Verifying ethereum message signatures with java

Question

I am using web3j to verify message signatures but there are some false negative results.

For example this signature should be right, but it seems like the address could not be recovered:

     final String address = "0x638aF69053892CDD7Ad295fC2482d1a11Fe5a9B7";
     final String signature = "0x6c26935cc03e4e93c0bd1c3d068a54eb961bbc7db4ecf6c7b55b5b9bb073d32b61fcabeabd028322401ea62202726b520b84fd27aa7f8a8050dff728e064cebf1c";
     final String message = "5893";

    boolean isSignatureValid(final String address, final String signature, final String message) {
        log.info("isSignatureValid invoked for Address {} with Signature {} and Message {} ", address, signature,
                message);

        final String personalMessagePrefix = "\u0019Ethereum Signed Message:\n";
        boolean match = false;

        final String prefix = personalMessagePrefix + message.length();
        final byte[] msgHash = Hash.sha3((prefix + message).getBytes());
        final byte[] signatureBytes = Numeric.hexStringToByteArray(signature);
        byte v = signatureBytes[64];
        if (v < 27) {
            v += 27;
        }

        final SignatureData sd = new SignatureData(v,
                Arrays.copyOfRange(signatureBytes, 0, 32),
                Arrays.copyOfRange(signatureBytes, 32, 64));

        String addressRecovered = null;

        // Iterate for each possible key to recover
        for (int i = 0; i < 4; i++) {
            final BigInteger publicKey = Sign.recoverFromSignature((byte) i, new ECDSASignature(
                            new BigInteger(1, sd.getR()),
                            new BigInteger(1, sd.getS())), msgHash);

            if (publicKey != null) {
                addressRecovered = "0x" + Keys.getAddress(publicKey);

                if (addressRecovered.equals(address)) {
                    match = true;
                    break;
                }
            }
        }

        return match;
    }
}

I am still new in this area.

Answer 1

This should help you:

public static String getAddressUsedToSignHashedMessage(String signedHash, String originalMessageHashInHex) throws SignatureException {
        byte[] messageHashBytes = Numeric.hexStringToByteArray(originalMessageHashInHex);
        String r = signedHash.substring(0, 66);
        String s = "0x"+signedHash.substring(66, 130);
        String v = "0x"+signedHash.substring(130, 132);
        System.out.println();
        byte[] msgBytes = new byte[GETH_SIGN_PREFIX.getBytes().length + messageHashBytes.length];
        byte[] prefixBytes = GETH_SIGN_PREFIX.getBytes();
        System.arraycopy(prefixBytes, 0, msgBytes, 0, prefixBytes.length);
        System.arraycopy(messageHashBytes, 0, msgBytes, prefixBytes.length, messageHashBytes.length);
        String pubkey = Sign.signedMessageToKey(msgBytes,
                new Sign.SignatureData(Numeric.hexStringToByteArray(v)[0],
                        Numeric.hexStringToByteArray(r),
                        Numeric.hexStringToByteArray(s)))
                .toString(16);
        System.out.println("");
        System.out.println("Pubkey: " + pubkey);
        String address = Keys.getAddress(pubkey);
        return address;
    }

Reference: https://gist.github.com/megamattron/94c05789e5ff410296e74dad3b528613