Cryptology ePrint Archive: Report 2015/526

Generic Key Recovery Attack on Feistel Scheme

Takanori Isobe and Kyoji Shibutani

Abstract: We propose new generic key recovery attacks on Feistel-type block ciphers. The proposed attack is based on the all subkeys recovery approach presented in SAC 2012, which determines all subkeys instead of the master key. This enables us to construct a key recovery attack without taking into account a key scheduling function. With our advanced techniques, we apply several key recovery attacks to Feistel-type block ciphers. For instance, we show 8-, 9- and 11-round key recovery attacks on n-bit Feistel ciphers with 2n-bit key employing random keyed F-functions, random F-functions, and SP-type F-functions, respectively. Moreover, thanks to the meet-in-the-middle approach, our attack leads to low-data complexity. To demonstrate the usefulness of our approach, we show a key recovery attack on the 8-round reduced CAST-128, which is the best attack with respect to the number of attacked rounds. Since our approach derives the lower bounds on the numbers of rounds to be secure under the single secret key setting, it can be considered that we unveil the limitation of designing an efficient block cipher by a Feistel scheme such as a low-latency cipher.

Category / Keywords: secret-key cryptography / block cipher, key scheduling function, all-subkeys-recovery attack, meet-in-themiddle attack, key recovery attack, low-data complexity attack

Original Publication (with minor differences): IACR-ASIACRYPT-2013

Date: received 1 Jun 2015

Contact author: Takanori Isobe at jp sony com

Available format(s): PDF | BibTeX Citation

Version: 20150602:061707 (All versions of this report)

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