Maintaining a Cache of Previously Queried

Prefixes “Telepathwords: Preventing weak passwords by reading

users’ minds.”

Saranga Komanduri, Richard Shay, Lorrie Faith Cranor, Cormac Herley, and Stuart Schechter.

In 23rd USENIX Security Symposium (USENIX Security 14). San Diego, CA: USENIX Association, pp. 591-606. 2014.

Presented by: Nazish Khan

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Summary

Requires efficient algorithms to model users’ behaviour and employ already-typed characters to predict subsequent ones

Real time predictions based on numerous predictors

Common character sequences

Keyboard movements

Repeated strings

Interleaved strings

Compared Telepathwords with composition rules

Feedback bar

Prediction display

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Storing Previous Queries

In an ideal situation, we would want no evidence of past requests

Authors take a security risk by maintaining a cache of previously queried prefixes on the server

Cache of past requests ---

Removal of past requests

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Issues

Why is it a security risk?

Cache becomes central point of storage (of previous queries- prone to attacks)

Is confidentiality guaranteed? No

Is integrity guaranteed? No

Protect the log but what about the cache?

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Securing the Log

Requests one-time session key

Generates session key, encrypt it with a public key andwrites encrypted session key to the log

Log

Sends the session key

XORs traffic with stream cipher and using symmetric encryption (AES)

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Justification

Authors hardly justify their decision to go ahead with this risk.

Why did they take this risk?

Reuse queries

Faster processing

Route all client-server communications over HTTPS

Server is unable to read the contents of the online log

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Conclusion

Cache is not protected

An attacker could gain access to the data

No confidentiality or integrity

When a user is typing text, no protection mechanism in memory.

Log has only been encrypted to cater for confidentiality

An attacker could modify its contents- threat to integrity

Thank you

Questions?

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My opinion

I have my doubts regarding the realistic use of this system

Need to give some crucial thought to the following questions:

Is security really important in such a system?

How to cater for the trade-off between security and usability? What’s more important? To whom?