https://www.theregister.co.uk/2020/01/27/clipper_lessons_learned/

Enigma More than a quarter century after its introduction, the failed rollout of hardware deliberately backdoored by the NSA is still having an impact on the modern encryption debate.

Known as Clipper, the encryption chipset developed and championed by the US government only lasted a few years, from 1993 to 1996. However, the project remains a cautionary tale for security professionals and some policy-makers. In the latter case, however, the lessons appear to have been forgotten, Matt Blaze, McDevitt Professor of Computer Science and Law at Georgetown University in the US, told the USENIX Enigma security conference today in San Francisco.