From: linn@albeit.enet.dec.com (John Linn. LKG1-2/A19. {-486 or DTN 226}-7384.  07-Oct-1992 1359, 508)
Subject: Re: Kerberos DES <> MD5
Organization: Internet-USENET Gateway at Stanford University
Date: Wed, 7 Oct 1992 17:56:50 GMT

>In article <1992Oct7.112104.13517@nic.funet.fi> netmgr@tellus.csc.FI (Pekka  
>Kytolaakso) writes:
>> Are there any plans to make Kerberos V5 also use MD5 and not just DES.
>> If i understand right MD5 has no export restrictions like DES.  Then you
>> could make a kerberos_export.tar.Z that has the DES-part stripped out.
>> 
>> And example authentication library using MD5 and DES is in the
>> latest version of xntp: ftp@louie.udel.edu:/pub/ntp/xntp3.tar.Z and
>> ..../xntp3.export.tar.Z.
>> 
>> Pekka Kyt|laakso
>> --
>> ---------------------------------------------------------------
>> netmgr@tellus.csc.fi     Centre for Scientific Computing
>> Pekka.Kytolaakso@csc.fi  PL 40   SF-02101 Espoo FINLAND
>> Phone: +358 0 4571       Telefax: + 358 0 4572302
>
>I believe that MD5 is patented by RSADSI in the US of A.  It may be used
>only under license from RSADSI in this country.  Due to the differences of
>US vs. other countries' patent laws, RSADSI does not hold patents for
>these same algorithms in most other countries of the world.  This has something
>to do with the order in which the paper describing the algorithm and the
>patent application are dated.  I believe the paper was published first, which
>makes it unpatentable in many countries except the US.  So you can use it
>for free in Finland but we can't here.  So instead of an export restriction
>barrier, you hit a patent barrier.  Besides, any crypto technology is  
>restricted from export.  So, an export license would be necessary for RSA
>just as it is for DES and a Captain Midnite Decoder Ring.
>/a

I think there may be some confusion here between MD5 (a message digest
algorithm, available in RFC-1321) and the RSA public-key cryptographic
algorithm.  Excerpting from RFC-1321:

>The MD5 algorithm is being placed in the public domain
>   for review and possible adoption as a standard.

[...]

>/* MD5.H - header file for MD5C.C
> */
>
>/* Copyright (C) 1991-2, RSA Data Security, Inc. Created 1991. All
>rights reserved.
>
>License to copy and use this software is granted provided that it
>is identified as the "RSA Data Security, Inc. MD5 Message-Digest
>Algorithm" in all material mentioning or referencing this software
>or this function.
>
>License is also granted to make and use derivative works provided
>that such works are identified as "derived from the RSA Data
>Security, Inc. MD5 Message-Digest Algorithm" in all material
>mentioning or referencing the derived work.
>
>RSA Data Security, Inc. makes no representations concerning either
>the merchantability of this software or the suitability of this
>software for any particular purpose. It is provided "as is"
>without express or implied warranty of any kind.
>
>These notices must be retained in any copies of any part of this
>documentation and/or software.
> */

Proper identification of the MD5 algorithm shouldn't constitute a prohibitively
onerous barrier to its use. Responding to the initial question, though, MD5
(since it's a message digest, not an encryption function) wouldn't be a
replacement for DES (which is an encryption function).  Taking a strong
authentication  mechanism based on the combination of MD5 and DES and simply
removing the DES wouldn't be likely to yield another strong authentication
mechanism as a result. There are, however, examples (e.g., SNMP security) of
use of MD5 with a secret seed as the basis for an authentication mechanism.

--jl