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On the Construction of VariableInputLength Ciphers
 In Fast Software Encryption
, 1998
"... We invesitgate how to construct ciphers which operate on messages of various (and effectively arbitrary) lengths. In particular, lengths not necessarily a multiple of some block length. (By a "cipher" we mean a keyindexed family of lengthpreserving permutations, with a "good" c ..."
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We invesitgate how to construct ciphers which operate on messages of various (and effectively arbitrary) lengths. In particular, lengths not necessarily a multiple of some block length. (By a "cipher" we mean a keyindexed family of lengthpreserving permutations, with a "good" cipher being one that resembles a family of random lengthpreserving permutations.) Oddly enough, this question seems not to have been investiaged. We show how to construct variableinput length ciphers starting from any block cipher (ie, a cipher which operates on strings of some fixed length n). We do this by giving a general method starting from a particular kind of pseudorandom function and a particular kind of encryption scheme, and then we give example ways to realize these tools from a block cipher. All of our constructions are proven sound, in the provablesecurity sense of contemporary cryptography. Variableinputlength ciphers can be used to encrypt in the presence of the constraint that the ciphertex...
On the Construction of VariableInputLength Ciphers
, 1999
"... Abstract Whereas a block cipher enciphers messages of some one particular length (the blocklength), a variableinputlength cipher takes messages of varying (and preferably arbitrary) lengths. Still, the length of the ciphertext must equal the length of the plaintext. This paper introduces the probl ..."
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Abstract Whereas a block cipher enciphers messages of some one particular length (the blocklength), a variableinputlength cipher takes messages of varying (and preferably arbitrary) lengths. Still, the length of the ciphertext must equal the length of the plaintext. This paper introduces the problem of constructing such objects, and provides a practical solution. Our VIL mode of operation makes a variableinputlength cipher from any block cipher. The method is demonstrably secure in the provablesecurity sense of modern cryptography: we give a quantitative security analysis relating the difficulty of breaking the constructed (variableinputlength) cipher to the difficulty of breaking the underlying block cipher.