EVM Puzzles Challenge 1

18 Apr 2022 • EVM Puzzles Write-ups

Setting up the environment:

  1. First things first, clone the EVM puzzles repo. This contains all of the challenges we’ll be going through to improve our understanding of EVM byetecode.
  2. Get familiar with the tools we’ll be using by reading through the hardhat docs and playing around with evm.codes
  3. Optional: Read and walkthrough 1st portion of noxx’s EVM series

Challenge:

Our first challenge is located in /puzzles/puzzle_1.json. Challenge 1 contains the following:

{
  "code": "3456FDFDFDFDFDFD5B00",
  "askForValue": true,
  "askForData": false
}
Hint 1: 
The "code" section contains EVM bytecode. 
Try converting that to opcodes.

(one way is to drop the bytecode into evm.codes)

Hint 2: 
The corresponding EVM opcodes are:

CALLVALUE	
JUMP	
REVERT	
REVERT	
REVERT	
REVERT	
REVERT	
REVERT	
JUMPDEST	
STOP

The goal of this challenge is to not cause a revert.
Hint 3: 
CALLVALUE takes the value of the current call in wei
and places it on top of the stack. 
JUMP takes the value on the top of the stack and moves
the program counter to the offset of that value.


How can we JUMP over the 6 REVERT 
opcodes and land on the JUMPDEST?
Hint 4: 
Each of the opcodes are 1 byte in size
Hint 5: 
CALLVALUE //Offset 0	
JUMP	  //Offset 1
REVERT    //Offset 2	
REVERT    //Offset 3	
REVERT    //Offset 4	
REVERT    //Offset 5	
REVERT    //Offset 6	
REVERT    //Offset 7	
JUMPDEST  //Offset 8
STOP
Solution: 
To solve this level, we just need to pass in a value of 8 
wei, so that CALLVALUE places 8 on the top of the stack 
and JUMP performs a valid jump over the REVERT calls to JUMPDEST.

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