This document describes a method consistent with the requirements of ANS X9.24 Retail Financial Services Symmetric Key Management Part 1 for the secure exchange of keys and other sensitive data between two devices that share a symmetric key exchange key. This method may also be used for the storage of keys under a symmetric key. This method is designed to operate within the existing capabilities of devices used in the retail financial services industry. This document is not a security standard and is not intended to establish security requirements. It is intended instead to provide an interoperable method of implementing security requirements and policies.

About the 2009 supplement:
This supplement contains clarifications to the proper usage of keys utilized to protect the key block defined in TR-31. TR-31 should be read with these clarifications taken into account.