Efficient Constructions of Variable-Input-Length Block Ciphers [chapter]

Sarvar Patel, Zulfikar Ramzan, Ganapathy S. Sundaram
2004 Lecture Notes in Computer Science  
Existing block ciphers operate on a fixed-input-length (FIL) block size (e.g., 64-bits for DES). Often, one needs a variable-inputlength (VIL) primitive that can operate on a different size input; it is, however, undesirable to construct this primitive from "scratch." This paper contains two constructions that start with a fixed-input-length block cipher and show how to securely convert it to a variable-input-length block cipher without making any additional cryptographic assumptions. Both
more » ... ructions model the FIL block cipher as a pseudorandom permutation (PRP) -that is, indistinguishable from a random permutation against adaptive chosen plaintext attack. The first construction converts it to a VIL PRP and is an efficiency improvement over the scheme of Bellare and Rogaway [4] . The second construction converts it to a VIL super pseudorandom permutation (SPRP) -that is, the resulting VIL block cipher is indistinguishable from a random permutation against adaptive chosen plaintext and ciphertext attack.
doi:10.1007/978-3-540-30564-4_23 fatcat:nba4qytunjdhldsgw4zqqbdh4e