A software protection dongle (commonly known as a dongle or key) is an electronic copy protection and content protection device. When connected to a computer or other electronics, they unlock software functionality or decode content. The hardware key is programmed with a product key or other cryptographic protection mechanism and functions via an electrical connector to an external bus of the computer or appliance.

In software protection, dongles are two-interface security tokens with transient data flow with a pull communication that reads security data from the dongle. In the absence of these dongles, certain software may run only in a restricted mode, or not at all. In addition to software protection, dongles can enable functions in electronic devices, such as receiving and processing encoded video streams on television sets.