Kleptography

Kleptography is the study of stealing information securely and subliminally. Kleptography is a natural extension of the theory of subliminal channels. [ [http://www.cryptovirology.com/cryptovfiles/cryptovirologyfaqver1.html Cryptovirology FAQ ] ]

Kleptography was introduced by Adam Young and Moti Yung in the Proceedings of Advances in Cryptology---Crypto '96. A kleptographic attack is a forward-engineering attack that is built into acryptosystem or cryptographic protocol. The attack constitutes an "asymmetric backdoor"that is built into a smartcard, dynamically linked library, computer program, etc.The attacker that plants the backdoor has the exclusive ability to use the backdoor. In otherwords, even if the full specification of the backdoor is published, only the attacker can use it.Furthermore, the outputs of the infected cryptosystem are computationally indistinguishablefrom the outputs of the corresponding uninfected cryptosystem. So, in black-boximplementations (e.g., smartcards) the attack may go entirely unnoticed. The asymmetryensures that a well-funded reverse-engineer can at most detect the asymmetric backdoor butnot use it.

In contrast, a traditional, more common backdoor is called a "symmetric backdoor". Anyone that finds the symmetric backdoor can in turn use it.

Kleptographic attacks have been designed for RSA key generation, the Diffie-Hellmankey exchange, the Digital Signature Algorithm, and other cryptographic algorithms andprotocols.Fact|date=May 2008 The attacker is able to compromise said cryptographic algorithms and protocolsby inspecting the information (if available) that the backdoor information is encodedin (e.g., the public key, the digital signature, the key exchange messages, etc.) and then exploiting the logic of the asymmetric backdoor using his or her secret key (usually a private key).

Kleptography is a subfield of Cryptovirology since an asymmetricbackdoor is a form of cryptotrojan. Related fields include Cryptologyand Steganology. Kleptography extends the theory of subliminal channels that was pioneered by Gus Simmons [Si84,Si85,Si93] .

Footnotes

References

[Si84] G. J. Simmons, "The Prisoners' Problem and the Subliminal Channel," InProceedings of Crypto '83, D. Chaum (Ed.), pages 51-67, Plenum Press, 1984.

[Si85] G. J. Simmons, "The Subliminal Channel and Digital Signatures," InProceedings of Eurocrypt '84, T. Beth, N. Cot, I. Ingemarsson (Eds.),pages 364-378, Springer-Verlag, 1985.

[Si93] G. J. Simmons, "Subliminal Communication is Easy Using the DSA," Inproceedings of Eurocrypt '93, T. Helleseth (Ed.), pages 218-232,Springer-Verlag, 1993.

[YY96] A. Young, M. Yung, "The Dark Side of Black-Box Cryptography, or:Should we trust Capstone?" In proceedings of Crypto '96, Neal Koblitz(Ed.), Springer-Verlag, pages 89-103, 1996.