I am doing some research in order to get an understanding of the security of the Network Time Protocol. In particular, my goal was/is to understand how the protocol is secured and what the issues are.
So far, I understood that there are basically 2 ways to secure NTP, in order to provide authentication (and integrity as well, since a MAC is used): via symmetric cryptography and via public key cryptography. However, for several reasons (that I do not list explicitly for the sake of space), these 2 measurements are often not used and therefore NTP is left unauthenticated. This leads to a series of issues in terms of security.
My question is: in practice, how often is NTP really subject to attack? I know that there is the possibility of both on-path and off-path attacks, and that some of them have been fixed (I mainly refer to the studies done by the Boston University research group). If it was so easy to hack a protocol like NTP, everyone would be messing up with applications relying on time (certificates etc.). From what I read, in general, it seems like in fact there are not so many attacks available on NTP, although most of the times the protocol is not secured. The only exception seems to be DDoS attacks (such as amplification and reflection attacks), for which there are not so many solutions. Did I get this right or am I missing something important from the big picture?
Another question: why only recently some new solutions have been proposed? I am referring mainly to the Network Time Security specification (pdf) to secure NTP, which was also presented at Real World Cryptography Conference 2017 by one of the authors of the IETF draft (Daniel Franke). What I have been wondering is whether this solution would really provide something useful, since people keep using NTP without authentication and they do not seem to worry too much about it.
I hope my question was clear.