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Sequence Wallets support ERC-1271 Standard Contract Signature Verification to allow signing of transactions and messages.

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ERC-191 Ethereum Signed Data

Messages encoded with as ERC-191 Ethereum Signed Data are able to be created and signed as follows. 
import { Wallet } from '@0xsequence/wallet'

// Construct your Sequence Wallet (out of scope for this section)
const wallet: Wallet

const message = "Hello, World!"

const prefixedMessage = "\x19Ethereum Signed Message:\n" + len(message) + message
const signature = await wallet.signMessage(prefixedMessage)
The above will iterate through local, signing the message. If the threshold is reached, the signature is returned. Otherwise the library will iterate through the remote signers as well. The resulting signatures are joined and encoded as a hex string.

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ERC-712 Structured Data Signatures

ERC-712 Structured Data can also be signed in a similar fashion. 
import { Wallet } from '@0xsequence/wallet'
import { encodeTypedDataDigest } from '@0xsequence/utils'

// Construct your Sequence Wallet (out of scope for this section)
const wallet: Wallet

// Encode the typed data
const chainId = 1
const typedData = {
	types: {
		Person: [
			{ name: 'name', type: 'string' },
			{ name: 'wallet', type: 'address' },
			{ name: 'count', type: 'uint8' }
		]
	},
	primaryType: 'Person' as const,
	domain: {
		name: 'Ether Mail',
		version: '1',
		chainId: chainId,
		verifyingContract: '0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC'
	},
	message: {
		name: 'Bob',
		wallet: '0xbBbBBBBbbBBBbbbBbbBbbbbBBbBbbbbBbBbbBBbB',
		count: 4
	}
} 
const hashedData = encodeTypedDataDigest(typedData)

const signature = await wallet.signMessage(hashedData)
The above will iterate through local, signing the message. If the threshold is reached, the signature is returned. Otherwise the library will iterate through the remote signers as well. The resulting signatures are joined and encoded as a hex string.

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Verification

The signature can be verified by calling the isValidSignature method on the wallet. 
  /**
   * @notice Verifies whether the provided signature is valid with respect to the provided hash
   * @dev MUST return the correct magic value if the signature provided is valid for the provided hash
   *   > The bytes4 magic value to return when signature is valid is 0x1626ba7e : bytes4(keccak256("isValidSignature(bytes32,bytes)"))
   * @param _hash       keccak256 hash that was signed
   * @param _signatures Signature byte array associated with _data.
   *                    Encoded as abi.encode(Signature[], Configs)
   * @return magicValue Magic value 0x1626ba7e if the signature is valid and 0x0 otherwise
   */
  function isValidSignature(
    bytes32 _hash,
    bytes calldata _signatures
  ) public override virtual view returns (bytes4) {
    // Validate signatures
    (bool isValid,) = _signatureValidation(_hash, _signatures);
    if (isValid) {
      return SELECTOR_ERC1271_BYTES32_BYTES;
    }

    return bytes4(0);
  }
This will iterate through the combined signatures and validate that the resulting signature breaches the wallet’s threshold.
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