What is a Clipper Chip?

The Clipper Chip was a controversial encryption device promoted by the U.S. Government for use in the telecommunications industry. It used small pieces of information known as keys to encrypt calls, shielding them from interception and eavesdropping. The technology was designed with a special “backdoor” that would allow law enforcement to break the encryption with a warrant or other legal authorization. A diverse group of opponents criticized the proposal on privacy and security grounds, and the system was abandoned within just a few years of its announcement.

Approved by the Clinton administration in 1993, the Clipper Chip was touted as a way for individuals, businesses, and government entities to protect phone calls from eavesdropping. It consisted of a small microchip called a cryptoprocessor that could be embedded into phones and encrypt voice communications using “keys,” pieces of information that control the output of mathematical encryption algorithms. Without the correct key, other devices or someone eavesdropping on the call would hear only a scrambled signal.

The encryption algorithm used in the Clipper Chip was designed by the National Security Agency (NSA), a highly secretive arm of the US government that deals with electronic espionage and surveillance. The NSA’s algorithm, known as “Skipjack,” was similar to technologies developed in the private sector with one notable exception: Skipjack was designed to give federal law enforcement and antiterrorism agents a “backdoor” that could be used to access calls encrypted with the Clipper Chip. For each Clipper-compatible device sold, a key capable of breaking that device’s encryption would be split in half and kept “in escrow” by the government, with one portion held by the Treasury Department’s Automated Systems Division and the other in the hands of the National Institute of Standards and Technology. With a warrant or other legal authorization, agencies like the Federal Bureau of Investigation (FBI) could retrieve the keys and monitor encrypted calls of suspects.

This key escrow concept generated opposition from right-wing talk show hosts, civil liberties groups, business leaders, and electronic privacy advocates. Many critics argued that the inclusion of a backdoor was a threat to both privacy and security, while others accused the government of trying to stifle private encryption technologies by purchasing tens of thousands of Clipper-enabled devices while maintaining a ban on exports of advanced encryption software. Government officials countered that, without such a program, terrorists and organized crime rings would thwart legal wiretapping efforts with impenetrable encryption.

By 1996, the US government had abandoned the Clipper Chip proposal. During the three-year period of debate and controversy over the program, the chip had only been included in a single model of phones produced by AT&T. The effectiveness and security of the proposed encryption device was called into question when an AT&T researcher demonstrated that a sophisticated criminal could exploit vulnerabilities in the system and make it impossible for law enforcement to intercept communications. Though the Clipper Chip itself was abandoned, debate over the relationship between encryption and law enforcement has continued.