**Challenge Description**:
A binary `challenge_final` that reads a string and outputs hashes. We are provided with `OUTPUT.txt` containing 54 hashes (32-hex chars each).

**Analysis**:
1. **Static Analysis**: The binary is statically linked and stripped. Strings analysis revealed `Achallenge_Afinal` symbols, suggesting it was compiled with the Opal Compiler (OCS) or a similar functional language runtime.
2. **Behavioral Analysis**: Running the binary with different inputs revealed that the output hashes change based on the input characters. Specifically, the $i$-th input character affects the $(i+2)$-th hash.
3. **Hash Verification**: Simple MD5/SHA verification of single characters failed. The hashes appear to be MD2 (hinted by the flag `MD2_1S...`), but we treated the binary as a black-box oracle.

**Solution**:
1. We observed that the binary can be used as an oracle. Since there is a direct correlation between the $i$-th input character and the $(i+2)$-th hash, we can brute-force the flag character-by-character.
2. We wrote a solver script `solve.py` that iterates through printable characters, constructs a candidate flag, runs the binary, and checks if the corresponding hash matches the target hash in `OUTPUT.txt`.
3. This efficiently recovered the flag one character at a time.

**Solver**: [solve.py](file:///home/mritunjya/ctf/2026/nullcon/rev/hashinator/solve.py)

**Flag**: `ENO{MD2_1S_S00_0ld_B3tter_Implement_S0m3Th1ng_ElsE!!}`