In the world of payment systems, keys and how they are used are important for transferring information from one place to another, storing information, and securing authorization and scripting steps.
Key types are divided into six categories based on their purpose:
Key Management Keys:
- LMK (Local Master Key)
- ZMK (Zone Master Key)
- TMK (Terminal Master Key)
Transaction Keys:
- Auth: Authentication Key
- SMI: Secure Message Integrity Key
- SMC: Secure Message Confidentiality Key
Symmetric Keys – Magstripe:
- CVV1/CVC1: Card Verification Value/Code 1 Key
- CVV2/CVC2: Card Verification Value/Code 2 Key
- iCVV: ICC Card Verification Value Key
- PVK: Pin Verification Key
Symmetric Keys – Authorization & Scripting:
- MDK-AC: Authentication Cryptogram Key
- MDK-MAC: Message Authentication Code Key
- MDK-ENC: Encipherment Key
- MDK-IDN: ICC Dynamic Number Key
- MDK-CVC3: Card Verification Code 3 Key
- MDK-dCVV: Dynamic Card Verification Value Key
Symmetric Keys – Personalization:
- KEK: Key Encryption Key
- PEK: Pin Encryption Key
Symmetric Keys – PIN Management:
- PEK: Pin Encryption Key
- TPK: Terminal Pin Key
- ZPK: Zone Pin Key
The logic of the key hierarchy
Higher-level keys (such as LMK) protect other keys. Lower-level keys, on the other hand, are used directly in transactions. This structure ensures that even if a lower-level key is compromised, the higher-level key remains secure.
Keys are changed at regular intervals, and old keys are securely destroyed. Each key must be used for a single purpose only; using the same key for both PIN and MAC violates security principles.
