Key defines encryption key information in KeyIndicator, KeyValue format where KeyIndicator is a number from 0 to 15 and KeyValue is a string used to derive the encryption key, called Kpseu in 3GPP TS 33.402. When KeyValue is exactly 32 hexadecimal characters, it is used directly as the key. Otherwise it is made 16 octets long.

KeyValue supports special % formatting characters. This is typically used to include the key as a variable so that it's not directly visible in the configuration file. See the configuration example for more information.