Block Cipher Modes

A block cipher mode, or mode, for short, is an algorithm that features the use of a symmetric key block cipher algorithm to provide an information service, such as confidentiality or authentication.

With the advent of new block ciphers, such as the Advanced Encryption Standard (AES), there is a need to update long-standing modes of operation and an opportunity to consider the development of new modes.

NIST is in the process of recommending modes in a series of special publications. The documents in this series, and other information that relevant to the modes development process, are summarized below.

Currently, there are eight approved block cipher modes that may be used with NIST's approved encryption algorithms: five modes for confidentiality, one for authentication, and two combined modes for confidentiality and authentication.

Current Modes

• FIPS 81, December 1980.
  
  

  FIPS 81 specifies four confidentiality modes of operation for the DES cipher, which has subsequently been withdrawn. The modes are ECB, CBC, CFB, and OFB.

• SP 800-38A 2001 ED, December 2001.

  In SP 800-38A, five confidentiality modes are specified for use with any approved block cipher: the CTR mode and updated versions of the four modes in FIPS 81.

• SP 800-38B, May 2005.

  In SP 800-38B, the CMAC authentication mode is specified for use with any approved block cipher.

• SP 800-38C, May 2004

  SP 800-38C specifies the CCM mode, an authenticated encryption mode of the AES algorithm.

• SP 800-38D, November 2007

  SP 800-38D specifies GCM, an authenticated encryption mode of the AES algorithm.