ProblemsCBCModeForPANs

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Author Ashok Misra

 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, 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.