Limits RegistryPUBLIC RECORD
Limits RegistryA team using the CADO-NFS software factored RSA-250, an 829-bit number, in February 2020 using roughly 2,700 CPU-core-years of computation on the general number field sieve, the most efficient known classical factoring algorithm for numbers of this size. It remains the largest classically factored RSA challenge semiprime as of 2026, underscoring why standards bodies now recommend RSA key sizes of at least 2,048 or 3,072 bits for long-term security.
The question, scope, and sources behind this Registry record.
A team using the CADO-NFS software factored RSA-250, an 829-bit number, in February 2020 using roughly 2,700 CPU-core-years of computation on the general number field sieve, the most efficient known classical factoring algorithm for numbers of this size. It remains the largest classically factored RSA challenge semiprime as of 2026, underscoring why standards bodies now recommend RSA key sizes of at least 2,048 or 3,072 bits for long-term security.
The bit length of RSA-250, an 829-bit (250-decimal-digit) semiprime from the RSA Factoring Challenge, factored in February 2020 using the general number field sieve — the largest RSA modulus publicly factored by classical computation as of 2026.
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Current frontiers derived from accepted Claims.
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The frontier as it changed over time.
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1 accepted Claim, with 1 linked evidence records.
Permanent ID limitsregistry.com/limits/LR-RSA250-FACTORING-RECORD
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Limits Registry. LR-RSA250-FACTORING-RECORD. Largest RSA-type number factored by classical computation. 2026.