数字签名验证失败-Java

Question

I am generating digital signature using below methods with payload as "hello world"

public String generateSignature(String payload) throws Exception{
        Signature rsa = null;
        rsa = Signature.getInstance("SHA256WithRSA/PSS", new BouncyCastleProvider());
        rsa.initSign(getPrivateKey("Keys/private_key"));
        rsa.update(payload.getBytes(StandardCharsets.UTF_8));
        byte[] signatureBytes = Base64.encodeBase64(rsa.sign());
        String signature = DatatypeConverter.printHexBinary(signatureBytes);
        return signature;
    }

I am validating the signature with payload "hello world" and signature that I got from generateSignatue method.

public boolean validateSignature(String payload, String signature) throws Exception {
    Signature sig = Signature.getInstance("SHA256WithRSA/PSS", new BouncyCastleProvider());
    boolean isValid = false;
    sig.initVerify(getPublicKey("Keys/public_key"));                
    sig.update(payload.getBytes(StandardCharsets.UTF_8));
    isValid = sig.verify(Base64.decodeBase64(signature.getBytes("UTF-8")));
    return isValid;
}

This is always returning isValid as false, what is the mistake?

Retrieving Public key & private key with below functions (for reference):

public static PublicKey getPublicKey(String filename) throws Exception {
        byte[] keyBytes = Files.readAllBytes(Paths.get(filename));
        X509EncodedKeySpec spec = new X509EncodedKeySpec(keyBytes);
        KeyFactory kf = KeyFactory.getInstance("RSA");
        return kf.generatePublic(spec);
    }

public static PrivateKey getPrivateKey(String filename) throws Exception {
    byte[] keyBytes = Files.readAllBytes(Paths.get(filename));
    PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(keyBytes);
    KeyFactory kf = KeyFactory.getInstance("RSA");
    return kf.generatePrivate(spec);
}

Answer 1

I can see some errors at a glance:

• A DER file contains certificates, not private keys. Do you have a typo at "Keys/private_key.der" ?

• Your signing code encodes the signature bytes to base64 and hex, but your verification code only decodes from base64. Remove this String signature = DatatypeConverter.printHexBinary(signatureBytes); You can also remove the base64 conversion and work in both methods with byte[] directly

• Within the edited code the hexadecimals is gone, but you need to use base 64 decoding of the signature. Furthermore you must make sure you use a known good base 64 codec, such as Base64.getEncoder() and Base64.getDecoder() .