I'll start by checking the environment — available tools, CPU, memory, and repo layout.Empty repo, 2 cores, ~3.8GB free RAM, gcc available. Now let me check whether RIPEMD-160 is available via OpenSSL/Python for independent verification.hashlib supports ripemd160 — that gives me an independent oracle to check my C implementation against. Let me set up the workspace.OpenSSL CLI and hashlib agree — I have a solid oracle (ripemd160("abc") = 8eb208f7e05d987a9b044a8e98c6b087f15a0bfc).

Plan: write an independent RIPEMD-160 in C, validate it against published vectors + OpenSSL, then run a birthday search (~2^24 evals expected) over 8-byte counter inputs, storing truncated digests in an open-addressing table.Now the self-test, a CLI hasher, and the collision search program.Compile and run the self-test.All 9 official vectors pass. Now a randomized cross-check against hashlib on arbitrary binary inputs to rule out subtle padding/endianness bugs.Implementation verified — 300/300 random inputs match OpenSSL. Now run the birthday search (expected ~2^24.3 ≈ 17M evaluations).Collision found after ~23.2M evaluations in 7.6s. Now verify it independently with Python hashlib and the OpenSSL CLI.Verified by a second implementation. Now add the durable pieces: a Makefile, a verifier script, README, and the report.Run a clean end-to-end check via the Makefile, then commit the source.Bug in my verifier: λ=24 means 48 bits total → 12 hex chars, not 2*λ hex chars. Fixing.All checks pass. Now commit the source files (outputs stay untracked per the delivery rules).No git identity configured — I'll pass it per-command without modifying config.Done. Verified collision found and delivered.

Result (collision.json):

{"algo":"ripemd160","lambda":24,"inputA":"0x000000000162a52d","inputB":"0x0000000000de27bb"}

• ripemd160(inputA) = 18573a938b62ac143bea6201e8a91fb007aa02ad
• ripemd160(inputB) = 18573a938b62f83d5fd18457e6667947098926a1
• Shared 48-bit MSB prefix: 18573a938b62 — inputs distinct, digests differ after byte 6.

How it was produced. Classical birthday search over 8-byte big-endian counter inputs (distinct by construction), storing the top 48 digest bits in a 2^26-slot open-addressed table. Found after 23,242,030 evaluations (~7.6 s) — in line with the ~2^24.3 birthday bound.

Verification. The search uses an independent C implementation of RIPEMD-160 (src/ripemd160.c) validated against all 9 official test vectors plus 300 random inputs cross-checked against OpenSSL — zero mismatches. The collision itself was re-verified with a different implementation (hashlib/OpenSSL) via tools/verify_collision.py: make check passes end-to-end. bin/collide 26 is deterministic and regenerates the same pair.

Deliverables.

• collision.json — untracked output, exact required schema
• artifacts/report.md — report with method, evidence, and facts/inference/uncertainty separated
• Committed source: src/ (hash, self-test, search, CLI), tools/verify_collision.py, Makefile, README.md