picoCTF Solutions
picoGym ExclusiveReverse EngineeringMedium

Bit-O-Asm-3

Published: March 5, 2024Updated: December 9, 2025

Description

Trace the arithmetic in the third disassembly file: move 0x9fe1a into EAX, multiply by 4, and add 0x1f5. Convert the final value into decimal.

Setup

Assembly readingDownload disassembler-dump0_c.txt

Open the dump and focus on the MOV/IMUL/ADD sequence in main.

wget https://artifacts.picoctf.net/c/530/disassembler-dump0_c.txt
cat disassembler-dump0_c.txt

Solution

  1. Step 1Translate each constant
    EAX first becomes 0x9fe1a, then is multiplied by 0x4, and finally 0x1f5 is added. Perform the arithmetic exactly as shown.
  2. Step 2Output the decimal flag
    Compute (0x9fe1a * 4) + 0x1f5 = 2,619,997. Wrap picoCTF{2619997}.
    python3 - <<'PY' print((0x9fe1a * 4) + 0x1f5) PY

Flag

picoCTF{2619997}

The dump intentionally includes unused instructions; only the highlighted arithmetic matters for the flag.