KEY EXPIRY NUMBER (KEN)
The Key Expiry Number is an 8 bit binary number which is used to check whether the decoder key in a payment meter has expired. The Key expiry Number represents the last 8 bits of the TID field. If the most significant 8 bits of the TID value in the token are greater that the KEN stored in the payment meter, the token is rejected with a key expiry error.
The KEN bit positions in the token field are shown below in bold – all numbers in binary format unless otherwise stated:
| Class | Subclass | RND | TID | Amount | CRC |
| 00 | 0000 | 0101 | 110000000010101001010101 = 3148437 minutes (2016/12/11 15:49) |
0010011100010000 (1000 decimal as per amount formula in IEC62055-41) | 0001100101110000 (1970 Hex) |
Usage
|
Key Expiry Number (stored in the payment meter) |
KEN Value of token (most significant 8 bits of the 24 bit TID field) |
Token validity |
| 0xff (Hexadecimal) = 255 (decimal) = 11111111 (binary) | 0x00 – 0xff (01/01/1993 – 24/11/2024 20:15 for 1993 base date) 0x00 – 0xff (01/01/2014 – 24/11/2045 20:15 for 2014 base date) 0x00 – 0xff (01/01/2035 – 24/11/2066 20:15 for 2035 base date) |
token accepted since TID <= KEN (all tokens accepted. Effectively KEN is disabled if set to 0xff) |
|
0xaa (Hexadecimal) = 170 (decimal) = 10101010 (binary) |
0x00 – 0xaa (01/01/1993 – 08/03/2014 21:20 for 1993 base date) 0x00 – 0xaa (01/01/2014 – 08/03/2035 21:20 for 2014 base date) 0x00 – 0xaa (01/01/2035 – 08/03/2066 21:20 for 2035 base date) 0xab – 0xff (23/04/2014 21:36 – 24/11/2024 20:15 for 1993 base date) 0xab – 0xff (23/04/2035 21:36 – 24/11/2045 20:15 for 2014 base date) 0xab – 0xff (23/04/2066 21:36 – 24/11/2066 20:15 for 2035 base date) |
token accepted since TID <= KEN token accepted since TID <= KEN token accepted since TID <= KEN token rejected since TID > KEN token rejected since TID > KEN |
References: IEC62055-41