If you are being prompted to enter the 32 hex digits for a CVV encryption key (MDK), you are likely working within a Hardware Security Module (HSM) environment or configuring a payment gateway. Here is everything you need to know about what this key is, why it is 32 characters long, and how it protects financial transactions. What is the CVV Encryption Key (MDK)?
Restricts input strictly to 0-9 and A-F (ignores all other keystrokes).