On the Construction of Variable-Input-Length Ciphers


Published: Feb 27, 2000 Updated: Feb 27, 2000 Section: Network Security Library :: Cryptography Author: Mihir Bellare Printable Version Adjust font size: Rating: 3/5 - 1 Votes 1 2 3 4 5

Whereas a block cipher enciphers messages of some one particular length (the blocklength), a variable-input-length 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 variable-input-length cipher from any block cipher. The method is demonstrably secure in the provable-security sense of modern cryptography: we give a quantitative security analysis relating the difficulty of breaking the constructed (variable-input-length) cipher to the difficulty of breaking the underlying block cipher.

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