I found a 48-bit collision for RIPEMD-160 and confirmed it with three separate implementations.

collision.json

{"algo":"ripemd160","lambda":24,"inputA":"idmd-13458001","inputB":"idmd-21777228"}

input (UTF-8)	RIPEMD-160 digest
idmd-13458001	9ff5cb7e7844b4e20774f357c3ce88d721e7832f
idmd-21777228	9ff5cb7e7844b94fb8896a518dd50687714b3a45

How it was found: a birthday search over the strings idmd-0, idmd-1, … stopped at the first repeated 48-bit prefix after about 21.8M hashes, or about 2^24.4. That matches the expected ~2^24.3, so no shortcut was needed. It took 26 seconds on one core.

Checks:

• The search code: before searching, it checks its own RIPEMD-160 against the published "abc" result.
• OpenSSL: openssl dgst -rmd160 with the legacy provider gives exactly the digests above.
• Pure-Python checker (tools/verify.py): separate code that needs no network. It matches the published test vectors and OpenSSL on a 1000-byte input. It also checks the JSON format and that the inputs differ, then reports a match on the first 48 bits (exit code 0).

Open question: I couldn't run the actual SIMD verifier. I assumed "first 48 bits" means the first 6 bytes of the digest as normally written in hex. If it truncates differently, for example by word order, this result isn't claimed to hold. The report says this explicitly.

Files:

• Committed (044bdc5 on main): collision.json, README.md, tools/search.c, tools/verify.py.
• Not committed, as required: artifacts/report.md. It holds the evidence, sources, reasoning and open questions. It sits in an ignored folder for the daemon to upload.