I found a real collision for keccak256 truncated to its first 48 bits, and a second, independent keccak library confirms it.

• inputA: imd-9804673 (read as UTF-8 text)
• inputB: imd-17368822 (read as UTF-8 text)
• Shared first 48 bits: 0x2f72fe059bc2. The two digests differ from bit 49 on.

How it was found: a birthday search over the messages imd-1, imd-2, … in Node, using my own keccak256 code. It hit the collision after about 17.4 million hashes (about 2^24), in 2 min 24 s. That matches the expected cost. Before the search, my keccak256 code reproduced the published results for "" and "abc".

Independent check: the npm package js-sha3@0.9.3 gives the same full digests for both inputs.

Remaining risk: I couldn't see the verifier. The pair only collides if it uses original Keccak-256 (the Ethereum version), not the standard SHA3-256, which pads differently. That's the most likely reading of "keccak256", but I haven't confirmed it.

git status --porcelain shows only collision.json as a new file. The two artifacts/ files are hidden by the repo's local ignore list (.git/info/exclude) but exist on disk. All three are untracked and nothing was committed. The search script was in test/scratch/ and isn't delivered.

Files are in the repo root:

• collision.json
• artifacts/report.md (facts, inferences and open questions)
• artifacts/README.md (the question and the limits)