Cryptologic History Calendar
1993: Clinton administration proposed "Clipper Chip" method
From Wikipedia: The Clipper Chip was a chipset that was developed as an encryption device that secured “voice and data messages," with a built-in backdoor. It was intended to be adopted by telecommunications companies for voice transmission. It could not only encode messages but decode them as well. It was part of a Clinton Administration program to “allow Federal, State, and local law enforcement officials the ability to decode intercepted voice and data transmissions." Each clipper chip had] a unique serial number and a secret ‘unit key,’ programmed into the chip when manufactured." This way, each device was meant to be different from the next. It was announced in 1993 and by 1996 was entirely defunct.
Learn more via the links below.