RIPEMD-160 collision for the first 48 bits

The search found two distinct eight-byte inputs whose RIPEMD-160 digests share the first 48 bits. The requested machine-readable result is ../collision.json. Values prefixed by 0x represent decoded hexadecimal bytes, not the UTF-8 bytes of the displayed strings.

Field	Input A	Input B
Input bytes, hexadecimal	0000000000de27bb	000000000162a52d
Full RIPEMD-160 digest	18573a938b62f83d5fd18457e6667947098926a1	18573a938b62ac143bea6201e8a91fb007aa02ad
First six bytes (48 bits, MSB)	18573a938b62	18573a938b62

Method and attributable local evidence

The submitted search program enumerates positive integers encoded as eight-byte big-endian messages and stores their six-byte digest prefixes in an open-addressed table. The run found the match after 23,242,029 digest evaluations, in approximately 74.71 seconds. These are measurements from this local run, not performance guarantees.

On 2026-10-05, running python3 artifacts/verify.py from the repository root produced:

inputA: bytes=0000000000de27bb digest=18573a938b62f83d5fd18457e6667947098926a1 prefix48=18573a938b62
inputB: bytes=000000000162a52d digest=18573a938b62ac143bea6201e8a91fb007aa02ad prefix48=18573a938b62
PASS: distinct inputs; equal first 48 digest bits; both interfaces agree.

The verification program checks the exact JSON key set, algorithm and lambda, distinct decoded inputs, and equality of the first six digest bytes. It recomputes each full digest through Python hashlib and openssl dgst -ripemd160 -binary. The installed CLI reports OpenSSL 3.0.13 (30 Jan 2024). Verification requires no network or installed extras beyond those existing system tools.

Conclusion and limits

The locally observed digest equality establishes the requested 48-bit prefix collision under the stated hexadecimal decoding. The full digests differ; this is not a full 160-bit collision. Python and the CLI may share the same OpenSSL implementation, so agreement is not independent cryptographic implementation evidence. No SIMD verifier was available or run in this assignment; its acceptance remains unobserved. The local checks are reproducible evidence, not independent certification.