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Announcing a Workshop on Modes of Operation for Symmetric Key Block Cipher Algorithms

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National Institute of Standards and Technology, Doc.


Notice of public workshop; request for comments.


The National Institute of Standards and Technology (NIST) announces a workshop to discuss modes of operation for the protection of data using a symmetric key block cipher algorithm. The results of this workshop will be used by NIST in development a draft modes of operation standard for symmetric key block cipher algorithms. Comments and papers are encouraged prior to the workshop to propose, define, and justify any modes that are appropriate for NIST to include in such a standard. These comments and papers should be addressed to

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The Modes of Operation workshop will be held on Friday, October 20, 2000, from 9 a.m. to 5 p.m.

To provide for sufficient time to prepare the agenda for the modes to be discussed at the workshop, comments are due by October 1, 2000.


The workshop will be held at the Baltimore Convention Center in Baltimore, Maryland. Details regarding workshop registration can be found at:​modes.

Comments regarding proposed modes of operation may be sent to: or to Elaine Barker, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8930, Gaithersburg, MD 20899-8930, USA.

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The Symmetric Key Block Cipher Modes of Operation home page (​modes) may be used to access information regarding the modes of operation workshop, registration and lodging information.

Questions may also be addressed to: 1) Elaine Barker at (301) 975-2911 (Email: or Bill Burr at (301) 975-2914 (Email:

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In 1997, NIST began the development of the Advanced Encryption Standard (AES) to specify a symmetric key block cipher algorithm that would provide confidentiality for sensitive (unclassified) data. As the AES development process nears its conclusion, the specific modes of operation for its use need to be addressed. In 1980, Federal Information Processing Standard (FIPS) 81, DES Modes of Operation, defined four encryption modes for the Data Encryption Standard (DES). The four modes are the Electronic Codebook (ECB) mode, the Cipher Block Chaining (CBC) mode, the Cipher Feedback (CFB) mode, and the Output Feedback (OFB) mode. Each mode of FIPS 81 specifies a different way to use the DES block encryption algorithm to encrypt and decrypt data, with somewhat different security and operational characteristics, and each is best suited to different applications. Cryptographic system designers or security application designers need to select one or more of the modes when using the DES symmetric key block cipher algorithm in a cryptographic system or security application. However, FIPS 81 was written to be specific to DES and its key and block size. A new standard is needed that will address other symmetric key block cipher algorithms (e.g., AES). The workshop will provide NIST with useful input as the standard is drafted.

It is NIST's intention that the planned standard be independent of specific key or block sizes of particular encryption algorithms and that the standard include the four modes specified in FIPS 81, plus other modes needed for current applications and technology. During the development of the AES, NIST received comments suggesting that additional modes should be included in a Modes of Operation standard, and that the development of a new modes standard should be carefully considered by the cryptographic community. To this end, the workshop will discuss appropriate secure modes that participants believe NIST should consider for the standard. Comments are requested prior to the workshop on any recommended modes so as to facilitate discussion of specific proposals at the workshop. Following the workshop, NIST intends to prepare a draft standard that will be made available for public review and comment.

Advance registration and a workshop fee is required for workshop attendance. Details of the workshop may be obtained at​modes. Note that this workshop follows the National Information Systems Security Conference (NISSC) held in Baltimore, Maryland from October 16-19, 2000.

NIST solicits comments from interested parties, including industry, academia, voluntary standards organizations, the public, Federal agencies, and State and local governments concerning the Modes of Operation Standard issues and techniques for discussion at the workshop.

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Authority: NIST's activities to develop computer security standards to protect Federal sensitive (unclassified) systems are undertaken pursuant to specific responsibilities assigned to NIST in Section 5131 of the Information Technology Management Reform Act of 1996 (Pub. L. 104-106), the Computer Security of 1987 (Pub. L. 100-235), and Appendix III to Office of Management and Budget Circular A-130.

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Dated: July 18, 2000.

Karen H. Brown,

Deputy Director, NIST.

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[FR Doc. 00-18811 Filed 7-24-00; 8:45 am]