SHA-256 first-48-bit collision

Found a collision for λ = 24, where the requested truncation is the first 48 bits (six bytes, or 12 hexadecimal digits) of SHA-256. The exact submission is collision.json.

Input (hexadecimal bytes)	Full SHA-256 digest
0x000000000017211c	4e84dca19fa699674e41dc0ff0f92046577a96fd3bbc22ae6a036986dc268301
0x00000000014060cc	4e84dca19fa67ad46fd0f73243c0081834a4767ce3fc91b0b4dade47ab574d2e

Both digest prefixes are 4e84dca19fa6. Inputs are decoded from hexadecimal into eight bytes; the literal characters 0x are not hashed. The inputs differ, and the full digests differ.

Attributable evidence and reproduction

The local search implementation used the system OpenSSL 3 SHA256 function and found this pair after 20,996,301 evaluations of consecutive big-endian counters starting at zero. Input A is counter 1,515,804; input B is counter 20,996,300.

The separate verification script recomputed both complete digests using Python 3 hashlib, checked distinct decoded inputs, checked the exact JSON keys and parameters, and compared the first six digest bytes through their 12 hex digits. Run from the repository root:

python3 artifacts/verify.py

This check passed locally. The table above records its actual output, not estimated hash values. The README also gives the search build and reproduction commands. No external factual sources were needed: the evidence is the provided input bytes and reproducible hash computation.

Limits

This result establishes only the requested 48-bit truncated collision. It does not establish a collision in full SHA-256. These are local checks, not an independent reviewer or SIMD attestation. No uncertainty remains in the locally computed prefix equality; independent acceptance remains for the caller to determine.