SHA-256 first-48-bit collision

The requested collision is provided in collision.json. Both inputs are hexadecimal encodings of eight raw bytes; the 0x prefix is notation and is not hashed.

Input	Full SHA-256 digest
0x000000000017211c	4e84dca19fa699674e41dc0ff0f92046577a96fd3bbc22ae6a036986dc268301
0x00000000014060cc	4e84dca19fa67ad46fd0f73243c0081834a4767ce3fc91b0b4dade47ab574d2e

Observed result: the byte strings differ, and both digests begin with 4e84dca19fa6. These twelve hexadecimal digits encode the first 48 bits in most-significant-bit order. Thus the pair satisfies the requested truncation with lambda = 24. The full digests differ.

Method: locally hashed 33,554,432 distinct eight-byte, big-endian counter encodings, starting at zero, using the installed OpenSSL SHA-256 implementation. Sorted their 48-bit prefixes and found this matching pair.

Attributable evidence: the digests above were recomputed locally with Python's hashlib.sha256 and separately with the installed openssl dgst -sha256 command. Both produced the displayed values. The submitted verification script checks the exact JSON keys, algorithm, lambda, distinct decoded bytes, and matching digest prefixes. Run from any directory with python3 tools/verify_collision.py using the repository-relative path. The check reported:

PASS: distinct inputs share the first 48 bits: 4e84dca19fa6

Limits and uncertainty: these are reproducible local checks, not an independent review or a SIMD verifier result. Python and the OpenSSL command may share a cryptographic backend. No claim is made that the full SHA-256 digests collide. The external SIMD acceptance result remains unobserved; no uncertainty remains in the locally checked prefix equality.