SHA-256 truncated to 48 bits: collision found

The requested collision is in collision.json, with exactly algo, lambda, inputA, and inputB. Lambda is 24; the comparison covers the first 48 most significant digest bits (the first six bytes).

Observed results

Input	Hex-encoded bytes	Full SHA-256 digest
A	0xe8f1380000000000	67171c0eb1922b1b1e7b76dd2213a661d3542f3c6b00e39279800abaaf50b502
B	0x23f68e0000000000	67171c0eb192a147eff93d18c3adf2a803bba554778ef76416669125a3a46e19

The two eight-byte inputs are distinct. Both digests begin with 67171c0eb192. The 0x prefix denotes hex decoding; it is not hashed as text.

Method and attributable evidence

A local C search hashed successive unsigned integers, starting at zero, encoded as eight bytes in little-endian order. It used OpenSSL 3.0.13 SHA256 and a hash table of six-byte digest prefixes. The matching integer values were 3731944 and 9369123, found after 9,369,124 candidate evaluations. The search also rehashed the earlier candidate to confirm the match.

The delivered verification script independently recomputes the submitted inputs with Python's standard-library hashlib, checks the exact JSON key set, algorithm, lambda, distinct decoded bytes, and equal six-byte prefixes. Run from the repository root:

python3 tools/verify_collision.py

Its successful output is preserved in verification.txt. A separate invocation of openssl dgst -sha256 on each decoded input also matched both full hashes. These are local computational observations, not external citations or independent review. Python and the OpenSSL command may share the same underlying hash library. The verifier requires only Python 3 and its standard library, with no network or third-party installation.

Conclusion and limits

The measured bytes satisfy the requested 48-bit prefix equality. The complete 256-bit digests differ; this is not a full SHA-256 collision. No probabilistic inference is needed to establish this particular equality. The external SIMD verifier was not available in this session, so its acceptance remains unobserved.