A Practical Forward-Secure Public-Key Encryption Scheme with Untrusted Update

In open network, cryptographic operations are often performed on insecure, unprotected, and easily-stolen devices, therefore the threat of secret key exposure becomes more and more acute. The paradigm of forward security provides a promising approach to deal with the secret key exposure. This new paradigm guarantees that the compromise of current secret keys does not compromise past secret keys and past communications. Therefore, forward-security can minimize the resulting damage caused by the secret key exposure. In this paper, we present a practical forward-secure public-key encryption (FS-PKE) scheme and prove it to be forward-secure against selectivetime period and adaptive chosen plaintext attacks in the standard model. The main performance parameters of our proposed scheme are independent on the total number of time periods in the scheme. When compared with the existing FS-PKE scheme, our proposed scheme is much more efficient and practical. We also discuss how our scheme achieves chosen ciphertext security in the standard model and in the random oracle model respectively.