Engineer Cracks RSA-260 After 35 Years; 2048-Bit Keys Still Safe

Eric Lu, an engineer at Cognition, says he has factored RSA-260, the 260-digit (862-bit) semiprime from RSA Security’s 1991 factoring challenge that had stood unbroken for 35 years. He announced it on September 3, 2026 with a single terse X post: one of the number’s two 130-digit prime factors, followed by the words “divides RSA-260.” The claim checks out — the two 130-digit primes multiply back to the exact 260-digit composite, so this is a real result, not a stunt.

The milestone unseats RSA-250 (829 bits, cracked by an academic team in 2020) as the largest number factored with a general-purpose algorithm. What stands out is the shape of the effort: rather than a large university consortium burning through a supercomputing grant, this was reportedly a months-long individual push. The method has not been disclosed and no write-up has been published, leaving open whether Lu ran the standard General Number Field Sieve at scale or leaned on something less conventional — the most interesting open question here.

For anyone relying on modern encryption, the practical impact is essentially zero. At 862 bits, RSA-260 offers only about 74 bits of security; today’s baseline is 2048-bit keys, which are astronomically harder to factor. This is a marker of steady progress in computational number theory and a data point for cryptographers tracking how fast the frontier moves, not a break of anything running in production. The undisclosed technique is the detail worth watching as details emerge.