Ethereum: A transaction with a slightly modified script is never committed
While recently playing around with Bitcoin transactions, I came across some strange behavior with the result script for Ethereum transactions. The traditional way to represent transactions on the Ethereum network uses the following format:
OP_DUP OP_HASH160 (hash) OP_EQUALVERIFY OP_CHECKSIG
This structure allows for hash-based verification, which is necessary to ensure the integrity and authenticity of digital signatures.
However, there is an interesting twist to this setup. When you want to include additional information or modify the transaction slightly, you can do so by modifying the script in the OP_DUP instruction. But what happens when you add a new instruction that interacts with this modified transaction?
The answer lies in the Ethereum Virtual Machine (EVM) and its interaction with scripts. Specifically, it has something to do with the concept of “commission fees” and how they affect the execution of transactions.
When a transaction is executed on the Ethereum network, the EVM first validates the hash of the input data. If the hash matches the expected value, the transaction proceeds. However, if the hash does not match, the transaction fails.
Now, things get interesting. When you add an additional instruction to your transaction that interacts with the modified script (e.g., calling a function or updating a variable), the EVM checks for any transaction fees associated with that interaction. Transaction fees are used to offset the network’s gas costs for executing complex transactions.
Unfortunately, in most cases, adding an additional instruction that modifies the original transaction structure results in the OP_DUP instruction being executed multiple times, each time checking a different hash value. This means that any subsequent checks using the modified transaction will fail because the hash values are no longer valid.
As a result, transactions with slightly changed scripts (i.e., those that contain new instructions or modify existing ones) may never be transmitted on the Ethereum network. This does not mean that you cannot use such modifications in your applications. It is just that they may not work as expected due to the way the EVM interacts with scripts and transaction fees.
In summary, when playing with Bitcoin transactions, keep in mind that modifying scripts using the OP_DUP instruction can lead to unexpected behavior on the Ethereum network. It is important to understand the mechanics behind the EVM and its interaction with scripts before attempting to use such modifications in your applications.