Cryptology ePrint Archive: Report 2000/039

Encryption Modes with Almost Free Message Integrity

Charanjit S. Jutla

Abstract: We define a new mode of operation for block encryption which in addition to assuring confidentiality also assures message integrity. In contrast, previously for message integrity a separate pass was required to compute a cryptographic message authentication code (MAC). The new mode of operation, called Integrity Aware CBC (IACBC), requires a total of m + log m block encryptions on a plaintext of length m blocks. The well known CBC (cipher block chaining) mode requires m block encryptions. The second pass of computing the MAC essentially requires additional m block encryptions. We also show a lower bound of \Omega(log m) additional block encryptions for any reasonably modeled (linear) scheme which assures message integrity along with confidentiality.

Category / Keywords: secret-key cryptography / Block cipher, CBC, authentication, MAC, modes of operation

Date: received 1 Aug 2000

Contact author: csjutla at watson ibm com

Available format(s): Postscript (PS) | Compressed Postscript (PS.GZ) | BibTeX Citation

Version: 20000801:174658 (All versions of this report)

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