The requested 48-bit Keccak-256 prefix collision was found and verified locally. The exact submission is collision.json, with exactly the four requested keys and lambda = 24. Inputs use hexadecimal byte encoding; the literal characters 0x are not hashed.

Field	Computed value
inputA	0x21777c0300000000
inputB	0x7c07d30300000000
Keccak-256(inputA)	de79868ee98d13a795141c8199c2738dd9598f9551ac24b1f8af7905053a3db5
Keccak-256(inputB)	de79868ee98dedfc4ce0c5e025c120952ba58728aa18a497f5ba1086098e40f3
Shared first 48 bits (six digest bytes, MSB prefix)	de79868ee98d

These are observed computations, not estimated digests. The two eight-byte inputs are distinct, and the full digests differ after their matching prefix.

The birthday search hashed sequential eight-byte little-endian counters and stored 48-bit prefixes in an open-addressed table. Counters 0 through 33,554,431 produced no match within that range. The second run started at 33,554,432 and found counters 58,488,609 and 64,161,660 after 30,607,229 evaluations in that run: 64,161,661 total search evaluations across both runs. The table was reset between runs, so matches between different ranges were not tested. The first run used loops; the second used equivalent unrolled round operations to reduce execution time.

Verification executed successfully:

• python3 tools/verify.py: exact schema and parameters, distinct decoded inputs, matching first six bytes, and agreement of both full digests with the bundled XKCP reference implementation. Both implementations also passed known-answer checks for empty input and abc.
• Twelve differential Python checks at message lengths 0, 1, 7, 8, 32, 134, 135, 136, 137, 271, 272, and 4096 bytes, including rate-boundary cases: passed.
• 105 comparisons of the unrolled C search's prefix computation with the Python verifier, including range endpoints and 100 consecutive counters: passed.

The final verification output is preserved in verification.txt. The search progress is preserved in search-first.txt and search-success.txt. Reproduce the successful range with python3 tools/run_search.py 33554432. Verify the result without searching with python3 tools/verify.py. All added dependencies are bundled as ordinary files; verification requires only Python 3 and no network. Search reproduction uses the bundled Linux amd64 TCC compiler and the host Python/glibc runtime.

The permutation and padding conventions follow the Keccak team's specification summary. The verifier uses rate 1088, capacity 512, 32 output bytes, and suffix 0x01 for Keccak-256. SHA3-256 uses a different suffix. The separately authored cross-check is Gilles Van Assche's XKCP implementation, pinned to commit 4affab454735d54e78156880b3b44e38dcbf765c, included unmodified with its CC0 waiver. Dependency provenance and checksums are in PROVENANCE.md.

The evidence establishes a locally recomputed 48-bit prefix collision, not a full 256-bit collision. There is no probabilistic inference needed to compare the displayed prefixes. These checks were performed by this contributor and carry no independent reviewer authority. SIMD's separate recomputation has not been run here; its acceptance remains unobserved. No other unanswered question is needed to reproduce the local result.