signature.verify() Always returns False

Question

 public static void main(String[] args) {
    try{
        String mod = "q0AwozeUj0VVkoksDQSCTj3QEgODomq4sAr02xMyIrWldZrNHhWfZAIcWt2MuAY3X6S3ZVUfOFXOrVbltRrO3F9Z6R8/jJIMv7wjkeVBFC5gncwGR0C3aV9gmF6II19jTKfF1sxb26iMEMAlMEOSnAAceNaJH91zBoaW7ZIh+qk=";
        String exp = "AQAB";
        byte[] modulusBytes = Base64.decodeBase64(mod.getBytes("UTF-8"));
        byte[] exponentBytes = Base64.decodeBase64(exp.getBytes("UTF-8"));
        String signedMessage = "3753e672cfb21e3c182ef2df51f19edeffb63432ed338a47251326ccc14aa63883e910a140cf313754ebc6425aad434e309307cc882da6cd4a4f9f40bd14a9823aca145e5ffc97cd63dbb5925c049282416bdfd7d74ddeef7055065210a841793fe315dff5a44af19c1522daafdc2f7e61ce5a2b42ebf79dfb086e6d210168dd";
        BigInteger modulus = new BigInteger(1, modulusBytes );               
        BigInteger exponent = new BigInteger(1, exponentBytes);
        RSAPublicKeySpec rsaPubKey = new RSAPublicKeySpec(modulus, exponent);
        KeyFactory fact = KeyFactory.getInstance("RSA");
        PublicKey pubKey = fact.generatePublic(rsaPubKey);
        Signature signature = Signature.getInstance("SHA1withRSA");
        byte[] sigBytes = hexStringToByteArray(signedMessage);
        signature.initVerify(pubKey);
        System.out.println(signature.verify(sigBytes));
    }catch(Exception e){
        System.out.println("Error: " + e.toString());
    }
}
private static byte[] hexStringToByteArray(final String encoded) {
    if ((encoded.length() % 2) != 0)
        throw new IllegalArgumentException("Input string must contain an even number of characters");

    final byte result[] = new byte[encoded.length()/2];
    final char enc[] = encoded.toCharArray();
    for (int i = 0; i < enc.length; i += 2) {
        StringBuilder curr = new StringBuilder(2);
        curr.append(enc[i]).append(enc[i + 1]);
        result[i/2] = (byte) Integer.parseInt(curr.toString(), 16);
    }
    return result;
}

This code always returns false. I'm not sure where to go from here.

Answer 1

Where you sign the message you should have some code like this:

Signature signature = Signature.getInstance("SHA1withRSA");
signature.initSign(privKey);
signature.update(message);
byte[] signatureValue = signature.sign();

Note the byte-array named signatureValue. That is the actual signature on the data. That is what you should provide to the verify()-method. The message that is signed should be provided in a call to the update()-method. I.e.:

Signature signature = Signature.getInstance("SHA1withRSA");
signature.initVerify(pubKey);
signature.update(message);
bool ok = signature.verify(signatureValue);