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Automatically merged updates to draft EIP(s) 3074 (#3346)
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Sam Wilson
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@ -15,7 +15,7 @@ Creates a new EVM instruction, analogous to `CALL` (`0xF1`), that sets `CALLER`
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## Abstract
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This EIP creates an EVM instruction (`NAMETBD`) which forwards a `CALL`, setting `CALLER` according to an ECDSA signature.
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This EIP creates an EVM instruction (`CALLFROM`) which forwards a `CALL`, setting `CALLER` according to an ECDSA signature.
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## Motivation
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@ -38,18 +38,18 @@ Additionally, the opcode shall:
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- Set the caller address based on an ECDSA signature.
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`NAMETBD` shall increase the call depth by one, in the same way as `CALL`. `NAMETBD` shall not increase the call depth by two (as it would if it first called into the sponsee account and then into the callee.)
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`CALLFROM` shall increase the call depth by one, in the same way as `CALL`. `CALLFROM` shall not increase the call depth by two (as it would if it first called into the sponsee account and then into the callee.)
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In a static context (such as the one created by `STATICCALL`), `NAMETBD` with a non-zero `value` shall exit the current execution frame immediately (in the same way `CALL` behaves with a non-zero value in a static context.)
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In a static context (such as the one created by `STATICCALL`), `CALLFROM` with a non-zero `value` shall exit the current execution frame immediately (in the same way `CALL` behaves with a non-zero value in a static context.)
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### Definitions
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- **`NAMETBD`** - the specific instruction encoded as `0xf9`, introduced by this EIP, which implements the `CALL` analogue.
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- **Transaction-like Package** - the signed arguments passed to `NAMETBD`.
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- **`CALLFROM`** - the specific instruction encoded as `0xf9`, introduced by this EIP, which implements the `CALL` analogue.
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- **Transaction-like Package (TLP)** - the signed arguments passed to `CALLFROM`.
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- **Sponsor** - the account which is responsible for paying gas fees and sending the transaction.
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- **Sponsee** - the account which signed the transaction-like package.
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- **Invoker** - the account or contract which contains `NAMETBD`.
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- **Callee** - the target of the call from `NAMETBD`.
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- **Invoker** - the account or contract which contains `CALLFROM`.
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- **Callee** - the target of the call from `CALLFROM`.
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### Conventions
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@ -66,7 +66,7 @@ In a static context (such as the one created by `STATICCALL`), `NAMETBD` with a
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#### Inputs
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`NAMETBD` shall require the following stack arguments:
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`CALLFROM` shall require the following stack arguments:
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| Stack | Value |
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| ---------- | ------------ |
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@ -75,7 +75,7 @@ In a static context (such as the one created by `STATICCALL`), `NAMETBD` with a
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| `top - 2` | `s` |
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| `top - 3` | `sponsee` |
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| `top - 4` | `type` |
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| `top - 5` | `nextra` |
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| `top - 5` | `extra` |
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| `top - 6` | `gas` |
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| `top - 7` | `callee` |
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| `top - 8` | `value` |
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@ -84,26 +84,25 @@ In a static context (such as the one created by `STATICCALL`), `NAMETBD` with a
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| `top - 11` | `retOffset` |
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| `top - 12` | `retLength` |
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The signature (`yParity`, `r`, `s`) arguments shall be computed from `secp256k1(keccak256(type || abi.encode(invoker, chainid, nextra, gas, callee, value, data)))`.
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The signature (`yParity`, `r`, `s`) arguments shall be computed from `secp256k1(keccak256(type || abi.encode(invoker, chainid, extra)))`.
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The arguments are defined to be:
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- `type: uint8` - [EIP-2718](./eip-2718.md) transaction type (currently always `SPONSORED_TYPE`);
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- `invoker: address` - the address of the invoker contract;
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- `chainid: uint256` - the chain id, as returned by the `CHAINID` (`0x46`) opcode;
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- `nextra: uint256` - extra data, which can be used in the invoker to implement replay protection;
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- `extra: uint256` - extra data, which can be used in the invoker to implement replay protection;
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- `callee: address` - address of the callee;
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- `gas: uint256` - exact gas limit which must be provided with the call into `NAMETBD`;
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- `gas: uint256` - exact gas limit which must be provided with the call into `CALLFROM`;
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- `value: uint256` - exact amount of Ether in wei to be received by the callee;
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- `data: bytes` - the calldata for the call into the callee;
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- `sponsee: address` - address of the sponsee;
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- `argsOffset: uint256`, `argsLength: uint256` - region of memory used as the calldata for the call into the callee, which should be equal to `data`;
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- `argsOffset: uint256`, `argsLength: uint256` - region of memory used as the calldata for the call into the callee;
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- `retOffset: uint256`, `retLength: uint256` - region of memory filled with the return data from the call into the callee; and
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- `yParity: uint8`, `r: bytes32`, `s: bytes32` - signature for the package.
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#### Outputs
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`NAMETBD` pushes the following two values onto the stack:
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`CALLFROM` pushes the following two values onto the stack:
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| Stack | Value |
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| ---------- | --------- |
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@ -117,9 +116,6 @@ The arguments are defined to be:
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- `type != SPONSORED_TYPE`
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- Invalid signature
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- The address recovered from `yParity`, `r`, and `s` does not match `sponsee`
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- Gas limit supplied with the call into `NAMETBD` is not equal to the signed `gas`
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- The transaction's remaining gas is less than the signed `gas`
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- The value sent with the call is not equal to the signed `value`
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`valid` shall be a one in all other cases.
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@ -140,40 +136,38 @@ The return data area accessed with `RETURNDATASIZE` (`0x3d`) and `RETURNDATACOPY
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### Gas Fees
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The gas fees for `NAMETBD` are calculated according to the following pseudo-code:
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The gas fees for `CALLFROM` are calculated according to the following pseudo-code:
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```python
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S_cd = len(data) # In 256-bit words, rounded up
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fees = 3200 + (6 * S_cd)
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fee = 3200
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if preconditions_good(...):
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return fees + cost_of_call(...)
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return fee + cost_of_call(...)
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else:
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return fees
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return fee
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```
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Where `len(data)` is the length of the region of memory defined by `argsOffset` and `argsLength`, rounded up to the nearest 256-bit word, and `cost_of_call(...)` is the cost of a `CALL` (`0xF1`) instruction with the same `gas`, `value`, `argsOffset`, `argsLength`, `retOffset`, and `retLength` arguments.
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Where `cost_of_call(...)` is the cost of a `CALL` (`0xF1`) instruction with the same `gas`, `value`, `argsOffset`, `argsLength`, `retOffset`, and `retLength` arguments.
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## Rationale
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### Omitting Arguments
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The signature arguments `value`, `chainid`, and `invoker` are not included in arguments to the instruction because they can be calculated by the instruction itself.
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The signature arguments `chainid` and `invoker` are not included in arguments to the instruction because they can be calculated by the instruction itself.
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### Two Return Values
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It is important to differentiate between a failure in `NAMETBD`'s preconditions versus a failure in the callee. Correctly implementing replay protection requires the invoker to change its state (i.e. burn the nonce) even if the callee fails; but doing so if, for example, the signature failed would be nonsensical. Several options exist for encoding these two failure cases: returning two stack elements, reserving a specific revert reason, or choosing different values in a single stack element.
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It is important to differentiate between a failure in `CALLFROM`'s preconditions versus a failure in the callee. Correctly implementing replay protection requires the invoker to change its state (i.e. burn the nonce) even if the callee fails; but doing so if, for example, the signature failed would be nonsensical. Several options exist for encoding these two failure cases: returning two stack elements, reserving a specific revert reason, or choosing different values in a single stack element.
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First, it's important to note that all three options are a deviation from the semantics of other `CALL` opcodes, but this deviation is unavoidable.
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Reserving a specific revert reason, for example `NAMETBD failed`, is a large departure from other instructions. An invoker would need to inspect the revert reason to determine whether the callee reverted, or the `NAMETBD` pre-conditions were invalidated, which implies reading and comparing memory values. Further, to remain sound if a callee were to revert with `NAMETBD failed`, `NAMETBD` would need to replace the return data with some other value.
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Reserving a specific revert reason, for example `CALLFROM failed`, is a large departure from other instructions. An invoker would need to inspect the revert reason to determine whether the callee reverted, or the `CALLFROM` pre-conditions were invalidated, which implies reading and comparing memory values. Further, to remain sound if a callee were to revert with `CALLFROM failed`, `CALLFROM` would need to replace the return data with some other value.
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Returning a single stack element with different values depending on the situation (ex. `0` on success, `1` when the pre-conditions are violated, and `2` when the callee reverts) introduces the opportunity for a subtle bug: it's trivially easy to misinterpret the return value (`CALL` returns non-zero on success), but it's much harder to ignore a whole new stack value.
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### Sponsee in Arguments
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Including `sponsee` in the arguments to `NAMETBD` is a gas optimization for invoker contracts implementing some replay protection based on the sponsee address. Without the `sponsee` argument, invokers would have to do their own `ecrecover` before calling into `NAMETBD` to verify/adjust any state for replay protection.
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Including `sponsee` in the arguments to `CALLFROM` is a gas optimization for invoker contracts implementing some replay protection based on the sponsee address. Without the `sponsee` argument, invokers would have to do their own `ecrecover` before calling into `CALLFROM` to verify/adjust any state for replay protection.
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### Reserving an [EIP-2718](./eip-2718.md) Transaction Type
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@ -185,13 +179,21 @@ Other approaches to sponsored transactions, which rely on introducing a new tran
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Besides better compatibility with AA, an instruction is a much less intrusive change than a new transaction type. This approach requires no changes in existing wallets, and little change in other tooling.
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`NAMETBD`'s single purpose is to set `CALLER`. It implements the minimal functionality to enable sender abstraction for sponsored transactions. This single mindedness makes `NAMETBD` significantly more composable with existing Ethereum features.
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`CALLFROM`'s single purpose is to set `CALLER`. It implements the minimal functionality to enable sender abstraction for sponsored transactions. This single mindedness makes `CALLFROM` significantly more composable with existing Ethereum features.
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More logic can be implemented around the `NAMETBD` instruction, giving more control to invokers and sponsors without sacrificing security or user experience for sponsees.
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More logic can be implemented around the `CALLFROM` instruction, giving more control to invokers and sponsors without sacrificing security or user experience for sponsees.
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### Lack of Replay Protection
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### What to Sign?
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Earlier approaches to this problem included mechanisms for replay protection. This proposal explicitly does not handle replay protection, but instead includes a signed-but-unused field (`nextra`) which is expected to be used by invoker contracts to implement replay protection. Delegating replay protection to the invoker sidesteps the issue of giving a precompile contract its own storage, while opening the door to more innovative replay protection methods in the future.
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Earlier approaches to this problem included mechanisms for replay protection, and also signed over value, gas, and other arguments to `CALLFROM`. Instead, this proposal explicitly delegates these responsibilities to the invoker contract.
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As originally written, this proposal specified a precompile with storage to track nonces. Since a precompile with storage is unprecedented, a later revision moved replay protection into the invoker contract, necessitating a certain level of user trust in the invoker, while also opening the door to more creative replay protection schemes in the future. Building on this idea of trusted invokers, the other signed fields in the transaction-like package were eliminated until only `invoker`, `chainid`, and `extra` remained.
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The motivation for including `invoker` is to bind a particular transaction-like package to a single invoker. If `invoker` was not part of the TLP, a malicious invoker could reuse the TLP to impersonate the EOA.
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While `chainid` is not strictly necessary, and could be enforced in the invoker contract, it's reasonable to assume every well-behaved invoker will check the chain id. Without `chainid`, a TLP would be valid on multiple chains.
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Finally, `extra` should be used by invoker contracts to implement replay protection and security around calldata, value, and other parameters. For example, an invoker may assume `extra` to be `keccak256(abi.encode(gas, value, nonce))`, guaranteeing that the sponsee intended to set those parameters to those specific values. Without `extra`, invokers would not be able to determine if other values (eg. `gas`, `value`, calldata, etc.) had been tampered with.
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## Backwards Compatibility
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@ -211,10 +213,13 @@ TODO
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- Checking `msg.sender == tx.origin` no longer prevents reentrancy. _Adding the pre-condition that `sponsor != sponsee` would restore this property._
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### Signature Verification & Reply Protection
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### Signature Verification, Reply Protection & `extra`
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- Potential impersonation attacks if there is a bug in the signature verification.
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- Replay protection can be poorly implemented (or even maliciously broken) in the invoker.
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- A naive invoker can _allow a malicious sponsor to take near complete control over a sponsee's EOA_, including but not limited to:
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- Causing a transaction-like package to fail if `CALLFROM` is provided insufficient `gas`; and
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- Replacing the sponsee's callee and/or calldata with other values.
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### Frontrunning
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