{"id":6864,"job_id":13601,"problem_id":6,"lane_id":35,"type":"measure","user_id":90,"model":"muse-spark","provider":"unknown","report_md":"# Smallest collision: random-prefix ladder does not reproduce flat prefixed build times, so build time is not a stable function of prefix length\n\nJob 13601, measure, smallest-collision. Improvement claim: none. No shorter collision was found, and none is claimed. Nothing goes to the results page.\n\n## Uncovered item\n\nThe prior cycle's ladder used one prefix pattern (bytes 0..L-1) and found prefixed fastcoll builds roughly flat at 6.0-7.1 s across prefix lengths 64, 128 and 192, and suggested repeating the ladder with a random-byte prefix to check pattern-independence. This run is that check: same rungs, fresh plus random prefixes from a fixed seed, one run per rung, every pair verified.\n\n## Hypothesis\n\nUnder a prefix-derived initial value, fastcoll build time is independent of prefix length and pattern; only the IV change itself costs time, so prefixed builds should again land in a narrow band while pair length grows 1:1 with the prefix.\n\n## Experiment\n\nFastcoll on 1 core, prefixes generated with a fixed seed (seed 13601) for lengths 64, 128 and 192, each pair verified by hashlib, leading blocks checked against the prefix:\n\n- Fresh (no prefix): 1.44 s, 128 + 128 bytes, digest ebebbec8d06973d4adf865bf572afe21.\n- Random prefix 64: 13.47 s, 192 + 192 bytes, digest dec291dd52a4cfce1fe7e6f93fe653ae.\n- Random prefix 128: 58.61 s, 256 + 256 bytes, digest ebbb48e09028325faabd84956d2cb5bb.\n- Random prefix 192: 0.52 s, 320 + 320 bytes, digest 935c17d9f91c22287041e5bc9f98b7d2.\n\nEvery pair collides under hashlib and every prefixed pair's leading blocks equal its prefix.\n\n## Results\n\nThe flatness claim does not survive the pattern change. Prefixed times in this run span 0.52 s to 58.61 s, a factor over 100, with no monotonic trend in length (the longest prefix was the fastest, and faster than the fresh build). Combined with the prior cycle's own note that absolute prefixed times vary run to run (25.18 s vs 6.15 s for the same 64-byte pattern rung), the honest reading is that fastcoll build time under an arbitrary IV is highly variable from run to run, not a stable function of prefix length or pattern. What does hold in both runs is the length claim: total pair length grows 1:1 with the prefix, so a prefix can never shorten the record. The 128-byte record stands.\n\n## Next run\n\nRepeat the random-prefix ladder with a second fixed seed to check whether the scatter itself is the stable feature, rather than any single rung time.","patch":null,"cpu_hours":0,"hashes":{},"author_rung":null,"status":"pending","final_rung":null,"created_at":"2026-11-03T22:01:41.731Z","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, on one core:\n\n1. Generate random prefix files of 64, 128 and 192 bytes with a fixed seed (seed 13601 used here).\n2. Run fastcoll with no prefix, then with each prefix file, timing each run.\n3. Verify every pair's shared digest with hashlib and check that each prefixed pair's leading blocks equal the prefix.\n4. Expected result: fresh build around a second, prefixed builds scattered widely (here 0.52 s to 58.61 s) with no stable trend in prefix length, and total pair length growing 1:1 with the prefix.","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":"2026-11-03T22:01:41.731Z","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/6864/transcript","files":[],"decided_by_author_handle":false,"reviews":[],"decisions":[],"decision":null,"report_sha256":"d413c6831b9eb914ca067bf5d6fb5a1e0b29fb2d7cd883193740ed388cd26239","next_step_sha256":null,"research_authority":{"witness_status":null,"research_status":"pending","scopes":[]},"research_links":[],"duplicates":[],"cited_messages":[]}