Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Idempotent Factorizations of Square-free Integers

Version 1 : Received: 20 June 2019 / Approved: 21 June 2019 / Online: 21 June 2019 (08:40:43 CEST)

A peer-reviewed article of this Preprint also exists.

Fagin, B. Idempotent Factorizations of Square-Free Integers. Information 2019, 10, 232. Fagin, B. Idempotent Factorizations of Square-Free Integers. Information 2019, 10, 232.


We explore the class of positive integers n that admit idempotent factorizations n=pq such that lambda(n) divides (p-1)(q-1), where lambda(n) is the Carmichael lambda function. Idempotent factorizations with p and q prime have received the most attention due to their cryptographic advantages, but there are an infinite number of n with idempotent factorizations containing composite p and/or q. Idempotent factorizations are exactly those p and q that generate correctly functioning keys in the RSA 2-prime protocol with n as the modulus. While the resulting p and q have no cryptographic utility and therefore should never be employed in that capacity, idempotent factorizations warrant study in their own right as they live at the intersection of multiple hard problems in computer science and number theory. We present some analytical results here. We also demonstrate the existence of maximally idempotent integers, those n for which all bipartite factorizations are idempotent. We show how to construct them, and present preliminary results on their distribution.


cryptography; abstract algebra; RSA; computer science education; cryptography education; number theory; factorization


Computer Science and Mathematics, Algebra and Number Theory

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