Understand Master&Session Keys

Master Key

• In a hierarchy of Key Encrypting Keys (KEKs) and Transaction Keys, the Master Key represents the highest level of KEK.

• Distribution Method: Master Keys are typically distributed using physical methods, such as key loading devices, PSAM card or smart card.

• Replacement: They are replaced using the same methods whenever compromise is suspected or confirmed.

Transaction Key (Session Key)

• A Transaction Key, often referred to as a Session Key, Data Key, communications key, or working key, is used to cryptographically process transactions.

• In scenarios where different cryptographic functions are used, each function might employ a variant of the Transaction Key.

Key Hierarchy

• Two-Layer Hierarchy:

  • There are two type of keys: Master Key and Session Key.

  • In the devices, the highest-level KEK is known as the Master Key.

  • The Master Key encrypts Transaction Keys (Session Keys) directly.

  • Session Keys: These include PIN keys (for encrypting PIN blocks), MAC keys (for MAC calculations), and data keys (for encrypting other data).

  • Each Master Key support three slots for Session Keys internally.

• Three-Layer Hierarchy:

  • There are three type of keys: Transport Key, Master Key and Session Key.

  • Highest Level: Referred to as a Transfer/Transport Key.

  • Middle Level: Known as a Master Key, which is encrypted and updated by Transport Key.

  • Lowest Level: Called a Session Key, which is encrypted and updated by the Master Key.

Groups of Keys

• The devices support 50 slots of Master/Session Keys.

Key Injection

• Master Key (Two-Layer) & Transfer/Transport Key (Three-Layer): For injecting these keys, refer to Use TMK KeyLoader POS or Understand Remote Key Injection.

• Session Key & Master Key (Three-Layer): These can be injected using our SDK. Refer to the PINPad section of our SDK for detailed instructions.

Usage

• For information on how to utilize these keys, please refer to the PINPad description in our SDK.