Internet Engineering Task Force Proposes Standard for Network Time Security

IETF Publishes New Proposal to Add Security to Network Timing

The Internet Engineering Task Force (IETF) has published RFC8915, its proposed standard for network time security (NTS). It has been five years in the making and is designed to remedy the issues and vulnerabilities that exist in the current network time protocol (NTP).

Accurately synchronized time between different computers over packet-switched, variable-latency data networks is essential. This becomes even more critical in the age of the fourth industrial revolution, where the accurate timing and sequence of different processes is vital. Since its launch in 1985, NTP has served this purpose well. However, over the last 35 years it has become apparent that various vulnerabilities and issues in NTP demonstrate that it requires an increased level of security. NTS is designed to provide that security.

The existing issues affecting basic NTP include DDoS amplification, packet manipulation, and replay attacks — the last two being implemented by man-in-the-middle (MiTM) attacks that can forge messages and falsify the time.

The primary solution has been the introduction of asymmetric cryptography to the initial server authentication. This can prevent MiTM attacks. That it operates slower than symmetric encryption opens an increased possibility of DDoS attacks against NTP servers. However, as RFC8915 notes, “a successful DDoS attack on an NTS-KE server separated from the NTP service it supports will not affect NTP users that have already performed initial authentication, AEAD key extraction, and cookie exchange.”

The proposed standard also warns that NTS does not fully protect against attacks from on-path adversaries. “In addition to dropping packets and attacks… an on-path attacker can send spoofed Kiss-o’-Death replies, which are not authenticated, in response to NTP requests.”

However, NTS does largely prevent the use of some NTP implementations in DDoS amplification attacks. “Certain nonstandard and/or deprecated features of the Network Time Protocol enable clients to send a request to a server that causes the server to send a response much larger than the request,” notes the standard. NTS avoids contributing to this problem by ensuring that NTS-related extension fields included in server responses are the same size as the fields sent by the client.

This is not a hundred-percent accurate statement since RFC7822 requires that extensions be padded and aligned to four-octet boundaries — meaning that response size may in some cases exceed request by up to three octets. But as the IETF comments, “This is sufficiently inconsequential that we have declined to address it.”

“The publication of RFC8915 is an important moment both for the development of NTS and for security on the Internet in general,” comments Lars Michael Jogback, the CEO of Netnod. Netnod is a Swedish firm that provides NTP, NTS and Precision Time Protocol (PTP) services. “Netnod is proud to have been at the forefront of developing the NTS standard and implementations. We will continue to focus on services such as NTS to make the Internet as secure and robust as possible for everyone.”

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