{"acknowledgement":"Most of this work was done while the K. Pietrzak was a PhD student at ETH where he was supported by the Swiss National Science Foundation, project No. 200020- 103847/1. Currently he is partially supported by the Commission of the European Communities through the IST program under contract IST-2002-507932 ECRYPT.","citation":{"ieee":"U. Maurer, Y. Oswald, K. Z. Pietrzak, and J. Sjödin, “Luby Rackoff ciphers from weak round functions ,” presented at the EUROCRYPT: Theory and Applications of Cryptographic Techniques, 2006, vol. 4004, pp. 391–408.","short":"U. Maurer, Y. Oswald, K.Z. Pietrzak, J. Sjödin, in:, Springer, 2006, pp. 391–408.","ama":"Maurer U, Oswald Y, Pietrzak KZ, Sjödin J. Luby Rackoff ciphers from weak round functions . In: Vol 4004. Springer; 2006:391-408. doi:<a href=\"https://doi.org/10.1007/11761679_24\">10.1007/11761679_24</a>","mla":"Maurer, Ueli, et al. <i>Luby Rackoff Ciphers from Weak Round Functions </i>. Vol. 4004, Springer, 2006, pp. 391–408, doi:<a href=\"https://doi.org/10.1007/11761679_24\">10.1007/11761679_24</a>.","apa":"Maurer, U., Oswald, Y., Pietrzak, K. Z., &#38; Sjödin, J. (2006). Luby Rackoff ciphers from weak round functions  (Vol. 4004, pp. 391–408). Presented at the EUROCRYPT: Theory and Applications of Cryptographic Techniques, Springer. <a href=\"https://doi.org/10.1007/11761679_24\">https://doi.org/10.1007/11761679_24</a>","chicago":"Maurer, Ueli, Yvonne Oswald, Krzysztof Z Pietrzak, and Johan Sjödin. “Luby Rackoff Ciphers from Weak Round Functions ,” 4004:391–408. Springer, 2006. <a href=\"https://doi.org/10.1007/11761679_24\">https://doi.org/10.1007/11761679_24</a>.","ista":"Maurer U, Oswald Y, Pietrzak KZ, Sjödin J. 2006. Luby Rackoff ciphers from weak round functions . EUROCRYPT: Theory and Applications of Cryptographic Techniques, LNCS, vol. 4004, 391–408."},"month":"07","date_created":"2018-12-11T12:02:03Z","status":"public","year":"2006","publisher":"Springer","page":"391 - 408","day":"11","date_published":"2006-07-11T00:00:00Z","publist_id":"3465","date_updated":"2021-01-12T07:41:51Z","volume":4004,"extern":1,"type":"conference","intvolume":"      4004","_id":"3214","author":[{"last_name":"Maurer","full_name":"Maurer, Ueli M","first_name":"Ueli"},{"last_name":"Oswald","full_name":"Oswald, Yvonne A","first_name":"Yvonne"},{"id":"3E04A7AA-F248-11E8-B48F-1D18A9856A87","last_name":"Pietrzak","orcid":"0000-0002-9139-1654","full_name":"Krzysztof Pietrzak","first_name":"Krzysztof Z"},{"full_name":"Sjödin,  Johan","first_name":"Johan","last_name":"Sjödin"}],"doi":"10.1007/11761679_24","conference":{"name":"EUROCRYPT: Theory and Applications of Cryptographic Techniques"},"quality_controlled":0,"alternative_title":["LNCS"],"title":"Luby Rackoff ciphers from weak round functions ","publication_status":"published","abstract":[{"lang":"eng","text":"The Feistel-network is a popular structure underlying many block-ciphers where the cipher is constructed from many simpler rounds, each defined by some function which is derived from the secret key.\nLuby and Rackoff showed that the three-round Feistel-network – each round instantiated with a pseudorandom function secure against adaptive chosen plaintext attacks (CPA) – is a CPA secure pseudorandom permutation, thus giving some confidence in the soundness of using a Feistel-network to design block-ciphers.\nBut the round functions used in actual block-ciphers are – for efficiency reasons – far from being pseudorandom. We investigate the security of the Feistel-network against CPA distinguishers when the only security guarantee we have for the round functions is that they are secure against non-adaptive chosen plaintext attacks (nCPA). We show that in the information-theoretic setting, four rounds with nCPA secure round functions are sufficient (and necessary) to get a CPA secure permutation. Unfortunately, this result does not translate into the more interesting pseudorandom setting. In fact, under the so-called Inverse Decisional Diffie-Hellman assumption the Feistel-network with four rounds, each instantiated with a nCPA secure pseudorandom function, is in general not a CPA secure pseudorandom permutation."}]}