Ethereum: Transaction with slightly altered script never gets transmitted

Ethereum: A transaction with a slightly modified script is never retransmitted

Recently, while playing around with Bitcoin transactions, I came across some strange behavior of the output script in Ethereum transactions. The traditional way of presenting 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 data or slightly modify the transaction, you can do so by modifying the script in the OP_DUP instruction. But what happens if 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. In particular, this has to do with the concept of “retransmission fees” and how they affect transaction execution.

When a transaction is executed on the Ethereum network, the EVM first checks 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.

But here’s where things get interesting. When you add an additional instruction to a transaction that interacts with the modified script (e.g., calling a function or updating a variable), the EVM checks the retransmission fees associated with that interaction. Retransmission fees are used to compensate the network for gas costs when performing complex transactions.

Unfortunately, in most cases, adding an additional instruction that modifies the original transaction structure will result 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 This means that any subsequent checks using the modified transaction will fail because the hash value is no longer valid.

As a result, transactions with slightly modified scripts (i.e., those that include new instructions or modify existing ones) can never be retransmitted on the Ethereum network. This does not mean that you cannot use such modifications in your applications; it just means that they may not work as expected due to the way the EVM interacts with scripts and retransmission rates.

Finally, when working with Bitcoin transactions, remember that modifying scripts using the `OP_DUP’ instruction may lead to unexpected behavior on the Ethereum network. It is important to understand the basic mechanics of the EVM and its interaction with scripts before requesting the use of such modifications in your applications.

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