In this example we will learn how to verify the digital signature of the previously signed data. To sign the data you can see the previous example on this post How to create a digital signature and sign data?.

Here the code snippet:

package org.kodejava.security;

import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.KeyFactory;
import java.security.PublicKey;
import java.security.Signature;
import java.security.spec.X509EncodedKeySpec;

public class VerifyDigitalSignature {
    public static void main(String[] args) {
        try {
            byte[] publicKeyEncoded = Files.readAllBytes(Paths.get("publickey"));
            byte[] digitalSignature = Files.readAllBytes(Paths.get("signature"));

            X509EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(publicKeyEncoded);
            KeyFactory keyFactory = KeyFactory.getInstance("DSA", "SUN");

            PublicKey publicKey = keyFactory.generatePublic(publicKeySpec);
            Signature signature = Signature.getInstance("SHA1withDSA", "SUN");
            signature.initVerify(publicKey);

            byte[] bytes = Files.readAllBytes(Paths.get("README.md"));
            signature.update(bytes);

            boolean verified = signature.verify(digitalSignature);
            if (verified) {
                System.out.println("Data verified.");
            } else {
                System.out.println("Cannot verify data.");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

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Wayan

Founder at Kode Java

Hi, I'm a passionate programmer based on the beautiful island of Bali. I specialize in Java, with hands-on experience in Spring, Hibernate/JPA, and MySQL. I'm currently working on a project I care deeply about, and your support—big or small—helps fuel my work (and my coffee ☕️).

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