A FULLY FUNCTIONAL HAGELIN CD-57 POCKET CIPHER DEVICE. Developed by Boris Hagelin in 1957, the eponymous Hagelin CD-57 was a mechanically operated, pin-and-lug pocket cipher machine that remained in service until the mid 1970s. By secret arrangement with the United States National Security Agency, two primary versions of this device were made; the CD-57, made for use by NATO and NATO-friendly countries, and the CD-55, made for use by non-NATO countries. The two appeared identical, however the CD-55 was much easier to break; the CD-57, basically a pocket-version of Hagelin's unbreakable CX-52 desktop cipher machine, featured a highly improved stepping mechanism and could quickly be converted to an unbreakable one-time tape (OTT) cipher machine by replacing the 6-wheel stack with the so-called RT/CD (Random Tape) option and fitting the bottom of the case with a key tape cassette.
Because of its easily concealable size, the CD-57 was popular with a number of intelligence agencies during the cold War, as well as with many European and other armies.