S1C8: The Unverified

1. Problem

The contract is not verified on the block explorer (no source code). You need to understand the contract logic by analyzing the bytecode, then call the correct function.

2. Root Cause

The contract deliberately does not disclose its source code. Players need to possess EVM bytecode analysis skills.

3. Solution

Use cast code to obtain the deployed bytecode
Decode function signatures via 4-byte selectors
Analyze the function dispatch table and function logic
Construct the correct calldata and send the transaction

bash

# Obtain bytecode
cast code <CHALLENGE> --rpc-url $RPC
# Decode selector
cast 4byte <SELECTOR>
# Send raw calldata
cast send <CHALLENGE> <CALLDATA>

4. Pitfalls Encountered

Bytecode analysis complexity: Unverified contracts require manually tracing JUMPDEST, stack operations, and storage access.

5. Why the Pitfall Exists

EVM bytecode is a low-level representation without the semantic information of Solidity source code. It requires understanding EVM opcodes, ABI encoding, and the code patterns generated by the Solidity compiler.

6. How to Resolve

Use tools to assist with analysis:

cast selectors to list all function selectors
cast storage to read storage slots
Python scripts to parse dispatch tables and function bodies
Pay attention to revert strings (stored at the end of the bytecode, providing hints)

7. Key Takeaways

Point	Explanation
EVM bytecode analysis	Understanding dispatch tables, function selectors, and JUMPDEST structures
Function dispatch	Solidity uses a binary search + function selector dispatch pattern
Reverse engineering	Deriving Solidity source logic from bytecode
cast tools	`cast code`, `cast selectors`, `cast 4byte`, `cast storage`

S1C8: The Unverified #

1. Problem #

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3. Solution #

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