This memorandum describes extensions to the Network Time Protocol (NTP) version 3, described in RFC 1305 [MIL92], and the Simple Network Time Protocol (SNTP) version 4, described in RFC 2030 [MIL96a], to create a framework for interoperability and coexistence of various cryptographic signature and authentication schemes that have been suggested as enhancements to NTP/SNTP [MIL96b]. Without desc...