EVM Puzzle 1 - Warm Up!

Introduction

EVM puzzles provide a hands-on way to grasp the nuances of how the Ethereum Virtual Machine operates. This series will explore these puzzles, offering in-depth analysis and solutions.

Puzzle #1

00      34      CALLVALUE
01      56      JUMP
02      FD      REVERT
03      FD      REVERT
04      FD      REVERT
05      FD      REVERT
06      FD      REVERT
07      FD      REVERT
08      5B      JUMPDEST
09      00      STOP
        

The goal is to craft a transaction that executes this contract successfully (without encountering a revert).

Understanding EVM Puzzles

Before diving in, let's outline a general approach to solving EVM puzzles:

1. Disassembly: Convert the raw bytecode into a more readable opcode format using an EVM disassembler. See above output of a disassembler. For larger contracts this can be a huge list.
2. Analysis: Meticulously examine the opcodes. Understand their functions and how they interact. Pay close attention to jumps, conditional logic, and data manipulations.
3. Experimentation: Test hypotheses using an EVM debugger or a local Ethereum test environment. Send transactions with varying inputs and observe the results.

Key Concepts

Reminder of relevant EVM concepts:

• Opcodes: The building blocks of EVM execution.
• Stack: Temporary data structure for operations.
• Memory: Short-term storage during execution.
• Storage: Long-term data associated with the contract.

Solution

Let's analyze the bytecode: https://www.evm.codes/

• 34 CALLVALUE: Pushes the amount of Ether sent with the transaction onto the stack.
• 56 JUMP: Unconditionally jumps to the location marked by JUMPDEST (opcode 5B).
• FD REVERT: Multiple revert instructions, halting execution and rolling back state changes.
• 5B JUMPDEST: Marks a jump destination from top of the stack.
• 00 STOP: Terminates contract execution.

The Catch: For successful execution, you must avoid the REVERT opcodes. The JUMP immediately sends execution to the JUMPDEST. The only way to reach the STOP opcode (and succeed) is to ensure the CALLVALUE is 8.

The Stack:

[8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]        

Successful Transaction: You must send the jump destination to jumpdest so enter the location 8 solves the puzzle.

Stay tuned for Puzzle #2 in the EVM Puzzle, where the challenges intensify!

Let me know if you'd like to add extra complexity or nuances to future puzzles!

More Tools

I found tons of tools for working with the EVM. I am just going to drop them here and figure out overtime which ones are most useful

https://github.com/fvictorio/evm-puzzles

https://www.ethervm.io/