scope:

The ANS X9.124 standard defines a collection of methods for encrypting data strings so that the length and the character set for the ciphertext is the same as those of the plaintext. This is called format-preserving encryption (FPE). These methods are useful in situations where fixed-format data, such as Primary Account Numbers (PANs) or Social Security Numbers (SSNs), must be encrypted, but there is a requirement to limit changes to existing communication protocols, database schemata or application code.

Part 1 of this standard includes a set of definitions common to all FPE techniques, a security model for FPE block cipher techniques, and a description of the pseudocode language used in defining the mode specified in this document.

Part 2 of this standard defines Format-Preserving Encryption - Counter Mode (FPCM) which is a key stream with counter mode method for format-preserving encryption.

Part 3 of this standard defines FF1 mode, which is a block cipher-based format-preserving Feistel-based mode.

Part 4 of this standard defines FF2.1 mode, which is a block cipher-based format-preserving Feistel-based mode.

Part 5 of this standard defines FF3.1 mode, which is a block cipher-based format-preserving Feistel-based mode.

Purpose

The purpose of this standard is to provide approved methods for format-preserving encryption (FPE).