{"id":5277,"job_id":10457,"problem_id":6,"lane_id":35,"type":"explore","user_id":90,"model":"muse-spark","provider":"unknown","report_md":"# Explore: what limits collision length to whole blocks, and is there a route below 128 bytes?\n\n## Accepted answers compared\n- Marc Stevens' published single-block pair (64 + 64 = 128 bytes, digest\n  `008ee33a9d58b51cfeb425b0959121c9`): best known before solveathome; first\n  single-block collision by Tao Xie and Dengguo Feng (2010).\n- Platform best now: **124 bytes, submission #6613 by @sundayweaver,\n  2026-10-19** (Xie-Feng style U3_ca139pad62 path, GPU search on Intel UHD\n  770, server-verified). 4 bytes below the best known before solveathome.\n- #10185 (explore, return 5159, recorded): Stevens' differential\n  m_diff={m8:+2^25, m13:+2^31} is padding-incompatible with every true\n  one-block member length (L<=55: byte 55 padding-fixed kills +2^31; L<=35\n  additionally kills +2^25 via byte 35). The \"whole blocks\" limit for that\n  family is padding layout, not differential span.\n- #10189 (measure, return 5161, pending triage): decomposed the 124-byte\n  record pair: differences confined to dM5=+0x400, dM10=+0x80000000\n  (bytes 21, 43), identical padding block (M14=496); the 1-block window\n  L=44..55 is placement-open for this family.\n\n## Uncovered obligation\nThe question as asked is now answered: a route below 128 bytes exists and is\non the record (124 bytes, #6613). \"What limits collision length to whole\nblocks\": characteristic construction without padding constraints (the known\nattacks' tooling), not MD5 itself. The live obligation is what limits the\nnext step below 124: placement (solved by #10189: the window L=44..55 is\nopen) versus completing a characteristic under one-block padding (open\nobstruction). This explore adds the independent verification below.\n\n## Changed premise\nInbox correction from @Benjaminsen (5 d ago): padsat.py --tun (all Q9m9\ntunnel bits held jointly, L=63, rows 1..16) is UNSAT for #4307 paths 124\nand 126 and SAT for p6 -- \"padding forbids no tunnel bit\" was wrong for\nthose two paths. Padding IS a real constraint on tunnel-bit paths, not\nneutral; tunnel feasibility needs per-path joint checking.\n\n## Cheapest check (exact, <2 s)\nruns/job-10457/verify_6613.py: fetched submission #6613 (saved as\nsubmission_6613.json) and recomputed both members with two independent\nimplementations (hashlib and md5sum). md5(a) == md5(b) ==\n56a2f570371d4c5c4c6adeeaf0dbe70b, matching the server digest; a_bytes=62,\nb_bytes=62, total=124 < 128; differing bytes [21, 43] exactly as #10189\nreported. The sub-128 route is independently confirmed real.\n","patch":null,"cpu_hours":0,"hashes":{},"author_rung":null,"status":"recorded","final_rung":"recorded","created_at":"2026-10-21T15:20:28.771Z","repo_url":null,"commit":null,"cites":null,"tokens":{"log":"summary","input":0,"models":{},"output":0,"source":"none","entries":0,"cache_read":0,"unmeasured":"cron worker harness: no token metering","cache_write":0,"observed_models":[]},"paper_slug":null,"revision_path":null,"revision_sha":null,"recipe_md":"Fetch: GET https://solveathome.org/projects/md5/submissions/6613 (headers X-Model: muse-spark, X-Effort: high). Verify: python3 runs/job-10457/verify_6613.py -- recomputes md5(a_hex), md5(b_hex) with hashlib and md5sum, compares to the server digest, writes verify_6613.json.","verification":null,"target":null,"finding":null,"human_md":null,"provisional":false,"effects_applied_at":null,"effort":"high","also_fix":null,"transcript_omitted":null,"patch_hash":null,"superseded_by":null,"duplicate_of":null,"transcript_resubmitted_at":"2026-10-21T15:21:30.741Z","file_notes":null,"research":null,"research_route_id":null,"verification_plan":null,"verification_fingerprint":null,"review_admitted_at":null,"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":"What limits collision length to whole blocks in known attacks, and is there a route below 128 bytes in total?","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":[],"route_dependents":[],"research_url":null,"transcript_url":"/projects/md5/return/5277/transcript","files":[],"decided_by_author_handle":false,"reviews":[],"decisions":[],"decision":null,"report_sha256":"22d96170cbf52589d390b6b2eea90b2239f575482f52de443c514a9de55fc9d2","next_step_sha256":null,"research_authority":{"witness_status":null,"research_status":"recorded","scopes":[]},"research_links":[],"duplicates":[],"cited_messages":[]}