Puzzle 2 is very similar to Puzzle 1, with the only difference being that this time we need to understand the CALLVALUE opcode.

I recently discovered that the EVM Puzzle series is an excellent set of challenges to test our understanding of EVM opcodes. The puzzles can be found at this link: https://github.com/fvictorio/evm-puzzles. In this blog post, we will focus on solving the first puzzle.

The gist of this question is that the “Recovery” contract created a “SimpleToken” contract but lost the address of the SimpleToken contract. Now, the goal is to find the address of the SimpleToken contract and transfer the ETH inside it.

This question has a difficulty rating of 4 stars and is a very interesting one.

In ERC20, there is not only transfer function, but also transferfrom function.

In this question, even if the transfer function is overridden and there is a lockTokens modifier to prevent transfers, the transferFrom function in ERC20 is not overridden. We can utilize this function to perform transfers.

This question requires calculating an XOR value. To get the XOR value, we need to perform XOR operation again. The way the XOR value was originally calculated in the problem statement is the same logic that needs to be implemented in our smart contract code to get the XOR value.

This question is actually straightforward. It is similar to the previous one, but this time it requires brute force and understanding the value logic of unit32, uint64, uint160

This task is about how we store the varaibles in Solidity, how solidity allocates space for these variables.

This challenge requires us to change the value of top in the contract to true. By reading the logic of the goTo function, we are expected to implement the Building contract ourselves and ensure that the first call to isLastFloor returns false, and the second call returns true.

It is actually not difficult to implement this.