| New paradigms for constructing symmetric encryption schemes secure against chosen ciphertext attack (2000) | |||||||||||||||||
Abstract | |||||||||||||||||
| Abstract. The paradigms currently used to realize symmetric encryption schemes secure against adaptive chosen ciphertext attack (CCA) try to make it infeasible for an attacker to forge “valid ” ciphertexts. This is achieved by either encoding the plaintext with some redundancy before encrypting or by appending a MAC to the ciphertext. We suggest schemes which are provably secure against CCA, and yet every string is a “valid ” ciphertext. Consequently, our schemes have a smaller ciphertext expansion than any other scheme known to be secure against CCA. Our most efficient scheme is based on a novel use of “variable-length ” pseudorandom functions and can be efficiently implemented using block ciphers. We relate the difficulty of breaking our schemes to that of breaking the underlying primitives in a precise and quantitative way. 1 | |||||||||||||||||
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