Sophie Germain

M. LeBlanc and Safe Primes

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Sophie Germain (born 1776 in Paris) was a French mathematician and who used safe primes to investigate Fermat’s Last Theorem. She gained her knowledge of mathematics by studying the works of Euler and communicated her ideas with other famous mathematics scholars including Legendre, Fourier and Gauss.

In fact, at the time, she faced great resistance in her studies, including from her parent who tried to stall her research by confiscating her candles and taking away her clothes. Sophie also hid her gender when communicating with Gauss and used the pseudonym of M. LeBlanc. But, against all the obstacles she faced, she overcame them and even learnt Greek and Latin so that she could read about the works of Euler and Newton.

Sophie Germain prime

A Sophie Germain prime (p) is a prime number which also generates a prime at 2p + 1. Thus 11 is a Sophie Germain prime, and where 23 is a safe prime. But 17 is not a Sophie Germain prime, as we get 35 (2x17+1), and which can be factorized. These primes have been seen as being important when selecting prime numbers to be used in the RSA method. For this, we create a public modulus (N) and which is the multiplication of two large prime numbers (p and q). If these prime numbers are weak, it can make the factorization of N easier.

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Prof Bill Buchanan OBE FRSE
ASecuritySite: When Bob Met Alice

Professor of Cryptography. Serial innovator. Believer in fairness, justice & freedom. Based in Edinburgh. Old World Breaker. New World Creator. Building trust.