User's Manual

Chips and readers- USER’S GUIDE
UG 21
Version 1.0
APPENDIX A
HOW TO LOAD A KEY IN A
COUPLER
This procedure consists in several operations on the key. The final result will be sent to
the coupler using the Loag_Key_File function.
EXCHANGE KEY
To ensure the security, an exchange key will protect all key loading operations.
This key is in the coupler memory and has 2 functions :
- only host knowing this key will be able to modify the Debit and Credit keys.
- New key value are encrypted with this exchange key so it is not possible to
read the new value on the serial line.
You have to know this exchange key to modify the value of any other key. For any
modification, the Exchange key is managed exactly as the Debit key and the Credit key
: you have to use the Key Loading Procedure described in the next paragraphs.
GENERAL KEY LOADING PROCEDURE
Before the key loading starts with the LOAD_KEY_FILE command, the host must
generate a session key. This key is generated by the encryption of the current Exchange
Key (Ke) with an 8-byte random number.
Reader
New key
value (Kx)
Exchange
key (Ke)
Exchange
key (Ke)
Ask random
Calculate the
session key
Encrypt the new
key value
Calculate
encrypted key
checksum
Load encrypted
key and
checksum
Decrypt new key
value
Calculate
checksum
Compare
checksum
Calculate the
session ley
Host
Random
(Rnd)