Format Preserving Encryption

Encrypting Personally Identifiable Information (PII) in large databases has historically been difficult, because encrypting information typically implies expanding data and changing its format. Previous attempts to encrypt PII data like credit card numbers and Social Security Numbers without changing their format have used questionable cryptographic constructions. We examine the security model for this problem, extend a construction by Black and Rogaway, and propose practical constructions for encrypting credit card numbers and Social Security Numbers.