Welcome to the resource topic for 2011/226
Title:
Substitution-permutation networks, pseudorandom functions, and Natural Proofs
Authors: Eric Miles, Emanuele Viola
Abstract:This paper takes a new step towards closing the troubling gap between pseudorandom functions (PRF) and their popular, bounded-input-length counterparts. This gap is both quantitative, because these counterparts are more efficient than PRF in various ways, and methodological, because these counterparts usually fit in the substitution-permutation network paradigm (SPN) which has not been used to construct PRF. We give several candidate PRF F_i that are inspired by the SPN paradigm. This paradigm involves a substitution function'' (S-box). Our main candidates are: 1. F_1 : {0,1}^n -> {0,1}^n is an SPN whose S-box is a random function on b bits, given as part of the seed. We prove unconditionally that F_1 resists attacks that run in time at most 2^{Omega(b)}. Setting b = omega(log n) we obtain an inefficient PRF, which however seems to be the first such construction using the SPN paradigm. 2. F_2 : {0,1}^n -> {0,1}^n is an SPN where the S-box is (patched) field inversion, a common choice in practical constructions. F_2 is computable with Boolean circuits of size n * log^{O(1)} n, and in particular with seed length n * log^{O(1)} n. We prove that this candidate has exponential security 2^{Omega(n)} against linear and differential cryptanalysis. 3. F_3 : {0,1}^n -> {0,1} is a non-standard variant on the SPN paradigm, where states’’ grow in length. F_3 is computable with size n^{1+eps}, for any eps > 0, in the restricted circuit class TC0 of unbounded fan-in majority circuits of constant-depth. We prove that F_3 is almost 3-wise independent. 4. F_4 : {0,1}^n → {0,1} uses an extreme setting of the SPN parameters (one round, one S-box, no diffusion matrix). The S-box is again (patched) field inversion. We prove that this candidate is a small-bias generator (for tests of weight up to 2^{0.9n}). Assuming the security of our candidates, our work also narrows the gap between the ``Natural Proofs barrier’’ [Razborov & Rudich; JCSS '97] and existing lower bounds, in three models: unbounded-depth circuits, TC0 circuits, and Turing machines. In particular, the efficiency of the circuits computing F_3 is related to a result by Allender and Koucky [JACM '10] who show that a lower bound for such circuits would imply a lower bound for TC0.
ePrint: https://eprint.iacr.org/2011/226
Talk: https://www.youtube.com/watch?v=8YQw8g6Uwd8
Slides: https://iacr.org/cryptodb/archive/2012/CRYPTO/presentation/1-5-Miles.pdf
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