I Entered a Fake CVV — Here’s Why the Bank Immediately Rejected It

**Recently, I ran into something interesting while adding a credit card to an online payment system. I wasn’t making a purchase — just saving the card. Out of curiosity, I entered a fake CVV. The card was immediately declined.** That raised an important technical question: - Is CVV really verified even when no payment is made? - How is CVV generated by banks? - How does CVV verification actually work? This article breaks down the technical process of CVV generation and validation, including the cryptographic mechanisms used by banks and card networks like Visa and Mastercard. What Is CVV in Payment Systems? As Undergraduate I thought CVV as: “Just a 3-digit security number on the back of the card.” Technically, that’s not accurate. CVV (Card Verification Value) is a cryptographic value generated by the issuing bank using: PAN (Primary Account Number – card number) Expiry date Service code A secret cryptographic key (known only to the bank) DES or 3DES encryption A Hardware Security Mod