1. Timing Analysis of Keystrokes And Timing Attacks on SSH
Authers:dawn xiaodong song,david wagner xuqing tian publication:usenix security simposium presenter: hiral chhaya for cap 6133

2. Outline…… Secure Shell (SSH) weaknesses
Analysis of user keystroke patterns
Attack using inter-keystroke timing
Performance evaluation
Countermeasures
Comments and conclusion

3. Ssh- secured shell
Offers an encrypted channel and strong authentication.
Replaces telnet, rlogin.
protects a network from attacks such as IP spoofing, IP source routing, and DNS spoofing.
If attacker tries to takeover the network SSh diconnects.

4. Ssh- secured shell

5. Weeknesses of ssh Two seemingly minor weaknesses: Padding: 1-8 bytes
Reveals approximate data size
In interactive mode, every individual keystrokes is sent to remote machine in separate IP packet.
Leaks timing information of user’s typing
Padding length
Random Padding
Payload
Integrity data (MAC)
Packet
length

6. Traffic signature attack

7. Traffic signature attack

8. Traffic signature attack

9. Traffic signature attack

10. Traffic signature attack

11. Traffic signature attack

12. Traffic signature attack

13. Traffic signature attack

14. Traffic signature attack

15. Traffic signature attack

16. Traffic signature attack

17. Traffic signature attack

18. Traffic signature attack

19. Traffic signature attack

20. Nested ssh attack User establish SSH session between A and B
Another session from B to C
User’s password for C is transmitted across ssh link A-> B
Adversary sniff the password

21. Statistical analysis of inter-keystroke timings
Pick a pair of characters, e.g. (“v”, “o”)
Ask users to type the pair for times
Collect latency information
Repeat for every different pair of characters

25. Hidden markov model (hmm)
HMM - A Markov model when the current state can not be observed.
Outputs of the process are observed.
Probability of output depends only on the state.
Information on the prior path of the process can be inferred from it’s output.

26. Hidden markov model (hmm)
Character pair is the hidden state.
Keystroke latency measured is the output observation.
Two assumptions:
Probability of transformation from current state to another state, depends only on the current state.
Probability distribution of latency, depends only on the current state
q = character pair
y = latency observation

27. Big picture Detect SSH session detect nested SSH or SUA B
Sniffer
detect nested SSH
or SU
Keystroke Timing
statistics
n-Viterbi
Possibilities
Password

28. countermeasures
Let the server return dummy packets when it receives keystroke packets from the client.
Let the client randomly delay sending keystroke packets.
Let the client send keystroke packets at a constant rate.

29. strengths Novel idea Nice technique Good performance
Interesting findings
Countermeasures given

30. weeknesses No mention of how to deal with backspace
No discussion of how different keyboard layouts affect the results
Laptop vs desktop
Different keyboard layouts in different regions

31. THANK YOU