Pape, S.In Financial Cryptography and Data Security - 18th International Conference, FC 2014, Christ Church, Barbados, March 3-7, 2014, Revised Selected Papers, pages 291-303, 2014, Acceptance rate: 31 / 138 = 22.5%.
In some scenarios, especially when visual cryptography is used, the attacker has no access to an encryption oracle, and thus is not able to mount chosen-plaintext attacks. Based on the notion of real-or-random security under chosen-plaintext attacks (ROR-CPA) given by Bellare et al., we propose the notion of sample-or-random security under ciphertext-only attacks (SOR-CO). We prove that the notion of SOR-CO is fundamentally weaker than the notion of ROR-CPA security and demonstrate the usefulness of our notion by applying it to segment-based visual cryptography. An additional contribution of this paper is the construction of a new segment-based visual encryption scheme with noise based on work by Doberitz. To our knowledge, this is the first visual encryption scheme which makes use of noise. We conjecture that it is secure in the sense of SOR-CO security if the key is not used too often and if the encryption schemes security parameters are chosen accordingly.