Stage 1: Bytecode Analysis
📜 Bytecode Program
0x0000: 01: PUSH 0x41 ('A')
0x0001: 01: PUSH 0x42 ('B')
0x0002: 03: ADD
0x0003: 12: PRINT
0x0004: 14: HALT
Bytecode Decoder Tool
Challenge Information
🎯 Objective: Analyze custom VM bytecode to extract the hidden flag.
🏆 Target Flag: CTF{VM_BYTECODE_REV_2024}
⏱️ Time Estimate: 20-30 minutes
🔧 Skills Required: Assembly understanding, hex analysis, pattern recognition
VM Instruction Set
| Opcode | Instruction | Description |
|---|---|---|
| 0x01 | PUSH | Push value onto stack |
| 0x02 | POP | Pop value from stack |
| 0x03 | ADD | Add top two stack values |
| 0x04 | SUB | Subtract top two stack values |
| 0x05 | MUL | Multiply top two stack values |
| 0x06 | DIV | Divide top two stack values |
| 0x07 | XOR | XOR top two stack values |
| 0x08 | AND | AND top two stack values |
| 0x09 | OR | OR top two stack values |
| 0x0A | CMP | Compare top two stack values |
| 0x0B | JMP | Unconditional jump |
| 0x0C | JE | Jump if equal |
| 0x0D | JNE | Jump if not equal |
| 0x0E | LOAD | Load from memory |
| 0x0F | STORE | Store to memory |
| 0x10 | CALL | Call subroutine |
| 0x11 | RET | Return from subroutine |
| 0x12 | Print top of stack | |
| 0x13 | READ | Read input |
| 0x14 | HALT | Stop execution |
Learning Objectives
- Understand custom virtual machine architectures
- Learn bytecode analysis and disassembly techniques
- Practice reverse engineering without source code
- Recognize cryptographic patterns in bytecode
- Develop systematic analysis methodologies