We describe a space-efficient algorithm for solving a generalization of the subset sum problem in a finite group G, using a Pollard-rho approach. Given an element z and a sequence of elements S, our algorithm attempts to find a subsequence of S whose product in G is equal to z. For a random sequence S of length d*log2(n), where n=#G and d>=2 is a constant, we find that its expected running time is O(sqrt(n)*log(n)) group operations (we give a rigorous proof for d>4), and it only needs to store O(1) group elements. We consider applications to class groups of imaginary quadratic fields, and to finding isogenies between elliptic curves over a finite field.

Original language | English |
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Publisher | IACR |
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Number of pages | 12 |
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Publication status | Published - 2011 |
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Name | Cryptology ePrint Archive |
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Volume | 2011/004 |
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