The RC5(R) Encryption Algorithm
                         General Information

                           RSA Laboratories
                        Revised April 7, 1995

This document copyright (C) 1995 RSA Laboratories, a division of RSA 
Data Security, Inc. License is granted to reproduce, copy, post, or 
distribute in any manner, provided this document is kept intact and 
no modifications, deletions, or additions are made.

RC5 is a registered trademark of RSA Data Security, Inc. Patent 
pending.


WHAT IS IT?

The RC5 encryption algorithm is a new fast symmetric block cipher 
developed by Ron Rivest for RSA Laboratories. Intended as a possible 
successor to the Data Encryption Standard, RC5 has a variable word 
size, a variable number of rounds, and a variable-length secret key, 
so the user can explicitly manipulate the trade-off between higher 
speed and higher security. RC5 is suitable for hardware or software 
implementations; the encryption and decryption algorithms are 
exceptionally simple. A novel feature of RC5 is the heavy use of 
data-dependent rotations.


HOW TO GET IT

To get a copy of Ron Rivest's paper describing the algorithm, send 
electronic mail to <rc5-paper@rsa.com>; a Postscript version will be 
returned. A LaTeX version is available via anonymous ftp to ftp.rsa.com 
in the pub/rc5 directory.

You can also get a copy of our reference implementation of RC5, but 
to do so you must be a U.S. or Canadian person, and you must return 
the following paragraph to <rc5-administrator@rsa.com>:

     I am hereby requesting a copy of the reference implementation of 
     the RC5 encryption algorithm for personal use and evaluation. I 
     acknowledge that no rights to copy, distribute, or sell the 
     Program are granted, and that such use of the Program is 
     prohibited. The electronic mail address to which I am requesting 
     that the reference implementation be transmitted is located in 
     the United States of America or Canada and I am a United States 
     citizen, a Canadian citizen, or a permanent resident of the 
     United States.


EVALUATION CONTEST

Through Summer 1995, we are encouraging people to evaluate the RC5 
algorithm, both for security and performance. In fact, we are 
offering prizes for the best papers on the security and performance 
of RC5. You don't have to break RC5 to win, just provide the most 
thorough and accurate analysis. For more information on the contest, 
send electronic mail to <rc5-prizes@rsa.com>.


LICENSES

After the evaluation period---and assuming RC5 holds up to 
scrutiny---RSA Laboratories will begin encouraging development of 
applications based on RC5, and granting license to the algorithm as 
well as the reference* implementation. At the present time, license 
is granted *only* for personal use and evaluation.

Our intent is that non-commercial use would be free, and commercial 
use would incur a fixed, one-time licensing fee to support continued 
research at RSA Laboratories.


USERS' GROUP

Developments on RC5 analysis and licensing will be posted to the 
<rc5-users@rsa.com> mailing list. To join, send electronic mail to 
<rc5-users-request@rsa.com>.


QUESTIONS?

If you have questions or comments about RC5, send electronic mail to 
<rc5-administrator@rsa.com>.


ABOUT RSA LABORATORIES

RSA Laboratories is the research and development division of RSA Data 
Security, Inc., the company founded by the inventors of the RSA 
public-key cryptosystem. RSA Laboratories reviews, designs and 
implements secure and efficient cryptosystems of all kinds. Its 
clients include government agencies, telecommunications companies, 
computer manufacturers, software developers, cable TV broadcasters, 
interactive video manufacturers, and satellite broadcast companies.

RSA Laboratories also offers Seminar Series covering technical 
background as well as the latest developments in cryptography, and 
Technical Reports exploring cryptography in depth.

RSA Laboratories draws upon the talents of the following people:

Len Adleman, distinguished associate - Ph.D., University of
  California, Berkeley; Henry Salvatori professor of computer 
  science at University of Southern California; co-inventor of
  RSA public-key cryptosystem; co-founder of RSA Data Security, Inc.

Taher Elgamal, senior associate - Ph.D., Stanford University;
  inventor of Elgamal public-key cryptosystem based on discrete 
  logarithms; holder of three patents for data compression algorithms 
  and implementations

Martin Hellman, distinguished associate - Ph.D., Stanford University;
  professor of electrical engineering at Stanford University; 
  co-inventor of public-key cryptography, exponential key exchange; 
  IEEE fellow; IEEE Centennial Medal recipient

Burt Kaliski, chief scientist - Ph.D., MIT; former visiting assistant
  professor at Rochester Institute of Technology;  editor of Public-Key 
  Cryptography Standards; general chair of CRYPTO '91; member, Internet 
  Privacy and Security Research Group; chair, IEEE P1363 working group

Cetin Koc, associate - Ph.D., University of California, Santa
  Barbara; assistant professor at Oregon State University

Ron Rivest, distinguished associate - Ph.D., Stanford University;
  professor of computer science at MIT; co-inventor of RSA public-key 
  cryptosystem; co-founder of RSA Data Security, Inc.; member of 
  National Academy of Engineering; director of International 
  Association for Cryptologic Research; program co-chair of ASIACRYPT 
  '91

Matt Robshaw, research scientist - Ph.D., University of London; member
  of EUROCRYPT '91 organizing committee

Yiqun Lisa Yin, research scientist - Ph.D., MIT

RSA Laboratories seeks the talents of other people as well. If you're 
interested, please write or call us.


ADDRESSES

RSA Laboratories
100 Marine Parkway, Suite 500
Redwood City, CA  94065 USA

(415) 595-7703
(415) 595-4126 (fax)
e-mail: rsa-labs@rsa.com