Announcement of NIST Modes Recommendation

Morris Dworkin dworkin at
Thu Dec 13 10:19:03 EST 2001

Now that the AES FIPS has been approved, here is an update from NIST on 
modes of operation.

The NIST special publication SP 800-38A, "Recommendation for Block Cipher 
Modes of Operation," is available online, at   Five 
confidentiality modes are specified for use with any FIPS-approved block 
cipher, such as the AES. The modes in SP 800-38A are updated versions of 
the ECB, CBC, CFB, and OFB modes that are specified in FIPS Pub. 81; in 
addition, SP 800-38A specifies the CTR mode.

NIST also expects to publish a 2002 edition of SP 800-38A in which the 
domain of the CBC mode is extended (to include plaintexts whose bit lengths 
are not a multiple of the block size); all of the technical material that 
is specified in the 2001 edition is expected to remain valid.

The next document in the series, SP 800-38B, will specify a variant of the 
CBC-MAC authentication mode.

Modes development is expected be an ongoing effort; later parts of the 
series may be devoted to the specification of new modes.


Morris Dworkin

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