sbin/md5/md5-announcement.txt

                 MD5 -- New Message Digest Algorithm
                  (Feel free to distribute further)

RSA Data Security is announcing MD5, a new message-digest algorithm.
Like MD4, this algorithm is being placed in the public domain for free
general use.

The MD5 algorithm is a strengthened version of MD4.  It has four
rounds instead of three, and incorporates other revisions based on a
year's worth of collected comments on the MD4 algorithm.  For example,
the input access patterns in rounds two and three have been improved,
and the rotation amounts have been optimized for maximum ``avalanche
effect.''  The additive constants have been made unique in each step,
and an additional dependence of each step on the previous one has been
added.

These changes cause MD5 to be somewhat slower than MD4.  We estimate
that MD5 will typically run about 15-30% slower than MD4, depending on
the degree to which the versions of MD4 and MD5 have been optimized.
The more they are both optimized, the greater the percentage
difference in speed.  An optimized version of MD5 on a Sun
SparcStation runs at about 890 Kbytes/second.

Why MD5?  While we do not know of any way to ``break'' MD4, we feel
that MD4 is being pressed into service far too quickly for such an
``aggressive'' design.  We have been surprised at the speed with which
MD4 is being designed into products.  MD5 is ``MD4 with seatbelts''
and thus, as a more conservative design, is more suitable for rapid
deployment.

It is the intent of RSA Data Security to use MD5 in its products and
standards instead of MD4.  We recommend that our customers generally
do the same, unless there is an overwhelming need for the higher speed
of MD4.  Copies of the MD5 algorithm, including a reference
implementation in C, are available from the company.  (Over the
Internet, you can access this documentation by anonymous FTP to
rsa.com and obtaining the file pub/md5.doc.)