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Documentation Index

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Overview

DynamicEvmWalletClient::signMessage signs raw bytes using EIP-191 (personal_sign) and returns a 0x-prefixed r || s || v signature (65 bytes / 130 hex chars). Message signing is commonly used for authentication, nonce verification, and data integrity checks. The SDK also exposes an off-chain verifier — DynamicEvmWalletClient.verifyMessageSignature(...) — for recovering the signer locally without any MPC or network I/O.

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Prerequisites

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Basic Message Signing

The Java SDK is stateless — every sign call requires walletProperties and externalServerKeyShares. Load both from where you persisted them at wallet creation time. 
import java.util.List;
import xyz.dynamic.waas.ServerKeyShare;
import xyz.dynamic.waas.core.types.WalletProperties;
import xyz.dynamic.waas.evm.DynamicEvmWalletClient;
import xyz.dynamic.waas.opts.SignMessageOpts;

// Load the metadata + shares you persisted at creation time.
WalletProperties walletProperties = WalletProperties.fromJson(
    redis.get("wallet:" + accountAddress)
);
List<ServerKeyShare> externalServerKeyShares = ServerKeyShare.fromJsonList(
    vault.read("wallet:" + accountAddress + "/shares")
);

String signature = client.signMessage(SignMessageOpts.builder()
    .message("Hello, World!".getBytes(java.nio.charset.StandardCharsets.UTF_8))
    .walletProperties(walletProperties)
    .externalServerKeyShares(externalServerKeyShares)
    .build()
).join();

System.out.println("Signature: " + signature);
signature is a 0x-prefixed hex string — pass it directly to any EIP-191 verifier (web3j, ethers, viem, etc).

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Verifying the signer locally

Because the signature is standard EIP-191, you can recover the signer with the SDK’s static helper — no MPC ceremony, no network I/O: 
boolean ok = DynamicEvmWalletClient.verifyMessageSignature(
    walletProperties.accountAddress(),
    "Hello, World!".getBytes(java.nio.charset.StandardCharsets.UTF_8),
    signature
);
assert ok : "signature does not match accountAddress";
verifyMessageSignature hashes the message via EIP-191, recovers the signer address from (r || s || v), and compares it case-insensitively to accountAddress. Returns false on any structural failure (bad length, bad recovery, mismatch).

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Common Use Cases

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Authentication

String nonce   = String.valueOf(System.currentTimeMillis());
String message = "Sign this message to authenticate: " + nonce;

String signature = client.signMessage(SignMessageOpts.builder()
    .message(message.getBytes(java.nio.charset.StandardCharsets.UTF_8))
    .walletProperties(walletProperties)
    .externalServerKeyShares(externalServerKeyShares)
    .build()
).join();

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Data Integrity

String payloadJson = "{\"userId\":123,\"action\":\"transfer\",\"amount\":\"100\"}";

String signature = client.signMessage(SignMessageOpts.builder()
    .message(payloadJson.getBytes(java.nio.charset.StandardCharsets.UTF_8))
    .walletProperties(walletProperties)
    .externalServerKeyShares(externalServerKeyShares)
    .build()
).join();

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Next Steps