The source code to the cryptotrojan is still live on the Internet and is associated with a draft of Chapter 2.
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Covert information leakage attacks carried out by cryptoviruses, cryptotrojans, and cryptoworms that, by definition, contain and use the public key of the attacker is a major theme in cryptovirology. In "deniable password snatching", a cryptovirus installs a cryptotrojan that asymmetrically encrypts host data and covertly broadcasts it. This makes it available to everyone, noticeable by no one (except the attacker), and only decipherable by the attacker. An attacker caught installing the cryptotrojan claims to be a virus victim.
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The EC-DRBG algorithm utilizes the discrete-log kleptogram from Kleptography which by definition makes the EC-DRBG a cryptotrojan. Like ransomware, the EC-DRBG cryptotrojan contains and uses the attacker's public key to attack the host system. The cryptographer Ari Juels indicated that NSA effectively orchestrated a kleptographic attack on users of the Dual EC DRBG pseudorandom number generation algorithm and that, although security professionals and developers have been testing and implementing kleptographic attacks since 1996, "you would be hard-pressed to find one in actual use until now". Due to public outcry about this cryptovirology attack, NIST rescinded the EC-DRBG algorithm from the NIST SP 800-90 standard.
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However, this provision was removed from the final version of the bill. A minor in Japan was arrested for creating and distributing ransomware code. Young and Yung have had the ANSI C source code to a ransomware cryptotrojan on-line, at cryptovirology.com, since 2005 as part of a cryptovirology book being written.
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Researchers devised several methods for solving this problem. They presented a deniable password snatching attack in which the keystroke logging trojan is installed using a virus or worm. An attacker who is caught with the virus or worm can claim to be a victim. The cryptotrojan asymmetrically encrypts the pilfered login/password pairs using the public key of the trojan author and covertly broadcasts the resulting ciphertext.
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An attacker observed receiving the covert asymmetric broadcast is one of thousands, if not millions of receivers, and exhibits no identifying information whatsoever. The cryptovirology attack achieves "end-to-end deniability". It is a covert asymmetric broadcast of the victim's data. Cryptovirology also encompasses the use of private information retrieval (PIR) to allow cryptoviruses to search for and steal host data without revealing the data searched for even when the cryptotrojan is under constant surveillance.
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Kleptographic attacks can be constructed as a cryptotrojan that infects a cryptosystem and opens a backdoor for the attacker, or can be implemented by the manufacturer of a cryptosystem. The attack does not necessarily have to reveal the entirety of the cryptosystem's output; a more complicated attack technique may alternate between producing uninfected output and insecure data with the backdoor present.A. Young, M. Yung, Malicious Cryptography: Exposing Cryptovirology, John Wiley & Sons, 2004.
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A. Young, M. Yung, "Cryptovirology: Extortion-Based Security Threats and Countermeasures," In: McHugh J, Dinolt G (eds) Symposium on Security & Privacy. IEEE Computer Society Press, Washington DC, pages 129-141, 1996. A cryptovirus, cryptotrojan, or cryptoworm hybrid encrypts the victim's files using the public key of the author and the victim must pay (with money, information, etc.) to obtain the needed session key. This is one of many attacks, both overt and covert, in the field known as Cryptovirology.
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