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Prime Numbers

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338 Chapter 7 ELLIPTIC CURVE ARITHMETIC<br />

a host of elliptic-curve groups to choose from randomly, each giving a fresh<br />

chance at success.<br />

With these ideas, we may perform a heuristic complexity estimate for<br />

ECM. Suppose the number n to be factored is composite, coprime to 6, and<br />

not a proper power. Let p denote the least prime factor of n and let q denote<br />

another prime factor of n. Algorithm 7.4.2 will be successful in splitting n if<br />

we choose a, b, P in Step [Find curve ...] and if for some value of k of the form<br />

k = p a l<br />

where l ≤ π(B1) anda ≤ al, wehave<br />

<br />

i

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