Cryptology ePrint Archive: Report 2013/269

Chosen Ciphertext Secure (CCS): Stateful Symmetric Key CCA Encryption with Minimal Ciphertext Expansion

Jonathan Trostle

Abstract: In some wireless environments, minimizing the size of messages is paramount due to the resulting significant energy savings. We present a new stateful symmetric encryption scheme: CCS or Chosen Ciphertext Secure scheme. CCS has the property that modifications to the ciphertext randomizes the resulting plaintext. Using this property, we prove the scheme is CCA2 secure. Thus we obtain CCA2 encryption schemes with minimal ciphertext expansion which are applicable to resource constrained wireless environments. For protocols that send short messages, our scheme is similar to Counter with CBC-MAC (CCM) for computation but has much shorter messages (since we can use much smaller or no MAC tags) for a similar level of security. A key idea is that various protocol fields in the underlying plaintext act as an authentication tag given changes to the message ciphertext. To the best of our knowledge, CCS is the first scheme that achieves CCA2 security with only 2-3 bytes of ciphertext expansion.

Category / Keywords: secret-key cryptography / Private key CCA2 encryption, energy constrained cryptography, authenticated encryption

Publication Info: Has not been published elsewhere

Date: received 11 May 2013, last revised 3 Oct 2013

Contact author: jon49175 at yahoo com

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Version: 20131003:165740 (All versions of this report)

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