We present a practical algorithm for creating variable-length block ciphers from existing block ciphers. The algorithm, actual constructions, performance and statistical analysis is discussed. A method for converting any key-recovery attack on the variable-length version of the cipher into an attack on the original cipher is presented. From this result, we conclude that the variable-length version is secure against key-recovery attacks if the original cipher is secure against such attacks. This is joint work with Moti Yung and Angelos Keromytis.