Luby-rackoo Backwards: Increasing Security by Making Block Ciphers Non-invertible Mihir Bellare
نویسندگان
چکیده
We argue that the invertibility of a block cipher can reduce the security of schemes that use it and a better starting point for scheme design is the non invertible analog of a block cipher that is a pseudorandom function PRF Since a block cipher may be viewed as a pseudorandom permutation we are led to investigate the reverse of the problem studied by Luby and Racko and ask how can one transform a PRP into a PRF in as security preserving a way as possible The solution we propose is data dependent re keying As an illustrative special case let E f g f g f g be the block cipher Then we can construct the PRF F from the PRP E by setting F k x E E k x x We generalize this to allow for arbitrary block and key lengths and to improve e ciency We prove strong quantitative bounds on the value of data dependent re keying in the Shannon model of an ideal cipher and take some initial steps towards an analysis in the standard model
منابع مشابه
Luby-Rackoff Backwards: Increasing Security by Making Block Ciphers Non-invertible
We argue that the invertibility of a block cipher can reduce the security of schemes that use it, and a better starting point for scheme design is the non-invertible analog of a block cipher, that is, a pseudorandom function (PRF). Since a block cipher may be viewed as a pseudorandom permutation, we are led to investigate the reverse of the problem studied by Luby and Rackoff, and ask: “how can...
متن کاملLuby-Racko Backwards: Increasing Security by Making Block Ciphers Non-Invertible
We argue that the invertibility of a block cipher can reduce the security of schemes that use it, and a better starting point for scheme design is the non-invertible analog of a block cipher, that is, a pseudorandom function (PRF). Since a block cipher may be viewed as a pseudorandom permutation, we are led to investigate the reverse of the problem studied by Luby and Racko , and ask: \how can ...
متن کاملTowards Making Luby-Rackoff Ciphers Optimal and Practical
We provide new constructions for Luby-Rackoo block ciphers which are eecient in terms of computations and key material used. Next, we show that we can make some security guarantees for Luby-Rackoo block ciphers under much weaker and more practical assumptions about the underlying function; namely, that the underlying function is a secure Message Authentication Code. Finally, we provide a SHA-1 ...
متن کاملTwo Practical and Provably Secure Block Ciphers: BEAR and LION
In this paper we suggest two new provably secure block ciphers , called BEAR and LION. They both have large block sizes, and are based on the Luby-Rackoo construction. Their underlying components are a hash function and a stream cipher, and they are provably secure in the sense that attacks which nd their keys would yield attacks on one or both of the underlying components. They also have the p...
متن کاملCryptanalysis of Ladder-DES
Feistel ciphers are very common and very important in the design and analysis of blockciphers, especially due to four reasons: (1) Many (DES-like) ciphers are based on Feistel's construction. (2) Luby and Rackoo proved the security of a four-round Feistel construction when the round functions are random. (3) Recently several provably secure ciphers were suggested, which use other (assumed secur...
متن کامل