I am currently researching my studentcard. Money is stored on this card.
But the vending machine also checks a checksum on the card. I already did a lot of effort to find it but didn't succeed.
I did some testing with changing the values and this what I concluded from it:
- Transaction byte is used in the checksum
- Money is also used in the checksum
- Some unique value from the card is also used.
Thanks for any help! Meanwhile I will keep breaking my head :)