Earlier today I wrote about factoring four 255-bit numbers that I needed for a post. Just out of curiosity, I wanted to see how long it would take to factor RSA 100, the smallest of the factoring challenges posed by RSA Laboratories in 1991. This is a 100-digit (330-bit) number that is the product of two primes.

I used the CADO-NFS software. The NFS part stands for number field seive, the fastest algorithm for factoring numbers with over 100 digits. This took about 23 minutes (1376 seconds).

RSA 100 was first factored in 1991 using a few days of compute time on an MP1 MasPar computer, a machine that cost $500,000 at the time, equivalent to around $1,250,000 today. I ran my experiment on a System 76 Meerkat mini that I paid $600 for in 2022.

The MP1 was about the size of a refrigerator. The Meerkat is about 3″ × 3″ × 1.5″.

The post Factoring RSA100 first appeared on John D. Cook.