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Encyclopedia > OCB mode

OCB mode (Offset Codebook Mode) is a mode of operation for cryptographic block ciphers. In cryptography, a block cipher operates on blocks of fixed length, often 64 or 128 bits. ... In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ...

Contents


Encryption and authentication

It was designed to provide both authentication and privacy. In simplified and basic terms, it is a scheme for integrating a Message Authentication Code (MAC) into the operation of a block cipher. In this way, OCB mode alleviates the need to use the two traditionally separate systems of a MAC's for authentication and block cipher encryption for privacy. This simplifies the secure communication process for end users. Authentication is the act of establishing or confirming something or someone as authentic. ... Privacy is the ability of an individual or group to stop information about themselves from becoming known to people other than those they choose to give the information to. ... A cryptographic message authentication code (MAC) is a short piece of information used to authenticate a message. ... In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ... In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ... In cryptography, encryption is the process of obscuring information to make it unreadable without special knowledge. ...


OCB mode was designed by Phillip Rogaway, who credits Mihir Bellare, John Black, and Ted Krovetz with assistance and feedback on designs.


There are two versions of OCB: 1.0 and 2.0. OCB 2.0 improves on 1.0 by allowing associated data along with the message — that is, data that are authenticated but not encrypted — and a new method for generating a sequence of offsets. OCB 2.0 was first published in 2003, originally named AEM (Authenticated-Encryption Mode, or Advanced Encryption Mode). 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ...


OCB mode is listed as an optional method in the IEEE 802.11 wireless security standard. The Institute of Electrical and Electronics Engineers or IEEE (pronounced as eye-triple-ee) is an international non-profit, professional organization incorporated in the State of New York, United States. ... IEEE 802. ...


Patents

A patent application is in place for OCB mode. However, a special exemption has been granted so that OCB mode can be used in software licensed under the GNU General Public License without cost, as well as in software not developed and not sold inside the United States [1]. The GNU logo The GNU General Public License (GNU GPL or simply GPL) is probably the most popular free software license, originally written by Richard Stallman for the GNU project. ...


Performance

OCB performance overhead is minimal comparing to classical, non-authenticating modes like CBC. OCB requires one block cipher encryption per each block of encrypted and authenticated message and one encryption per each block of additional associated data. There are two also extra encryptions added once at the end of process. In cryptography, a block cipher operates on blocks of fixed length, often 64 or 128 bits. ...


For comparison, CCM mode offering similiar functionality requires twice as more encryptions per each message block (associated data requires one as in OCB). CCM mode (Counter with CBC-MAC) is a mode of operation for cryptographic block ciphers. ...


See also

CCM mode (Counter with CBC-MAC) is a mode of operation for cryptographic block ciphers. ...

External links

  • OCB homepage
  • OCB FAQ

References

  • Phillip Rogaway, Mihir Bellare, John Black. OCB: A block-cipher mode of operation for efficient authenticated encryption, ACM Transactions on Information and System Security (TISSEC), Volume 6, Issue 3, pp.365-403. August 2003.


Block ciphers edit
Algorithms: 3-Way | AES | Akelarre | Anubis | Blowfish | Camellia | CAST-128 | CAST-256 | CMEA | CS-Cipher | DEAL | DES | DES-X | FEAL | FOX | FROG | G-DES | GOST | ICE | IDEA | Iraqi | KASUMI | KHAZAD | Khufu and Khafre | LOKI89/91 | LOKI97 | Lucifer | MacGuffin | Madryga | MAGENTA | MARS | MISTY1 | MMB | NewDES | Noekeon | RC2 | RC5 | RC6 | REDOC | Red Pike | S-1 | SAFER | SEED | Serpent | SHACAL | SHARK | Skipjack | Square | TEA | Triple DES | Twofish | XTEA
Design: Feistel network | Key schedule | Product cipher | S-box | SPN   Attacks: Brute force | Linear / Differential cryptanalysis | Mod n | Related key | XSL   Standardization: AES process | CRYPTREC | NESSIE   Misc: Avalanche effect | Block size | IV | Key size | Modes of operation | Piling-up lemma | Weak key

  Results from FactBites:
 
Block cipher modes of operation - Wikipedia, the free encyclopedia (1970 words)
In CBC mode, the IV must, in addition, be randomly generated at encryption time.
Because each stage of the CFB mode depends on the encrypted value of the previous ciphertext XORed with the current plaintext value, a form of pipelining is possible, since the only encryption step which requires the plaintext is the final XOR.
These authenticated encryption modes are classified as single pass modes or double pass modes.
  More results at FactBites »

 
 

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