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Constructing Variable-Length PRPs and SPRPs from Fixed-Length PRPs

Cook, Debra L.; Yung, Moti; Keromytis, Angelos D.

We create variable-length pseudorandom permutations (PRPs) and strong PRPs (SPRPs) accepting any input length chosen from the range of b to 2b bits from fixed-length, b-bit PRPs. We utilize the elastic network that underlies the recently introduced concrete design of elastic block ciphers, exploiting it as a network of PRPs. We prove that three and four-round elastic networks are variable-length PRPs and five-round elastic networks are variable-length SPRPs, accepting any input length that is fixed in the range of b to 2b bits, when the round functions are independently chosen fixed-length PRPs on b bits. We also prove that these are the minimum number of rounds required.

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Title
Information Security and Cryptology: 4th International Conference, Inscrypt 2008, Beijing, China, December 14-17, 2008: Revised Selected Papers
Publisher
Springer
DOI
https://doi.org/10.1007/978-3-642-01440-6_14

More About This Work

Academic Units
Computer Science
Series
Lecture Notes in Computer Science, 5487
Published Here
March 9, 2012