SHA-256 collision truncated to 48 bits

The locally verified collision is saved in collision.json. The inputs are literal UTF-8 strings with no trailing newline or zero byte.

Field	inputA	inputB
Input	identitymd-sha256-48:2529407	identitymd-sha256-48:14013952
Byte length	28	29
SHA-256	982915e7a9c29943c3a92478787f91a152cfdac962fe052297f900b3d91ea35d	982915e7a9c2a37130deb136c85bc2e61ce0a6a78b80ae9ff07c95f829fe9a38
First 48 bits, MSB	982915e7a9c2	982915e7a9c2

Method and attributable evidence

search.py enumerated ASCII strings identitymd-sha256-48:N, starting with N=0, and stored each SHA-256 six-byte prefix in an open-addressed table. It found the pair after 14,013,953 hash evaluations; the measured search-loop duration was 39.345 seconds, excluding table allocation.

verify.py reads the delivered JSON, checks its exact key set, algorithm and lambda, decodes the inputs, asserts their byte strings differ, and recomputes both complete digests using Python hashlib and the OpenSSL CLI. The two interfaces agreed on both complete digests. The CLI reported OpenSSL 3.0.13 (30 Jan 2024). Run from the repository root:

python3 artifacts/verify.py

Observed verification output:

inputA: bytes=28 sha256=982915e7a9c29943c3a92478787f91a152cfdac962fe052297f900b3d91ea35d
inputB: bytes=29 sha256=982915e7a9c2a37130deb136c85bc2e61ce0a6a78b80ae9ff07c95f829fe9a38
PASS: distinct inputs; shared first 48 bits = 982915e7a9c2

Conclusion and limits

The observed digest equality over the first six bytes establishes the requested 48-bit truncated collision (lambda=24). The full SHA-256 digests differ. These are local measurements, not an independent review: hashlib and the CLI may share an OpenSSL implementation. SIMD verification was not available in this environment, so its acceptance remains unobserved. No external research claims or estimated digests are used as evidence.