Breaking and provably repairing the SSH authenticated encryption scheme: A case study of the Encode-then-Encrypt-and-MAC paradigm

  • Authors:
  • Mihir Bellare;Tadayoshi Kohno;Chanathip Namprempre

  • Affiliations:
  • University of California, San Diego, La Jolla, CA;University of California, San Diego, La Jolla, CA;Thammasat University, Patumtani, Thailand

  • Venue:
  • ACM Transactions on Information and System Security (TISSEC)
  • Year:
  • 2004

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Abstract

The secure shell (SSH) protocol is one of the most popular cryptographic protocols on the Internet. Unfortunately, the current SSH authenticated encryption mechanism is insecure. In this paper, we propose several fixes to the SSH protocol and, using techniques from modern cryptography, we prove that our modified versions of SSH meet strong new chosen-ciphertext privacy and integrity requirements. Furthermore, our proposed fixes will require relatively little modification to the SSH protocol and to SSH implementations. We believe that our new notions of privacy and integrity for encryption schemes with stateful decryption algorithms will be of independent interest.