Keccak-256 collision in the first 48 bits
The requested collision is in ../collision.json. Both inputs are hexadecimal encodings of exactly eight bytes, not UTF-8 encodings of the displayed characters.
| Value | Result |
|---|
| inputA | 0x8375360100000000 |
| inputB | 0x7131040200000000 |
| Keccak-256(inputA) | 8851a59bbb9d6231d46ab9566296d3aed4afb5cd4212a1f68a094142b0366868 |
| Keccak-256(inputB) | 8851a59bbb9d27a12c8340ba34a0ac8820e6315e00542945f74d66f4ef53a9b1 |
| Common first 48 bits, MSB | 8851a59bbb9d |
Method and attributable evidence
The local birthday search in ../tools/search.c enumerated eight-byte little-endian counters starting at zero, computed Keccak-256 with 24 permutation rounds and Keccak padding, and stored six-byte digest prefixes in a hash table. It found the pair after 33,829,234 input evaluations. This count is the search program's observed output, excluding the two final digest computations.
The separate verifier in ../tools/verify.cjs uses the vendored js-sha3 version 0.9.3 source, authored by Chen, Yi-Cyuan, under the MIT license. The delivered ../tools/sha3.js has SHA-256:
6378cc474ad0a0db3e88c0c67b7bd4a154e1b318f44dbbd13927f6e220efaa38
Run offline from the repository root:
node tools/verify.cjs
The check passed locally. It validates the exact four JSON keys and requested algorithm/lambda, checks that the decoded bytes differ, and recomputes the full digests shown above using the separate implementation. It also checks the empty-string and abc Keccak-256 regression vectors. No installed package or network access is needed for verification.
Facts, inference, and limits
Observed facts: The delivered inputs differ as bytes. The C search and the separate JavaScript implementation produced the same full digests. Their first six bytes are identical. The verifier exited successfully.
Inference: These locally recomputed values satisfy the requested 48-bit truncation collision for lambda 24. The full 256-bit digests differ, so the result is a collision only under the requested truncation.
Uncertainty and unanswered questions: SIMD's external verification has not been run in this environment. These checks are reproducible local evidence, not independent review or a claim of external acceptance. No uncertainty remains about which bytes this submission intends to hash.