ANSI X9。124标准定义了一组加密数据字符串的方法，以便密文的长度和字符集与明文相同。这被称为格式保留加密（FPE）。在必须加密固定格式数据（如主帐号（PAN）或社会安全号码（SSN））的情况下，这些方法非常有用，但需要限制对现有通信协议、数据库模式或应用程序代码的更改。本标准第1部分包括所有FPE技术通用的一组定义、FPE分组密码技术的安全模型，以及定义本文件中指定模式时使用的伪码语言的描述。

The ANSI 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.