EIP-2242 Transaction postdata

[adlerjohn]

@guthlStarkware

As explained in the analysis, going through the EVM costs less than 0.3 gas per word.

This analysis, I’m presuming?

@guthlStarkware

For a calldata input of size N bytes, if this verification operations were done in the EVM, the gas cost would be 30 gas for the first invocation of keccak and 6 gas for each additional word (32 bytes), totaling 30+6 * N / 32 gas. Asymptotically (neglecting the first 30 gas) this gives a gas price of roughly 6 for every 32 bytes, or 0.2 gas per byte.

You’d have to account for the costs of Merkeizing the data (some schemes require this, rather than simple hashing), which would end up quite a bit higher. You’d also have to account for the cost of calldata itself, which is going to be 16 gas per byte. So the costs of performing this operation on-chain are actually quite high.

@guthlStarkware

I don’t see the point of adding an extra field

If you’re using fraud proofs, you can’t simply re-post a transaction and check the calldata, as the transaction’s calldata and the contract call’s calldata may be completely different:

https://twitter.com/nicksdjohnson/status/1155672897756774400

Additionally, the separate field is particularly useful for multi-threaded data availability, which is going to be the subject of a sister EIP.