ProblemsCBCModeForPANs

1. Abstract

    * Permanant Account Number (PAN) encryption in an ecommerce merchant
      databases presents unique application issues.

    * Block encryption primitives using Cipher Block Chaining (CBC) mode
      preclude the possibility of supporting an efficient lookup
      functionality.

    * Since CBC encryption mode is not idempotent [8][1] one way hashes for
      PANs are needed in order to support lookup.

    * The payment community does not view a one way hash of a PAN as a
      security violation. Ironicaly, its use is recommended by PCI DSS best
      practices.

    * On the other hand, security experts categorically proscribe the use of
      an idempotent block cipher implementation such as Electronic Code Book
      (ECB).

    * Storage of SHA1 hashes for payment information follows best practise,
      PCI guidelines and buzzword compliance.

    * This paper presents a minority opinion and argues that security is
      weakened dramatically by employing one way cryptographic primitives
      for PANs in order to support lookup.