Black Hat Briefings, Las Vegas 2005 [audio] Presentations From The Security Conference

This talk will present recent advances in the design of robust cryptographic backdoors in secret symmetric ciphers (i.e., classified or proprietary ciphers). The problem directly affects end-users since corporations and governments have in the past produced secret symmetric ciphers for general use (e.g., RC4 and Skipjack, respectively). The problem itself is challenging since it involves leaking secret key material in the ciphertexts that are produced by a deterministic function, whereas traditional subliminal channels have relied on the use of randomized cryptographic algorithms. Such attacks can be regarded as advanced Trojan horse attacks since the secret block cipher securely and subliminally transmits the symmetric key of the sender and receiver to the malicious designer and confidentiality holds even when the cipher is made public. The material that will be surveyed was published in Fast Software Encryption (FSE '98), the Australasian Conference on Information Security and Privacy (ACISP '03), and Se