http://cpansearch.perl.org/src/NWINT/MD5-1.7/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.
*
**********************************************************************