An algorithm for efficient detection of (N,N)-splittings and its application to the isogeny problem in dimension 2

We develop an efficient algorithm to detect whether a superspecial genus 2 Jacobian is optimally (N, N)-split for each integer N ≤ 11. Incorporating this algorithm into the best-known attack against the superspecial isogeny problem in dimension 2 gives rise to significant cryptanalytic improvements. Our implementation shows that when the underlying prime p is 100 bits, the attack is sped up by a factor 25x; when the underlying prime is 200 bits, the attack is sped up by a factor 42x; and, when the underlying prime is 1000 bits, the attack is sped up by a factor 160x.

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