Communications of the ACM
Securing Network Time Protocol
In the late 1970s David L. Mills began working on the problem of synchronizing time on networked computers, and Network Time Protocol (NTP) version 1 made its debut in 1980. This was when the Net was a much friendlier place—the ARPANET days. NTP version 2 appeared approximately one year later, about the same time as Computer Science Network (CSNET). National Science Foundation Network (NSFNET) launched in 1986. NTP version 3 showed up in 1993.
Depending on where you draw the line, the Internet became useful in 1991–1992 and fully arrived in 1995. NTP version 4 appeared in 1997. Now, 18 years later, the Internet Engineering Task Force (IETF) is almost done finalizing the NTP version 4 standard, and some of us are starting to think about NTP version 5.