SHA-256 collision truncated to 48 bits

The requested collision was found and verified locally. The deliverable is ../collision.json, with exactly the four requested fields. Both inputs use 0x hexadecimal byte encoding, not the UTF-8 bytes of their displayed strings.

Computed evidence

Value	Input A	Input B
Input bytes (hex)	bc201a0000000000	1833c70100000000
Full SHA-256	2cf3eca701455ab0e389b24dfde1b77792816413a99905675280fdeaf9d8a699	2cf3eca70145a3bbedeb37083a53563ad127435c9da75d4043e7757969623573
First 48 bits (six leading digest bytes)	2cf3eca70145	2cf3eca70145

These are measured results from the local search and verifier, not assumed hash values. The distinct decoded byte strings and equal six-byte prefixes establish the requested truncated collision. The full digests differ.

Attribution and reproduction

The search implementation is ../tools/find_collision.cpp. It uses the installed OpenSSL 3.0.2 SHA256 function. It hashes 33,554,432 eight-byte little-endian integers in the first batch, sorts their 48-bit prefixes, then recovers and rehashes the matching inputs. It found this pair in that first batch.

The separate check is ../tools/verify_collision.py, which uses Python's hashlib.sha256 and checks the exact JSON field set, algorithm, lambda, distinct decoded inputs, and equality of the leading six digest bytes. Running it returned exit status 0 and:

Shared first 48 bits: 2cf3eca70145
PASS: distinct inputs, exact schema, matching 48-bit MSB prefixes

Recheck the delivered file offline:

python3 tools/verify_collision.py

Optional search reproduction (requires an installed C++ compiler and OpenSSL development library; these are not needed to consume the JSON):

mkdir -p test/scratch
g++ -O3 tools/find_collision.cpp -lcrypto -o test/scratch/find_collision
test/scratch/find_collision > test/scratch/reproduced.json

Limits and remaining uncertainty

This is a collision for the specified 48-bit MSB truncation, not for full SHA-256. All evidence above is attributable to this local execution. The Python check is a separate verification path, but no independent reviewer or SIMD verification was run in this environment. The external verifier's acceptance remains unanswered; local results carry no independent authority. There are no external research claims or citations required for these directly computed values.