SHA-256 truncated to 48 bits: collision found

The answer is delivered in collision.json, with exactly the requested four fields. Inputs beginning with 0x denote decoded hexadecimal bytes, not the UTF-8 text of the hexadecimal representation. Both inputs are eight bytes long.

Observed evidence

Input	Bytes (hex)	Full SHA-256 digest
A	000000000017211c	4e84dca19fa699674e41dc0ff0f92046577a96fd3bbc22ae6a036986dc268301
B	00000000014060cc	4e84dca19fa67ad46fd0f73243c0081834a4767ce3fc91b0b4dade47ab574d2e

The distinct input bytes produce the same first six digest bytes: 4e84dca19fa6. Six bytes are 48 bits, corresponding to the requested lambda of 24. Their full digests differ.

Evidence is attributable to the local execution of tools/find_collision.py and tools/verify_collision.py during this assignment. The search hashed consecutive eight-byte big-endian counters beginning at zero, finding the match after 20,996,301 evaluations in approximately 56.75 seconds. The verifier independently recomputed both full digests through Python's hashlib.sha256 and the OpenSSL command line (OpenSSL 3.0.13). It checked the exact JSON field set, algorithm, lambda, distinct decoded inputs, agreement between the hash interfaces, and equality of the first six digest bytes. It exited successfully and printed:

PASS: common 48-bit MSB prefix 4e84dca19fa6

Inference and limits

The displayed byte equality establishes a collision for this 48-bit truncation under the specified hexadecimal decoding. This conclusion follows directly from the locally computed digests; it does not establish a collision for full SHA-256.

No independent reviewer or SIMD verifier was run here. Python and OpenSSL may share underlying cryptographic implementation code, so their agreement is not claimed as two independent cryptographic implementations. The downstream SIMD acceptance result remains unobserved. No external factual sources are needed for this computed result; the provided scripts and input bytes permit recomputation.