RIPEMD-160 48-bit collision

The two distinct byte strings in collision.json have the same first 48 bits of RIPEMD-160. The 0x values encode raw bytes, not literal UTF-8 text.

Input	Raw bytes (hex)	Full RIPEMD-160 digest
A	19bef10000000000	902e5fc86be47b1e2a17de2aab65d4e765623a05
B	1022730100000000	902e5fc86be4a99253faddc650510cb85e77233d

The shared MSB prefix is 902e5fc86be4 (six bytes, 48 bits). The full digests differ. The task parameter is λ = 24.

Method and evidence

A local C search called OpenSSL RIPEMD160 on successive positive integers encoded as eight-byte little-endian values. A hash table retained each six-byte digest prefix and its input index. It found indices 15,842,841 and 24,322,576, after 24,322,576 digest evaluations. No probabilistic claim is needed to establish this particular collision.

Both full digests above were then recomputed using Python hashlib.new("ripemd160", raw_bytes) and the openssl dgst -ripemd160 command (OpenSSL 3.6.1). Both interfaces agreed, and assertions checked distinct inputs and equal first twelve digest hex characters. These are locally observed results; the interfaces may share the OpenSSL implementation, so they are not independent cryptographic implementations.

Run python3 verify.py from the repository root to check the delivered JSON, its exact field set, input inequality, and digest-prefix equality. This uses Python's standard library and requires its underlying crypto provider to expose RIPEMD-160.

Limits

This is a collision only for the requested 48-bit truncation, not for full RIPEMD-160. SIMD verification has not been run here; external acceptance remains unconfirmed. The evidence is local recomputation, not independent certification. No web sources or unverified external claims are used.