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RC5 Background Information
Here is a short section from the informational RFC on
the RC5 cipher. It seems to answer many of the questions we have
seen posted to the list.
--Bob
1. Executive Summary
This document defines three ciphers with enough detail to ensure
interoperability between different implementations. The first cipher is
the raw RC5 block cipher. The RC5 cipher takes a fixed size input block
and produces a fixed sized output block using a transformation that depends
on a key. The second cipher, RC5-CBC, is the Cipher Block Chaining (CBC)
mode for RC5. It can process messages whose length is a multiple of the
RC5 block size. The third cipher, RC5-CBC-Pad, includes padding in the CBC
mode to allow it to process inputs of any byte length.
The RC5 cipher was invented by Professor Ronald L. Rivest of the
Massachusetts Institute of Technology in 1994. It is a very fast and
simple algorithm that is parameterized by the block size, the number of
rounds, and key length. These parameters can be adjusted to meet different
goals for security, performance, and exportability.
A patent application has been filed for the RC5 cipher. The terms RC5,
RC5-CBC, RC5-CBC-Pad and assorted variations on these are trademarks.
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