BAEL-3282 -- Digital signature. (#7981)

* Digital signature.

* Digital signature.
move message.txt in src/test/resources/digitalsignature.

libraries-security/src/main/java/com/baeldung/digitalsignature/Utils.java

@@ -0,0 +1,33 @@
+package com.baeldung.digitalsignature;
+
+import java.io.FileInputStream;
+import java.security.KeyStore;
+import java.security.PrivateKey;
+import java.security.PublicKey;
+import java.security.cert.Certificate;
+
+public class Utils {
+
+    private static final String STORE_TYPE = "PKCS12";
+    private static final char[] PASSWORD = "changeit".toCharArray();
+    private static final String SENDER_KEYSTORE = "sender_keystore.p12";
+    private static final String SENDER_ALIAS = "senderKeyPair";
+
+    public static final String SIGNING_ALGORITHM = "SHA256withRSA";
+
+    private static final String RECEIVER_KEYSTORE = "receiver_keystore.p12";
+    private static final String RECEIVER_ALIAS = "receiverKeyPair";
+
+    public static PrivateKey getPrivateKey() throws Exception {
+        KeyStore keyStore = KeyStore.getInstance(STORE_TYPE);
+        keyStore.load(new FileInputStream(SENDER_KEYSTORE), PASSWORD);
+        return (PrivateKey) keyStore.getKey(SENDER_ALIAS, PASSWORD);
+    }
+
+    public static PublicKey getPublicKey() throws Exception {
+        KeyStore keyStore = KeyStore.getInstance(STORE_TYPE);
+        keyStore.load(new FileInputStream(RECEIVER_KEYSTORE), PASSWORD);
+        Certificate certificate = keyStore.getCertificate(RECEIVER_ALIAS);
+        return certificate.getPublicKey();
+    }
+}

libraries-security/src/main/java/com/baeldung/digitalsignature/level1/DigitalSignatureWithMessageDigestAndCipherSigning.java

@@ -0,0 +1,28 @@
+package com.baeldung.digitalsignature.level1;
+
+import com.baeldung.digitalsignature.Utils;
+
+import javax.crypto.Cipher;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.security.MessageDigest;
+import java.security.PrivateKey;
+
+public class DigitalSignatureWithMessageDigestAndCipherSigning {
+
+    public static void main(String[] args) throws Exception {
+
+        PrivateKey privateKey = Utils.getPrivateKey();
+
+        byte[] messageBytes = Files.readAllBytes(Paths.get("src/test/resources/digitalsignature/message.txt"));
+
+        MessageDigest md = MessageDigest.getInstance("SHA-256");
+        byte[] messageHash = md.digest(messageBytes);
+
+        Cipher cipher = Cipher.getInstance("RSA");
+        cipher.init(Cipher.ENCRYPT_MODE, privateKey);
+        byte[] digitalSignature = cipher.doFinal(messageHash);
+
+        Files.write(Paths.get("target/digital_signature_1"), digitalSignature);
+    }
+}

libraries-security/src/main/java/com/baeldung/digitalsignature/level1/DigitalSignatureWithMessageDigestAndCipherVerifying.java

@@ -0,0 +1,33 @@
+package com.baeldung.digitalsignature.level1;
+
+import com.baeldung.digitalsignature.Utils;
+
+import javax.crypto.Cipher;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.security.MessageDigest;
+import java.security.PublicKey;
+import java.util.Arrays;
+
+public class DigitalSignatureWithMessageDigestAndCipherVerifying {
+
+    public static void main(String[] args) throws Exception {
+
+        PublicKey publicKey = Utils.getPublicKey();
+
+        byte[] messageBytes = Files.readAllBytes(Paths.get("src/test/resources/digitalsignature/message.txt"));
+
+        MessageDigest md = MessageDigest.getInstance("SHA-256");
+        byte[] newMessageHash = md.digest(messageBytes);
+
+        byte[] encryptedMessageHash = Files.readAllBytes(Paths.get("target/digital_signature_1"));
+
+        Cipher cipher = Cipher.getInstance("RSA");
+        cipher.init(Cipher.DECRYPT_MODE, publicKey);
+        byte[] decryptedMessageHash = cipher.doFinal(encryptedMessageHash);
+
+        boolean isCorrect = Arrays.equals(decryptedMessageHash, newMessageHash);
+        System.out.println("Signature " + (isCorrect ? "correct" : "incorrect"));
+    }
+
+}

libraries-security/src/main/java/com/baeldung/digitalsignature/level2/DigitalSignatureWithSignatureSigning.java

@@ -0,0 +1,27 @@
+package com.baeldung.digitalsignature.level2;
+
+import com.baeldung.digitalsignature.Utils;
+
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.security.PrivateKey;
+import java.security.Signature;
+
+public class DigitalSignatureWithSignatureSigning {
+
+    public static void main(String[] args) throws Exception {
+
+        PrivateKey privateKey = Utils.getPrivateKey();
+
+        Signature signature = Signature.getInstance(Utils.SIGNING_ALGORITHM);
+        signature.initSign(privateKey);
+
+        byte[] messageBytes = Files.readAllBytes(Paths.get("src/test/resources/digitalsignature/message.txt"));
+
+        signature.update(messageBytes);
+        byte[] digitalSignature = signature.sign();
+
+        Files.write(Paths.get("target/digital_signature_2"), digitalSignature);
+    }
+
+}

libraries-security/src/main/java/com/baeldung/digitalsignature/level2/DigitalSignatureWithSignatureVerifying.java

@@ -0,0 +1,28 @@
+package com.baeldung.digitalsignature.level2;
+
+import com.baeldung.digitalsignature.Utils;
+
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.security.PublicKey;
+import java.security.Signature;
+
+public class DigitalSignatureWithSignatureVerifying {
+
+    public static void main(String[] args) throws Exception {
+
+        PublicKey publicKey = Utils.getPublicKey();
+
+        byte[] sig = Files.readAllBytes(Paths.get("target/digital_signature_2"));
+
+        Signature signature = Signature.getInstance(Utils.SIGNING_ALGORITHM);
+        signature.initVerify(publicKey);
+
+        byte[] messageBytes = Files.readAllBytes(Paths.get("src/test/resources/digitalsignature/message.txt"));
+
+        signature.update(messageBytes);
+
+        boolean isCorrect = signature.verify(sig);
+        System.out.println("Signature " + (isCorrect ? "correct" : "incorrect"));
+    }
+}

libraries-security/src/test/resources/digitalsignature/message.txt

@@ -0,0 +1 @@
+This is a cool message!