说明：  RC5 block cipher. This implementation is FREEWARE, you may use this implementation freely. You have permission to modify any of the files included in this archive provided you do not redistribute these files. If you wish to redistribute these implementations you may do so provided all the files in this archive are kept intact and unmodified. If you do redistribute these files please email me and tell me (if you upload to a BBS/web site/ftp site etc), this is not a requirement but it is nice to know who is using these implementations.