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Denning privately reviewed, at federal request, the Skipjack block cipher, as part of the controversial Clipper chip initiative, put forth by the NSA for encryption of private communications. In Congressional testimony, she stated that general publication of the algorithm would enable someone to build a hardware or software product that used SKIPJACK without escrowing keys. In public forums, such as the Usenet forum comp.risks, she defended this program. Denning also served as a witness in the 1990 trial of United States v. Riggs. Her testimony was instrumental in leading the government to drop charges against defendant Craig Neidorf.
Denning, Dorothy Elizabeth Robling (1982). Cryptography and Data Security. Addison-Wesley. ISBN0-201-10150-5.
Denning, Dorothy Elizabeth Robling (1990). Concerning Hackers Who Break into Computer Systems. presented at the 13th National Computer Security Conference, Washington, D.C. Digital Equipment Systems Research Center.
Ruritania, a classic Internet satire of Denning's opposition to citizen cryptography
Declaration on Encryption Policy, a 1997 declaration in which Denning said that she did not recommend domestic restrictions on the use encryption within the United States, so long as all crypto keys are legally required to be accessible to the government by court order.