On the Concrete Security of Goldreich’s Pseudorandom Generator

International audienceLocal pseudorandom generators allow to expand a short random string into a long pseudo-random string, such that each output bit depends on a constant number d of input bits. Due to its extreme efficiency features, this intriguing primitive enjoys a wide variety of applications in cryptography and complexity. In the polynomial regime, where the seed is of size n and the output of size n s for s > 1, the only known solution, commonly known as Goldreich's PRG, proceeds by applying a simple d-ary predicate to public random sized subsets of the bits of the seed. While the security of Goldreich's PRG has been thoroughly investigated, with a variety of results deriving provable security guarantees against class of attacks in some parameter regimes and necessary criteria to be satisfied by the underlying predicate, little is known about its concrete security and efficiency. Motivated by its numerous theoretical applications and the hope of getting practical instantiations for some of them, we initiate a study of the concrete security of Goldreich's PRG, and evaluate its resistance to cryptanalytic attacks. Along the way, we develop a new guess-and-determine-style attack, and identify new criteria which refine existing criteria and capture the security guarantees of candidate local PRGs in a more fine-grained way

Stable isotopic signatures for hydrogeochemical characterisation of ground water from Pondicherry to Nagapattinam, Tamil Nadu

© Capital Publishing Company 2015.Groundwater recharge is a critical hydrological parameter. Identification of recharge zones and recharge estimates are essential to water resources management (Scanlon and Cook, 2002; Raju et al., 2006). In recent years, the overgrowing population and climate change are putting water resources under pressure all over the world. Sustainable management of aquifers to meet human and ecosystem needs will require protection of recharge areas and their augmentation (Reddy et al., 2000)