Dimitar Jetchev

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We prove that if one can predict any of the bits of the input to an elliptic curve based one-way function over a finite field, then we can invert the function. In particular, our result implies that if one can predict any of the bits of the input to a classical pairing-based one-way function with non-negligible advantage over a random guess then one can(More)
We present a new construction of a compression function H : {0, 1} → {0, 1} that uses two parallel calls to an ideal primitive (an ideal blockcipher or a public random function) from 2n to n bits. This is similar to the well-known MDC-2 or the recently proposed MJH by Lee and Stam (CT-RSA’11). However, unlike these constructions, we show already in the(More)
We study the security of elliptic curve Diffie-Hellman secret keys in the presence of oracles that provide partial information on the value of the key. Unlike the corresponding problem for finite fields, little is known about this problem, and in the case of elliptic curves the difficulty of representing large point multiplications in an algebraic manner(More)
We show that the least significant bits (LSB) of the elliptic curve Diffie–Hellman secret keys are hardcore. More precisely, we prove that if one can efficiently predict the LSB with non-negligible advantage on a polynomial fraction of all the curves defined over a given finite field Fp, then with polynomial factor overhead, one can compute the entire(More)
Consider a joint distribution (X,A) on a set X ×{0, 1}. We show that for any family F of distinguishers f : X × {0, 1} → {0, 1}, there exists a simulator h : X → {0, 1} such that 1. no function in F can distinguish (X,A) from (X,h(X)) with advantage ǫ, 2. h is only O(2ǫ) times less efficient than the functions in F . For the most interesting settings of the(More)
We study visibility of Shafarevich–Tate groups of modular abelian varieties in Jacobians of modular curves of higher level. We prove a theorem about the existence of visible elements at a specific higher level under certain hypothesis which can be verified explicitly. We also provide a table of examples of visible subgroups at higher level and state a(More)
Kolyvagin used Heegner points to associate a system of cohomology classes to an elliptic curve over Q and conjectured that the system contains a non-trivial class. His conjecture has profound implications on the structure of Selmer groups. We provide new computational and theoretical evidence for Kolyvagin’s conjecture. More precisely, we explicitly compute(More)