http://www.rfc-editor.org/rfc/rfc4757.txt
RFC 4757: The RC4-HMAC Kerberos Encryption Types Used by Microsoft Windows, K. Jaganathan, L. Zhu, J. Brezak2006-12-01T23:00:00-00:00The RC4-HMAC encryption types are used to ease upgrade of existing Windows NT environments, provide strong cryptography (128-bit key lengths), and provide exportable (meet United States government export restriction requirements) encryption. This document describes the implementation of those encryption types. This memo provides information for the Internet community.