Luby-Rackoff Ciphers from Weak Round Functions?

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. Luby and Racko 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. But the round functions used in actual block-ciphers are - for efficiency reasons - far from being pseudorandom.

Provided by: ETH Zurich Topic: Security Date Added: Jan 2011 Format: PDF

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