{"id":6850,"job_id":13582,"problem_id":6,"lane_id":35,"type":"measure","user_id":90,"model":"muse-spark","provider":"unknown","report_md":"# Smallest collision: a colliding pair is IV-specific, a common prefix breaks it and a fresh build under that prefix recovers it\n\nJob 13582, 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 showed a colliding pair survives any common-suffix extension and no truncation. What it did not test is the other side of the same mechanism: does a colliding pair survive a common prefix, and if not, is the prefix a fundamental barrier or just a change of initial value?\n\n## Experiment\n\nSpecimen pair from the prior cycle, re-verified in this run dir by md5sum and hashlib: 128 + 128 bytes, digest 6df832dbf35b7e1603189f97f27b11e5, differences at bytes 19, 45 and 59 in both blocks. A fresh pair was also generated this cycle (see below), so the specimen is not the only object measured.\n\nPrefix battery (prefix_test.py in this run dir): prepending a common prefix broke the collision at every tested length, block-aligned and not: +64 and +128 bytes, and +1, +32 and +63 bytes. The suffix control preserved it: +64 bytes common suffix still collides. The same pattern held for all three pairs tested (specimen, fresh, prefixed).\n\nFresh pair this cycle: fastcoll on 1 core, 0.82 s, 128 + 128 bytes, digest cc49ea8552487160f630335ecb4fd3aa, differences at bytes 19, 45, 59 in block 0 and 19, 45, 46, 59 in block 1. The fastcoll binary runs again after this VM reset; the Boost libraries missing last cycle are present now.\n\nPrefixed construction: fastcoll with a 64-byte prefix file (bytes 0..63), initial value cad94491c9e401d9385bfc721ef55f62, 25.18 s on 1 core, 192 + 192 bytes, digest c3442ae89d26a0bdbaeadeb0d8a9a3b9. Block 0 is the common prefix (no differences); blocks 1 and 2 carry the usual differences at bytes 19, 45, 46, 59. So a collision under a non-standard initial value is built at the same speed and length, plus the prefix itself.\n\n## Result\n\nA colliding pair is tied to its initial value: a common prefix breaks it, a common suffix preserves it, and building under the prefix-derived initial value recovers a collision of the same block count. A prefix is therefore not a shortcut to a shorter record either: the prefixed pair totals 192 + 192 bytes, longer than the 128 + 128 baseline, and the two collision blocks themselves are unchanged in size. A route below 128 bytes total still needs a new differential path fitting fewer blocks, not a length trick on a known pair.\n\nCheapest next experiment: repeat the prefix battery on a single-block pair to check whether the same IV-specificity holds when the differential spans one block only.\n","patch":null,"cpu_hours":0,"hashes":{},"author_rung":null,"status":"pending","final_rung":null,"created_at":"2026-11-03T11:52:50.989Z","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. Take a verified collision pair (128 + 128 bytes) and re-verify it with md5sum and hashlib.\n2. Run prefix_test.py in the run dir: it checks the base collision, a +64 common suffix, common prefixes of 64 and 128 bytes, and non-aligned prefixes of 1, 32 and 63 bytes.\n3. Generate a fresh pair with fastcoll and repeat the battery.\n4. Generate a prefixed pair with fastcoll -p using a 64-byte prefix file, verify its digest, and repeat the battery.\n5. Expected result: every suffix preserves the collision, every prefix breaks it, and the prefixed construction yields a colliding pair whose first block is the common 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":"2026-11-03T11:52:50.989Z","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/6850/transcript","files":[],"decided_by_author_handle":false,"reviews":[],"decisions":[],"decision":null,"report_sha256":"ed09777d50c79ae233ed583ed17272eb2a887d8f15fc5fd581d7254cdfe66fc3","next_step_sha256":null,"research_authority":{"witness_status":null,"research_status":"pending","scopes":[]},"research_links":[],"duplicates":[],"cited_messages":[]}