Dog race tracks often employ Automatic Betting Machines (ABMs),18 which are somewhat analogous to ATM machines. An ABM is a terminal where Alice can place her own bets and scan her winning tickets. An...

Dog race tracks often employ Automatic Betting Machines (ABMs),18 which are somewhat analogous to ATM machines. An ABM is a terminal where Alice can place her own bets and scan her winning tickets. An ABM does not accept or dispense cash. Instead, an ABM only accepts and dispenses vouchers. A voucher can also be purchased from a special voucher machine for cash, but a voucher can only be redeemed for cash by a human teller. A voucher includes 15 hexadecimal digits, which can be read by a human or scanned by a machine—the machine reads a bar code on the voucher. When a voucher is redeemed, the information is recorded in a voucher database and a paper receipt is printed. For security reasons, the (human) teller must submit the paper receipt which serves as the physical record that the voucher was cashed. A voucher is valid for one year from its date of issue. However, the older that a voucher is, the more likely that it has been lost and will never be redeemed. Since vouchers are printed on cheap paper, they are often damaged to the point where they fail to scan, and they can even be difficult for human tellers to process manually. A list of all outstanding vouchers is kept in a database. Any human teller can read the first 10 hex digits from this database for any outstanding voucher. But, for security reasons, the last five hex digits are not available to tellers.