Malicious Cryptography: Exposing Cryptovirology

Chapter 6

Computationally Secure Information Stealing

Perhaps the two biggest fears that the victim of a computer virus has is that information has been covertly stolen or that data files have been deleted or altered by the virus. This chapter focuses exclusively on the former fear. Such viruses are among the most insidious since they can steal information for an indefinite period of time before ever being noticed.

More specifically, the problem of designing malware to securely and privately steal information is considered. The chapter begins with a straightforward cryptovirological approach that utilizes the public key of the malware author. However, this approach has a significant drawback since the virus code reveals the data that it is trying to steal. This drawback forms the motivation for a stronger model to privately obtain information. This strong model is known as the private information retrieval (PIR) problem. The notion of a PIR scheme is given and various approaches to solving this problem are mentioned.

A computationally secure PIR scheme is then described that has some very desirable properties from an operational standpoint. A few variants of this scheme are presented, thereby developing a heuristic solution that is amenable for use in real-world malware. Such malware is capable of privately stealing information without revealing anything about the information that ...