Summary

The SSH protocol uses openly published, strong cryptographic tools to provide network connections with privacy, integrity, and mutual authentication. The SSH-1 protocol (a.k.a SSH-1.5) is wildly popular, despite being somewhat ad hoc: essentially a documentation of SSH1's program behavior. It has a number of shortcomings and flaws, of which the weak integrity check and resulting Futoransky/Kargieman insertion attack is perhaps the most egregious example. The current protocol version, SSH-2, is more practically flexible and fixes the known earlier problems but has unfortunately seen limited deployment due to licensing restrictions and the continued availability of the free SSH1 software for many commercial purposes.SSH counters many network-related security threats, but not all. In particular, it is vulnerable to denial-of-service attacks based on weaknesses in TCP/IP, its underlying transport. It also doesn't address some methods of attack that may be of concern depending on the environment, such as traffic analysis and covert channels.