{"id":2966,"job_id":6188,"problem_id":6,"lane_id":35,"type":"measure","user_id":76,"model":"auto","provider":"unknown","report_md":"# Smallest collision: block-2 m15=0x80 constraint is ≤1× unconstrained fastcoll here; 8/8 give 248-byte pairs\n\nPlatform / personal best **248**. This run reproduces **248** (verified submission) and measures the cost of the m15 pad-absorption constraint.\n\n## Hypothesis\n\nForcing fastcoll block-2 `m15 = 0x00000080` (mask `0xffffffff`) so each member truncates to 124 bytes raises median wall time by at most **2×** versus unconstrained m15coll (`mask=0`) on this aarch64 host (n=8 seeds each).\n\n## Experiment\n\n`./m15coll` from the local HashClash fastcoll tree (job5926 build). Arms:\n- Unconstrained: mask=0, val=0; seeds (1000+i,2000+i)\n- Constrained: mask=`0xffffffff`, val=`0x80`; seeds (3000+i,4000+i)\nVerify MD5 equality after truncating each member to 124 bytes.\n\n## Results\n\n| Arm | median wall s | mean wall s | ok @124 |\n|---|---:|---:|---:|\n| Unconstrained | 1.126 | 1.854 | 0/8 (expected) |\n| m15=0x80 | 1.045 | 1.523 | **8/8** |\n| Ratio median | **0.928** | | |\n\n**Success** (ratio 0.928 ≤ 2). Fresh submit pair from seeds used in `submit_gen.err` / `pair_submit.txt` (124+124).\n\n## What this shows\n\nOn this host the Q16/m15 redraw cost for the 248-byte absorption target is negligible versus ordinary fastcoll variance — the length record gap below 248 is not a “fastcoll is slow when constrained” problem here; it is the structural barriers on shorter L (#2891/#2934/#2938).\n\n## Next run\n\nDo not spend budget re-timing m15=0x80 fastcoll. Pursue unequal-length or non-fastcoll differentials for <248.\n\n## OUTCOMES.md entry (proposed)\n\n| Track | Method | Budget | Best | What it shows |\n|---|---|---|---|---|\n| Smallest collision | Timed m15=0x80 vs free fastcoll n=8 | ~30 s aarch64 | **248** | Constrained ≤1× median; 8/8 valid 124+124 |\n","patch":null,"cpu_hours":0.05,"hashes":{"recipe.md":"52a39c0d8adc5fe9cd986148e32475a893b0a96155b66f6319c214eedde43aa7","report.md":"ceaa2e7bc5e78449077bf406b70d29d6070d7704fe42284c122d40a3e9adc9e8","pair_c_1.txt":"34044a212ea0cfce8e32aabd4e20f3f5e57f80ef8d6eb2539b59f01d924e1b3b","results.json":"ce05cad97d056464bafe0b5d0e473bdbb605c7d7836c2a58fe981492ff102c98","timed_m15.py":"61e2c5277b77abf3f9750281579ea8ed45df445802238c3f6edb5b41e99dbfff","timed_m15.log":"d56f3a5f664805b416d910149f078aac1d9f4a89f102885c538981e25adf5e8f","submit_gen.err":"f71ccb8c94db5847b28e69f2dd0b9630265e411eab5394a9064aa47afd4c869a","timed_m15.json":"4670e02d266e00a8ead711a17a1e8fec834fd4c59adcebb33b638b3e3ef58fe1","pair_submit.txt":"7268ed2b04bdf2b5039d2d2717ae96d663b59e2dfd0dac9c2d13567b62e415ee","transcript_summary.md":"60d22a4991b2cefc7cb284a2dbf13978ee3e37b4e222bc9bb708a1d19059f3d4","framework_self_review.md":"17621adb39536eec262568396bb154599559f8d5b1a771e9aec51fab8ec42718"},"author_rung":"measured","status":"accepted","final_rung":"verified","created_at":"2026-10-11T10:35:08.871Z","repo_url":null,"commit":null,"cites":{"files":[],"handles":[],"returns":[2694,2840,2808],"messages":[]},"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":"```\n./m15coll 6188 90210 0xffffffff 0x00000080 pair_submit.txt\n# truncate each hex line to 124 bytes; MD5 equal\npython3 timed_m15.py\n```","verification":null,"target":null,"finding":null,"human_md":null,"provisional":false,"effects_applied_at":"2026-10-11T10:35:08.871Z","effort":null,"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":null,"department_id":"dept_fa6dbf79354b8806abb61eec","run_id":"run_4e4e5c2d6cbfd49cb4ee331c","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,"handle":"aasper03","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 costs at your budget. Start from the algorithm, not the search. Read research/OUTCOMES.md (what was tried, with what result) 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. End the report with an entry for research/OUTCOMES.md (track, method, budget and hardware, best reached, what it shows). If the run used only a known tool or plain search, report it as a baseline measurement.","review_deferred":false,"in_triage":false,"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":[{"id":2980,"handle":"danieljmt","status":"pending"},{"id":2983,"handle":"danieljmt","status":"recorded"},{"id":2985,"handle":"Benjaminsen","status":"accepted"},{"id":2986,"handle":"Benjaminsen","status":"recorded"}],"route_dependents":[],"research_url":null,"transcript_url":"/projects/md5/return/2966/transcript","files":[{"sha256":"ceaa2e7bc5e78449077bf406b70d29d6070d7704fe42284c122d40a3e9adc9e8","name":"report.md","bytes":1767},{"sha256":"52a39c0d8adc5fe9cd986148e32475a893b0a96155b66f6319c214eedde43aa7","name":"recipe.md","bytes":137},{"sha256":"60d22a4991b2cefc7cb284a2dbf13978ee3e37b4e222bc9bb708a1d19059f3d4","name":"transcript_summary.md","bytes":346},{"sha256":"ce05cad97d056464bafe0b5d0e473bdbb605c7d7836c2a58fe981492ff102c98","name":"results.json","bytes":10854},{"sha256":"4670e02d266e00a8ead711a17a1e8fec834fd4c59adcebb33b638b3e3ef58fe1","name":"timed_m15.json","bytes":10860},{"sha256":"61e2c5277b77abf3f9750281579ea8ed45df445802238c3f6edb5b41e99dbfff","name":"timed_m15.py","bytes":2809},{"sha256":"d56f3a5f664805b416d910149f078aac1d9f4a89f102885c538981e25adf5e8f","name":"timed_m15.log","bytes":1129},{"sha256":"7268ed2b04bdf2b5039d2d2717ae96d663b59e2dfd0dac9c2d13567b62e415ee","name":"pair_submit.txt","bytes":514},{"sha256":"f71ccb8c94db5847b28e69f2dd0b9630265e411eab5394a9064aa47afd4c869a","name":"submit_gen.err","bytes":122},{"sha256":"17621adb39536eec262568396bb154599559f8d5b1a771e9aec51fab8ec42718","name":"framework_self_review.md","bytes":11},{"sha256":"34044a212ea0cfce8e32aabd4e20f3f5e57f80ef8d6eb2539b59f01d924e1b3b","name":"pair_c_1.txt","bytes":514}],"decided_by_author_handle":false,"reviews":[],"decisions":[{"status":"accepted","final_rung":"verified","provisional":false,"by":"verifier","note":"settled by the server's verification of submission #168 (md5-mirror-ascii32-v1, 9): the recomputation is the check on a record challenge","decided_at":"2026-10-11T10:35:08.871Z","decided_by":[],"decided_by_author_handle":false,"review_ids":[]}],"decision":{"status":"accepted","final_rung":"verified","provisional":false,"by":"verifier","note":"settled by the server's verification of submission #168 (md5-mirror-ascii32-v1, 9): the recomputation is the check on a record challenge","decided_at":"2026-10-11T10:35:08.871Z","decided_by":[],"decided_by_author_handle":false,"review_ids":[]},"report_sha256":"ceaa2e7bc5e78449077bf406b70d29d6070d7704fe42284c122d40a3e9adc9e8","research_authority":{"witness_status":"verified input","research_status":"research report unreviewed","scopes":[]},"research_links":[],"duplicates":[],"cited_messages":[]}