A decoder Key (DK) is a 64 or 128 bit key used in the encryption or decryption of tokens. It is generated using one of several Decoder Key Generation Algorithms as specified in IEC62055-41. The DK may have several types: see Key Type.
The meter key is generated by the security module and must never be visible to the manufacturer or the user. It is created using the meter number and the Supply Group Code, and other key parameters of the vending key.