Researcher Eric Lu Breaks Record by Factoring RSA-260 Without AI Assistance

Early Thursday, Eric Lu of the AI startup Cognition announced he had found a 130-digit factor that divides RSA-260, the largest RSA challenge ever solved. RSA numbers were published in 1991 as a test of factoring difficulty, with RSA-250 factored in 2020 after months of massive sieving across many machines. Lu says his approach involved manual prime sampling with limited computer help, and he offered little detail beyond a tongue-in-cheek remark about “good old paper and pencil.”

Fellow researcher Emmanuele Thomé estimates RSA-260 to be roughly three times harder than RSA-250, suggesting a multi-month effort. While the achievement demonstrates progress, the primes used in practical RSA encryption are much larger—typically over two thousand binary bits—so current online security remains intact. Experts point to quantum computing as the more plausible future threat to RSA, as classical factoring, even with clever tricks, stays computationally prohibitive. Nonetheless, the breakthrough highlights ongoing interest in cryptographic challenges and the ingenuity of individual researchers.