The TSEC/KY-68, also known as Digital Subscriber Voice Terminal is a rugged semi-and full-duplex telephone system of the U.S. armed forces. In the device a Ver-/Entschlüsselungs-Modul for safe connection is installed.

It transmits voice or data at a rate of 16 or 32 kbit / s, speech is converted into a digital signal. The KY -68 can be operated in civilian or military exchanges in encrypted or unencrypted mode. Alternatively, there is the possibility of direct connection, this is only possible in encrypted mode.

Although it is used primarily for encrypted connections, the KY -68 can also connect to an unsecured, digital telephone (Digital Non -secure Voice Terminal, DNVT ). A local exchange alerts the user of a KY -68 with a sound signal when a connection with a non- secure telephone is established.

The KY- 68 is at a communication interface, typically a KYK -13 or AN/CYZ-10 used.

An almost identical version of a lighter material exists as an office version under the name KY -78.

The phones KY -68 and KY -78 are both approved for the exchange of information up to the SECRET classification, and despite the compromise in the early 1990s, both versions still seem to be in use.