Signature Verification guide

docs/pages/guides/signature-verification.mdx

@@ -0,0 +1,93 @@
+# Signature Verification
+
+The are important details to verifying smart contract wallet signatures. The smart contract itself
+cannot produce a signature. Instead, the contract has a function
+```solidity
+function isValidSignature(bytes32 _hash, bytes memory _signature) returns (bytes4 magicValue);
+```
+which can be called to determine if signature should be considered valid (defined in [EIP-1271](https://eips.ethereum.org/EIPS/eip-1271)).
+
+In the case of Smart Wallet, a signature is considered valid if it was signed by a current signer (aka "owner") of the Smart Wallet.
+For example, a user can sign a message with their passkey, and when `isValidSignature` is called on their Smart Wallet,
+it would return that the signature is valid because their passkey is an owner.  
+
+There is also an additional complexity: users receive their Smart Wallet address immediately upon passkey registration,
+and are able to begin signing for their Smart Wallet,
+but their Smart Wallet is not deployed on a chain until the first transaction on that chain.
+
+[ERC-6492](https://eips.ethereum.org/EIPS/eip-6492) describes 
+> With the rising popularity of account abstraction, we often find that the best user experience 
+for contract wallets is to defer contract deployment until the first user transaction, 
+therefore not burdening the user with an additional deploy step before they can use their account. 
+However, at the same time, many dApps expect signatures, not only for interactions, but also just for logging in.
+
+So the challenge is, how do we verify signatures in a way that works for both deployed and undeployed Smart Wallets?
+ERC-6492 has a solution for this, which Smart Wallet has adopted. 
+We won't go unto all the details here, read the ERC linked above, if you're looking for that.
+Below we cover the minimum work needed to support on and off chain signature validation for Smart Wallet.
+
+## Offchain
+For purely offchain signature verification, simply ensure you are using 
+a ERC-6492-compliant signature verification library, and it all should *just work*. 
+We recommend [Viem's `verifyMessage`](https://viem.sh/docs/actions/public/verifyMessage#verifymessage).
+
+## Onchain
+For signatures that will be used onchain, such as with [Permit2](https://github.com/Uniswap/permit2) 
+or [Seaport](https://github.com/ProjectOpenSea/seaport) developers will need to inspect the signature offchain 
+and remove unneeded ERC-6492 data, if it is present. 
+
+:::code-group
+```ts twoslash [example.ts]
+import {parseERC6492Signature} from "./utils"
+
+const signatureForDeployedSmartWallet = "0x0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000400000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000c0000000000000000000000000000000000000000000000000000000000000012000000000000000000000000000000000000000000000000000000000000000170000000000000000000000000000000000000000000000000000000000000001517cb5e6438c7a32ba9bbc6766c6705c322c4f51bf28037af8f932e30e11c92e3b6b0080d3c2626ef4c6b0415ab036b47ca75ab9905753d7d3519fe09a56c98b0000000000000000000000000000000000000000000000000000000000000025f198086b2db17256731bc456673b96bcef23f51d1fbacdd7c4379ef65465572f0500000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000008a7b2274797065223a22776562617574686e2e676574222c226368616c6c656e6765223a22507a435038462d5252384b387557513241574d7650677032554f776362725774564d6e656856336f4a6530222c226f726967696e223a2268747470733a2f2f6b6579732e636f696e626173652e636f6d222c2263726f73734f726967696e223a66616c73657d00000000000000000000000000000000000000000000";
+const signatureForUndeployedSmartWallet = "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";
+
+parseERC6492Signature(signatureForDeployedSmartWallet)
+// @log: {
+// @log:   sigToValidate: 0x0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000400000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000c0000000000000000000000000000000000000000000000000000000000000012000000000000000000000000000000000000000000000000000000000000000170000000000000000000000000000000000000000000000000000000000000001517cb5e6438c7a32ba9bbc6766c6705c322c4f51bf28037af8f932e30e11c92e3b6b0080d3c2626ef4c6b0415ab036b47ca75ab9905753d7d3519fe09a56c98b0000000000000000000000000000000000000000000000000000000000000025f198086b2db17256731bc456673b96bcef23f51d1fbacdd7c4379ef65465572f0500000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000008a7b2274797065223a22776562617574686e2e676574222c226368616c6c656e6765223a22507a435038462d5252384b387557513241574d7650677032554f776362725774564d6e656856336f4a6530222c226f726967696e223a2268747470733a2f2f6b6579732e636f696e626173652e636f6d222c2263726f73734f726967696e223a66616c73657d00000000000000000000000000000000000000000000
+// @log: }
+
+parseERC6492Signature(signatureForUndeployedSmartWallet)
+// @log: {
+// @log:   sigToValidate: 0x0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000400000000000000000000000000000000000000000000000000000000000000260000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000c0000000000000000000000000000000000000000000000000000000000000012000000000000000000000000000000000000000000000000000000000000000170000000000000000000000000000000000000000000000000000000000000001946068e132450c0189690dc29c0eb20a504e6c5a02c42ebc647c83f4e4a2e61e786bea55ea4695b4b72ef88ea133647a07ef02f2e9c0bfd39457a7eb18b519bd0000000000000000000000000000000000000000000000000000000000000025f198086b2db17256731bc456673b96bcef23f51d1fbacdd7c4379ef65465572f050000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000f77b2274797065223a22776562617574686e2e676574222c226368616c6c656e6765223a2234446462577159355831784c6b77735133584e31754736754a526f5a3731354a4643397767643332413767222c226f726967696e223a2268747470733a2f2f6b6579732e636f696e626173652e636f6d222c2263726f73734f726967696e223a66616c73652c226f746865725f6b6579735f63616e5f62655f61646465645f68657265223a22646f206e6f7420636f6d7061726520636c69656e74446174614a534f4e20616761696e737420612074656d706c6174652e205365652068747470733a2f2f676f6f2e676c2f796162506578227d000000000000000000
+// @log:   factory: 0x0BA5ED0c6AA8c49038F819E587E2633c4A9F428a
+// @log:   factoryCalldata: 0x3ffba36f0000000000000000000000000000000000000000000000000000000000000040000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000004093a5e054721e22912d422ba5fca7ac395246e7f466b72c078bb987b71c5bf8ddf92c381340e22a301b823549d04765cd155a9b52206044121881395ab82d72c8
+// @log: }
+
+// use `ParseERC6492ReturnType.sigToValidate` for onchain validation.
+
+
+```
+```ts twoslash [utils.ts] filename="utils.ts"
+import {type Hex, type Address, decodeAbiParameters} from 'viem'
+
+export function isERC6492Signature(signature: Hex) : boolean {
+  const ERC6492_DETECTION_SUFFIX = "6492649264926492649264926492649264926492649264926492649264926492";
+  return signature.slice(signature.length - 64, signature.length) == ERC6492_DETECTION_SUFFIX;
+}
+
+export type ParseERC6492ReturnType = {
+  sigToValidate: Hex;
+  factory?: Address;
+  factoryCalldata?: Hex;
+};
+
+// NOTE: Works with non-ERC-6492 siganture
+// parseERC6492Signature(eoaSignature).sigToValidate == eoaSignature  
+// parseERC6492Signature(deployedSmartAccountSignature).sigToValidate == deployedSmartAccountSignature
+export function parseERC6492Signature(signature: Hex): ParseERC6492ReturnType {
+  if (!isERC6492Signature(signature)) return { sigToValidate: signature };
+
+  const [factory, factoryCalldata, sigToValidate] = decodeAbiParameters(
+    [
+      { type: "address" },
+      { type: "bytes" },
+      { type: "bytes" },
+    ],
+    signature,
+  );
+  return { sigToValidate, factory, factoryCalldata };
+}
+```
+:::

vocs.config.ts

@@ -57,6 +57,10 @@ export default defineConfig({
           text: 'Update an existing app',
           link: '/guides/update-existing-app'
         },
+        {
+          text: "Signature Verification",
+          link: '/guides/signature-verification'
+        },
         { 
           text: 'Batch transactions', 
           link: '/guides/batch-transactions',