We have come to be very excited about this EIP over at statechannels.org as it allows for a novel contract architecture we might call synthetic-EOA-per-channel. We believe this is likely to be the most elegant and efficient architecture for state channels, offering a large reduction in blockchain state usage as well as an improved user experience.
The EIP authors introduced us to the idea of a “synthetic, externally-owned” account. It is somewhat like a contract account in that the associated private key is not known or used, but very different to a contract account in that it cannot have any code or storage. The address of the account is found by recovering the public key from a fixed message digest. For example, using an EIP-3074 digest:
digest = keccak256(MAGIC || padTo32Bytes(Invoker) || padTo32Bytes(0))
and a “synthetic signature”, constructed without the use of a private key*. Using the EIP-3074 digest hands complete control of the synthetic EOA to the Invoker, as explained in the EIP.
State channels may then be executed by participants sending funds directly to a synthetic EOA of their choice — one derived from the channelId, for example (which is roughly speaking the hash of the participants’ accounts). The Invoker can then release funds from the synthetic EOA conditional on all of the usual checks defined by the state channel protocol (e.g. the channelId itself, signatures on off-chain states, etc).
This avoids the need to i) have an additional “layer 2 accounting system” for state channels (i.e. no need to use contract storage to record which channel has how many tokens because the ethereum accounting system suffices), or ii) deploy a contract per channel using CREATE2 (which is expensive and will shortly become more so as SELFDESTRUCT refunds are removed) and also avoids the need to iii) approve and transferFrom tokens into the state channel in two separate transactions.
The bottom line from a state channels point of view is: improved state hygiene by avoiding writes to storage and/or code deposits and improved UX. Both imply increased gas efficiency. Projects like Connext are executing a high volume of state channels in production, making these improvements all the more significant.
*We would like a deterministic, reliable algorithm for this: it seems somewhat nontrivial and worthy of some more research.