SHA-256 collision in the first 48 bits

The requested collision is delivered in collision.json, with algo set to sha256 and lambda set to 24.

Inputs and attributable evidence

The 0x notation specifies raw hexadecimal bytes, not the UTF-8 bytes of the displayed strings. Both inputs are four bytes long and distinct.

Input	Full SHA-256 digest
0xcbf30800	42d3126a1bb92ad6a2138f822195f3ed5e0de0012a744fa33ab7c7d7c0e7c0f1
0x135d3400	42d3126a1bb90537137527a39d1b48b7824610ecc23716ab7787c31abf7290d0

Observed result: Both digests begin with the same six bytes, 42 d3 12 6a 1b b9. Six bytes are 48 bits, so these results establish the requested MSB-truncated collision. The full digests differ.

Provenance: On 2026-10-05, tools/find_collision.py searched consecutive nonzero unsigned 32-bit integers encoded as four little-endian bytes. A compact table retained six-byte SHA-256 prefixes and input indices. The search found this pair after 3,431,699 digest evaluations, taking approximately 10.38 seconds in this environment.

Local verification: tools/verify_collision.py checked the exact JSON key set, algorithm, lambda, distinct decoded bytes, and matching first six digest bytes. It recomputed each full digest with Python hashlib.sha256 and the OpenSSL command line (OpenSSL 3.0.13 30 Jan 2024). Both interfaces returned the full digests shown above. Run from the repository root:

python3 tools/verify_collision.py

Limits and unanswered questions

This is evidence for a collision in the first 48 bits only. It does not establish a collision in the complete 256-bit SHA-256 digest. The recorded checks are local checks, not an independent review; Python and OpenSSL may share a cryptographic backend. No SIMD verifier was available or run here, so acceptance by that verifier remains unobserved. No external factual sources are needed for this computed result: the inputs and reproducible digest calculations are the evidence.