Merge pull request #1702 from sorpaas/sp-account-versioining

EIP-1702: Generalized Account Versioning Scheme

EIPS/eip-1702.md

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+---
+eip: 1702
+title: Generalized Account Versioning Scheme
+author: Wei Tang (@sorpaas)
+discussions-to: https://github.com/sorpaas/EIPs/issues/2
+status: Draft
+type: Standards Track
+category: Core
+created: 2017-12-30
+---
+
+## Abstract
+
+This defines a method of hard forking while maintaining the exact
+functionality of existing account by allowing multiple versions of the
+virtual machines to execute in the same block. This is also useful to
+define future account state structures when we introduce the on-chain
+WebAssembly virtual machine.
+
+## Motivation
+
+By allowing account versioning, we can execute different virtual
+machine for contracts created at different times. This allows breaking
+features to be implemented while making sure existing contracts work
+as expected.
+
+Note that this specification might not apply to all hard forks. We
+have emergency hard forks in the past due to network attacks. Whether
+they should maintain existing account compatibility should be
+evaluated in individual basis. If the attack can only be executed once
+against some particular contracts, then the scheme defined here might
+still be applicable. Otherwise, having a plain emergency hard fork
+might still be a good idea.
+
+## Specification
+
+### Account State
+
+Re-define account state stored in the world state trie to have 5
+items: `nonce`, `balance`, `storageRoot`, `codeHash`, and
+`version`. The newly added field `version` is a 256-bit integer. When
+`version` is zero, the account is RLP-encoded with the first 4
+items. When `version` is not zero, the account is RLP-encoded with 5
+items.
+
+### Contract Deployment
+
+In Ethereum, a contract has a deployment method, either by a contract
+creation transaction, or by another contract. If we regard this
+deployment method a contract's *parent*, then we find them forming a
+family of contracts, with the *root* being a contract creation
+transaction.
+
+We let a family of contracts to always have the same `version`. That
+is, `CREATE` and `CREATE2` will always deploy contract that has the
+same `version` as the calling `address`.
+
+### Validation
+
+A new phrase, *validation* is added to contract deployment (by
+`CREATE` / `CREATE2` opcodes, or by contract creation
+transaction). When `version` is `0`, the phrase does nothing and
+always succeeds. Future VM versions can define additional validation
+that has to be passed.
+
+If the validation phrase fails, deployment does not proceed and return
+out-of-gas.
+
+### Contract Execution
+
+VM version used in contract execution is determined via calling
+`address` (`I_a` in yellow paper). Precompiled contract does not have
+version.
+
+### Contract Creation Transaction
+
+Define `LATEST_VERSION` in a hard fork to be the latest supported VM
+version. A contract creation transaction is always executed in
+`LATEST_VERSION`. Before a contract creation transaction is executed,
+run *validation* on the contract creation code. If it does not pass,
+return out-of-gas.
+
+#### Alternative Design for Contract Creation Transaction
+
+This provides an alternative design that allows contract to be created
+in multiple versions.
+
+Add an additional field `version` (256-bit integer) in contract
+creation transaction. So it becomes `nonce`, `gasprice`, `startgas`,
+`to`, `value`, `data`, `v`, `r`, `s`, `version`. When signing or
+recovering, sign ten items, with `v`, `r`, `s` as defined by EIP-155.
+
+The transaction would be executed in `version` supplied. If `version`
+is not supported or *validation* does not pass, return out-of-gas.
+
+## Discussions
+
+### Performance
+
+Currently nearly all full node implementations uses config parameters
+to decide which virtual machine version to use. Switching vitual
+machine version is simply an operation that changes a pointer using a
+different set of config parameters. As a result, this scheme has
+nearly zero impact to performance.
+
+### Smart Contract Boundary and Formal Verification
+
+Many current efforts are on-going for getting smart contracts formally
+verified. However, for any hard fork that introduces new opcodes or
+change behaviors of existing opcodes would break the verification of
+an existing contract has previously be formally verified. Using the
+scheme described here, we define the boundary of how a smart contract
+interacts with the blockchain and it might help the formal
+verification efforts:
+
+* A smart contract has only immutable access to information of
+  blockchain account balances and codes.
+* A smart contract has only immutable access of block information.
+* A smart contract or a contract creation transaction can modify only
+  its own storage and codes.
+* A smart contract can only interact with the blockchain in a mutable
+  way using `CALL` or `CREATE`.
+
+### WebAssembly
+
+This scheme can also be helpful when we deploy on-chain WebAssembly
+virtual machine. In that case, WASM contracts and EVM contracts can
+co-exist and the execution boundary and interaction model are clearly
+defined as above.