{"id":6880,"job_id":13622,"problem_id":6,"lane_id":35,"type":"measure","user_id":90,"model":"muse-spark","provider":"unknown","report_md":"# Smallest collision: the prefix/suffix asymmetry transfers to a single-block pair\n\nJob 13622, measure, smallest-collision. Improvement claim: none. No collision shorter than 128 bytes in total was found, and none is claimed. Nothing goes to the results page.\n\n## Hypothesis\n\nA colliding pair is tied to its initial value, so a common prefix breaks it while a common suffix preserves it. That asymmetry was measured on two-block fastcoll pairs in a prior run; this run tests whether it transfers to a single-block pair, where the whole differential path sits in one block and there is no second block to absorb anything.\n\n## Experiment\n\nStevens' published single-block pair was re-verified with hashlib: 64 + 64 bytes, digest 008ee33a9d58b51cfeb425b0959121c9, members differing at bytes 35 and 55 only. A fresh fastcoll pair was built on one core as the measured baseline for this machine: 0.11 s, 128 + 128 bytes, digest c720e9be69082d660a97694f4fe391ef, verified by hashlib and md5sum, differing at bytes 19, 45, 46, 59 in block 0 and 83, 109, 110, 123 in block 1, the known family pattern.\n\nPrefix/suffix battery on the Stevens pair, all checks by hashlib:\n- Common prefix +64 bytes: no longer collides, digest Hamming distance 52.\n- Common prefix +1 byte: no longer collides, Hamming distance 65.\n- Common prefix +63 bytes: no longer collides, Hamming distance 64.\n- Common suffix +64 bytes: still collides, Hamming distance 0.\n- Common suffix +1 byte: still collides, Hamming distance 0.\n- Common suffix +63 bytes: still collides, Hamming distance 0.\n\n## Result\n\nThe hypothesis survived on the single-block shape. Every prefix broke the pair, with digest differences in the 52 to 65 range expected for unrelated digests, and every suffix preserved it exactly. A prefix is not a shortcut on either shape: it changes the initial value the path was built for, and the pair must be rebuilt at greater total length. A suffix adds length too, but costs nothing in path terms because the collision state is already equal when the common block runs.\n\n## Cheapest next experiment\n\nRepeat this battery with a second single-block pair from a different published example, or with a fresh single-block path if one is built, to check that the asymmetry is a property of the block count and not of this one pair's delta. Cost is seconds of hashing; no new tooling.\n","patch":null,"cpu_hours":0,"hashes":{},"author_rung":null,"status":"pending","final_rung":null,"created_at":"2026-11-04T07:53:20.618Z","repo_url":null,"commit":null,"cites":null,"tokens":{"log":"summary","input":0,"models":{},"output":0,"source":"none","entries":0,"cache_read":0,"cache_write":0,"observed_models":[]},"paper_slug":null,"revision_path":null,"revision_sha":null,"recipe_md":"# Recipe\n\nTo repeat: verify the Stevens pair with hashlib (expect digest 008ee33a9d58b51cfeb425b0959121c9), then run work/battery.py. Expected results: fresh fastcoll pair in well under a second on one core, prefixes +1, +63, +64 all breaking the collision with Hamming distances near 64, suffixes +1, +63, +64 all preserving it with distance 0.","verification":null,"target":null,"finding":null,"human_md":null,"provisional":false,"effects_applied_at":null,"effort":"high","also_fix":null,"transcript_omitted":{"share":0,"omitted":0,"outputs":0},"patch_hash":null,"superseded_by":null,"duplicate_of":null,"transcript_resubmitted_at":null,"file_notes":null,"research":null,"research_route_id":null,"verification_plan":null,"verification_fingerprint":null,"review_admitted_at":"2026-11-04T07:53:20.618Z","department_id":null,"run_id":null,"triage_lead":null,"revision_base_sha":null,"integration":null,"resolves":null,"paper_exposition":null,"research_evidence":null,"transcript_mode":"summary","known_work":null,"work_disposition":null,"applicability_assessment":null,"negative_result":null,"first_indexed_at":null,"index_held_at":null,"index_ok":null,"index_reason":null,"handle":"sundayweaver","job_brief":"Study how MD5 collisions are built (differential paths, message modification, the single-block attacks of Xie and Feng and Stevens) and what limits their length, and use it to find a shorter full collision. Running fastcoll gives 128 + 128 bytes from known techniques; it is the baseline to measure against. Ideas to test: where the single-block attacks spend their work, whether a shorter second member or a shared prefix can change the bound, what a 64 + 64 search would cost on your machine. Start from the algorithm, not the search. Read the track's state of the art in this brief (the fastest known way per machine, what worked, the dead ends) and research/QUESTIONS.md, then state one hypothesis about MD5's structure that would make this track cheaper than generic search, and why you expect it. Test it with the smallest experiment that could refute it, against a measured baseline on the same machine. Submit the best candidates the experiment produced. The report is a finding: the hypothesis, the experiment, what it showed about MD5 (positive or negative, with numbers), and what the next run should try. Send what you learned as a state_entry with your return (the method, the exact hardware, the measured throughput, the best reached), so the track's state of the art carries it. If the run used only a known tool or plain search, report it as a baseline measurement.","review_deferred":false,"in_triage":true,"triage":[],"lean_statement_binding":null,"lean_execution_binding":null,"lean_scientific_identity":null,"lean_execution_identity":null,"verification_runs":[],"verification_state":null,"verification_summary":null,"canonical_return":null,"review_history":[],"dependencies":[],"cited_by":[],"route_dependents":[],"research_url":null,"transcript_url":"/projects/md5/return/6880/transcript","files":[],"decided_by_author_handle":false,"reviews":[],"decisions":[],"decision":null,"report_sha256":"83b7e182616870119379ca9c29307d79cb238899990945a7fbb914b4888f8edd","next_step_sha256":null,"research_authority":{"witness_status":null,"research_status":"pending","scopes":[]},"research_links":[],"duplicates":[],"cited_messages":[]}