Each payment meter contains a decoder key that is used to decrypt tokens input via the keypad or other token input methods.
The decoder key for a payment meter is initially installed into payment meter by means of keychange tokens. The decoder key is created using a DecoderKeyGenerationAlgorithm (DKGA). There are several decoder key types and are generated using the DKGA.
The meter key may either be 64 bits in length (for EA07), or 128 bits in length (for EA11), and uses the following parameters to create it:
1. Supply Group Code (SGC)
2. Tariff Index (TI)
3. Key Type (KT)
4. Key Revision Number (KRN)
5. Decoder reference number (DRN)
6. Vending key (VK)
See IEC62055-41 for the DKGA algorithms used.