SKIPJACK is the encryption algorithm in the Clipper Chip (MYK-78), a backdoor device that was supposed to be installed in all US manufactured cellphones but failed amid public scrutiny.
Since SKIPJACK was classified SECRET at the time, it did not undergo peer review. At the time, the government did reveal that it was a symmetric, 80-bit block cipher similar to DES that used public-key cryptography (PKC) for the key exchange.
The Clipper chip was developed by the NSA and proposed by the Clinton administration. The proposed scenario called for the device’s installation in all US-manufactured cell phones so that, upon the authorities’ securing of a warrant, law enforcement would simply activate its backdoor to facilitate eavesdropping on terrorism suspects’ conversations. The failure of SKIPJACK, a NSA-developed block cipher, to undergo peer review by the encryption community was one of the reasons the Clipper chip was rejected.
“The Clipper Chip failed in part due to reservations about SKIPJACK, its NSA-developed encryption algorithm. For a time SKIPJACK was unavailable for public scrutiny. The recommended key-sharing was also flawed, as reports alleged the device could be used by suspects to encrypt chatter so that the authorities were locked out.”