Limits RegistryPUBLIC RECORD
Limits RegistryThe volunteer distributed-computing project distributed.net solved the RC5-64 challenge on 14 July 2002 after 1,757 days of searching, revealing the message 'Some things are better left unread'. Its successor, the 72-bit RC5-72 challenge, is still running and unsolved, with 256 times as many keys to search.
The question, scope, and sources behind this Registry record.
The volunteer distributed-computing project distributed.net solved the RC5-64 challenge on 14 July 2002 after 1,757 days of searching, revealing the message 'Some things are better left unread'. Its successor, the 72-bit RC5-72 challenge, is still running and unsolved, with 256 times as many keys to search.
The longest RC5 key publicly recovered by brute force in RSA Security's secret-key challenges; the 72-bit challenge remains unsolved.
Change a parameter to stress-test whether a proposed result is still inside the published specification. This is an audit aid, not a proof checker.
This record has no editable parameters. Read the formal question and assumptions before challenging it.
Current frontiers derived from accepted Claims.
An observed or demonstrated result; no opposing bound is implied.
The frontier is not sacred
Most progress starts with a disagreement that survives contact with evidence. If you can push the known lower bound up or pull the upper bound down, show us the work.
≥ when you have shown that at least this value is achievable.≤ when you have shown that anything above this value is impossible.No vibes. State the value, define the scope, and link the paper, proof, code, or reproduction that lets another person check it. Editors review every challenge before the public record changes.
Challenge this recordAssertions tied to evidence, attribution, and review.
The frontier as it changed over time.
Only accepted Claims matching the current specification contribute to the displayed bounds. Strict inequalities remain open; contradictory Claims require editorial review.
1 accepted Claim, with 1 linked evidence records.
Permanent ID limitsregistry.com/limits/LR-RC5-64-SECRET-KEY-CHALLENGE
No active verified bounties are linked to this Limit.
View verified bounty tracker ↗No accepted machine-checked reproductions are recorded for this Limit.
Limits Registry. LR-RC5-64-SECRET-KEY-CHALLENGE. Longest key broken in RSA's secret-key challenges (RC5-64). 2026.