Signing Transactions Offline

[emkman]

Support for signing transactions offline for sending to a locked node or potentially Infura would be extremely helpful. Similar functionality can be found in the ethereumjs-tx for javascript. Much of this functionality exists across the parity codebase and needs to be pieced together. In discussing this with @tomusdrw, the general steps required would be:

1. Encode contract call (this can be done by ethabi)
2. Create and fill a transaction request (nonce, gas, gasprice, etc) - I believe there is an RPC method to do that in Parity
3. Encode the transaction into RLP
4. Calculate hash and sign (this could be done by ethkey library)
5. Broadcast signed transaction

[synlestidae]

EDITED

Been interested in having this functionality since I came across the web3 crate.

We could implement web3::api::Eth::sign_transaction. Or maybe create a RawTransaction struct with a sign method. When I first made this issue I thought we just need to utilise web3.eth.accounts.signTransaction. Turns out offline signing is not even supported by the web3.js project.

[synlestidae]

The output of sign_transaction would be the RLP-encoded transaction that can be fed into send_raw_transaction.

[tomusdrw]

Most likely integrate with https://github.com/tomusdrw/ethsign

[steveswing]

Most likely integrate with https://github.com/tomusdrw/ethsign

We used ethsign with web3 indirectly -- in https://github.com/SubstratumNetwork/SubstratumNode -- but had to copy RawTransaction to work around type conflicts between web3::types, ethereum-types, and primitive-types.

[tomusdrw]

@steveswing cool! Yeah, there is no proper transaction type around (except for parity repo, but you really don't want to reference that in your code). I also wanted to avoid it in ethsign (initially), but would be happpy to include it at some point, along with different signature payloads that Ethereum is using (signData, signTransaction, etc)).