to one or 
more transmitters that transmits the page at the appropriate time
(this depends on whether the protocol is synchronous or asynchronous).
The paging protocol consists of a sync word (fixed string of bits), a
capcode (address), and a message.  In an encrypted paging system, all
but the sync word would be encrypted.  Each pager would have a single
key for itself and a group key for group pages (pages that are sent
to a group of pagers -- each group has a group capcode).  The pager 
would decrypt each capcode and check to see if it matched that of the 
pager.  If so, the message would be decrypted and displayed.

The purpose of this request is to see if any existing encryption
algorithms would fit this requirement, and if so, the amount of effort
required to put this system into place.  It is very important that
the system be exportable.

Let me know your ideas; post to cypherpunks or e-mail as you wish.  If
the information above is not adequate to suggest an algorithm, let me
know and I can supply more information.

Regards,

Joey Grasty (jgrasty@pts.mot.com)
Staff Engineer
Asia Pacific Pager Development
Motorola Paging and Wireless Data Group
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