RIPEMD-160 collision, first 48 bits (λ = 24)

Found a collision between two distinct eight-byte inputs. The 0x values in collision.json represent decoded hexadecimal bytes, not the literal text of the hexadecimal strings.

Value	Input A	Input B
Input bytes	0x19bef10000000000	0x1022730100000000
Full RIPEMD-160 digest	902e5fc86be47b1e2a17de2aab65d4e765623a05	902e5fc86be4a99253faddc650510cb85e77233d
First 48 bits, MSB	902e5fc86be4	902e5fc86be4

Method and attributable evidence

search.c enumerated eight-byte little-endian counters, starting at 1, and computed RIPEMD-160 through the local OpenSSL 3.0.13 library. A hash table retained candidates; all potential matches were checked against all six prefix bytes. The search found counters 15,842,841 and 24,322,576 after enumerating 24,322,576 inputs, taking approximately 15 seconds locally. Candidate rechecks add digest evaluations beyond the number of enumerated inputs.

verify.py rereads the delivered JSON, checks its exact key set and algorithm/parameter values, decodes both inputs, confirms they differ, and recomputes both full digests. Its recorded output is verification.json. A separate invocation of the local openssl dgst -ripemd160 CLI on each decoded input returned the identical full digests listed above.

Reproduce from the repository root:

python3 artifacts/verify.py

To repeat the search on a machine with GCC and OpenSSL's libcrypto.so.3:

mkdir -p test/scratch
gcc -O3 -Wall -Wextra artifacts/search.c -o test/scratch/search -l:libcrypto.so.3
test/scratch/search
python3 artifacts/verify.py

Conclusion and limits

Observed fact: the distinct inputs have equal first six digest bytes. This satisfies the requested 48-bit truncation collision. Their full 160-bit digests differ. The conclusion follows directly from the locally recomputed bytes; no external factual sources or estimates are needed. Python and the CLI may share the OpenSSL implementation, so these checks are not an independent cryptographic implementation audit. SIMD verification was not run here and remains external to this submission.