International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Encryption Modes with Almost Free Message Integrity

Charanjit S. Jutla
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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.
  title={Encryption Modes with Almost Free Message Integrity},
  booktitle={IACR Eprint archive},
  keywords={secret-key cryptography / Block cipher, CBC, authentication, MAC, modes of operation},
  note={ 11170 received 1 Aug 2000},
  author={Charanjit S. Jutla},