A Method for Obtaining Deniable Public-Key Encryption
Maged Hamada Ibrahim · 2009
Deniable encryption is an important notion that allows a user (a sender and/or a receiver) to escape a coercion attempted by a coercive adversary. Such an adversary approaches the coerced user after transmission forcing him to reveal all his random inputs used during encryption or decryption. Since traditional encryption schemes commits the user to his random inputs, the user is forced to reveal the true values of all his random inputs (including the encrypted/decrypted messages and the encryption/decryption keys) which are verifiable by this coercer using the intercepted ciphertext. In this scenario, a coercer may force the user to perform actions against his wish. In this paper we present a scheme for senderdeniable public-key encryption, by which, the sender is able to lie about the encrypted message to a coercer and hence, escape a coercion. While the receiver is able to decrypt for the true message, the sender has the ability to open a fake message of his choice to the coercer which when verified gives the same ciphertext as the true message. Our schemes rely on quadratic residuosity of a two-prime modulus. Deniability improvements to these schemes considering the sender’s local randomness are also presented. We also show how to build an efficient deniable public-key encryption from any trapdoor permutation. Compared to the schemes proposed in [5], our schemes require much less bandwidth, provide stronger deniability and no decryption errors.