NIST Special Publication 800-38A
R
ecommendation for Block
2001 Edition
C
ipher Modes of Operation
M
ethods and Techniques
M
orris Dworkin
C O M P U T E R S E C U R I T Y
C O M P U T E R S E C U R I T Y
Computer Security Division
Information Technology Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899-8930
December 2001
U.S. Department of Commerce
Donald L. Evans, Secretary
Technology Administration
Phillip J. Bond, Under Secretary of Commerce for Technology
National Institute of Standards and Technology
Arden L. Bement, Jr., Director
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Reports on Information Security Technology
The Information Technology Laboratory (ITL) at the National Institute of Standards and Technology
(NIST) promotes the U.S. economy and public welfare by providing technical leadership for the Nation’s
measurement and standards infrastructure. ITL develops tests, test methods, reference data, proof of
concept implementations, and technical analyses to advance the development and productive use of
information technology. ITL’s responsibilities include the development of technical, physical,
administrative, and management standards and guidelines for the cost-effective security and privacy of
sensitive unclassified information in Federal computer systems. This Special Publication 800-series
reports on ITL’s research, guidance, and outreach efforts in computer security, and its collaborative
activities with industry, government, and academic organizations.
Certain commercial entities, equipment, or materials may be identified in this document in order to describe an
experimental procedure or concept adequately. Such identification is not intended to imply recommendation or
endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities,
materials, or equipment are necessarily the best available for the purpose.
National Institute of Standards and Technology Special Publication 800-38A 2001 ED
Natl. Inst. Stand. Technol. Spec. Publ. 800-38A 2001 ED, 66 pages (December 2001)
CODEN: NSPUE2
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WASHINGTON: 2001
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Abstract
This recommendation defines five confidentiality modes of operation for use with an underlying
symmetric key block cipher algorithm: Electronic Codebook (ECB), Cipher Block Chaining
(CBC), Cipher Feedback (CFB), Output Feedback (OFB), and Counter (CTR). Used with an
underlying block cipher algorithm that is approved in a Federal Information Processing Standard
(FIPS), these modes can provide cryptographic protection for sensitive, but unclassified,
computer data.
KEY WORDS: Computer security; cryptography; data security; block cipher; encryption;
Federal Information Processing Standard; mode of operation.
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