Bael 4485 (#10612)

* BAEL-4485 RSA in Java

* BAEL-4485 RSA in Java

* BAEL-4485 RSA in Java

Co-authored-by: majewsk6 <krzysztof.majewski.km1@contractors.roche.com>

core-java-modules/core-java-security-2/src/test/java/com/baeldung/rsa/RsaUnitTest.java

@@ -0,0 +1,92 @@
+package com.baeldung.cipher;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import javax.crypto.Cipher;
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.FileOutputStream;
+import java.io.FileReader;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.security.KeyPair;
+import java.security.KeyPairGenerator;
+import java.security.PrivateKey;
+import java.security.PublicKey;
+
+public class RsaUnitTest {
+
+    @Test
+    public void givenRsaKeyPair_whenEncryptAndDecryptString_thenCompareResults() throws Exception {
+        KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");
+        generator.initialize(2048);
+        KeyPair pair = generator.generateKeyPair();
+        PrivateKey privateKey = pair.getPrivate();
+        PublicKey publicKey = pair.getPublic();
+
+        String secretMessage = "Baeldung secret message";
+        Cipher encryptCipher = Cipher.getInstance("RSA");
+        encryptCipher.init(Cipher.ENCRYPT_MODE, publicKey);
+        byte[] secretMessageBytes = secretMessage.getBytes(StandardCharsets.UTF_8);
+        byte[] encryptedMessageBytes = encryptCipher.doFinal(secretMessageBytes);
+
+        Cipher decryptCipher = Cipher.getInstance("RSA");
+        decryptCipher.init(Cipher.DECRYPT_MODE, privateKey);
+        byte[] decryptedMessageBytes = decryptCipher.doFinal(encryptedMessageBytes);
+        String decryptedMessage = new String(decryptedMessageBytes, StandardCharsets.UTF_8);
+
+        Assertions.assertEquals(secretMessage, decryptedMessage);
+    }
+
+    @Test
+    public void givenRsaKeyPair_whenEncryptAndDecryptFile_thenCompareResults() throws Exception {
+        KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");
+        generator.initialize(2048);
+        KeyPair pair = generator.generateKeyPair();
+        PrivateKey privateKey = pair.getPrivate();
+        PublicKey publicKey = pair.getPublic();
+
+        String originalContent = "some secret message";
+        Path tempFile = Files.createTempFile("temp", "txt");
+        writeString(tempFile, originalContent);
+
+        byte[] fileBytes = Files.readAllBytes(tempFile);
+        Cipher encryptCipher = Cipher.getInstance("RSA");
+        encryptCipher.init(Cipher.ENCRYPT_MODE, publicKey);
+        byte[] encryptedFileBytes = encryptCipher.doFinal(fileBytes);
+        try (FileOutputStream stream = new FileOutputStream(tempFile.toFile())) {
+            stream.write(encryptedFileBytes);
+        }
+
+        encryptedFileBytes = Files.readAllBytes(tempFile);
+        Cipher decryptCipher = Cipher.getInstance("RSA");
+        decryptCipher.init(Cipher.DECRYPT_MODE, privateKey);
+        byte[] decryptedFileBytes = decryptCipher.doFinal(encryptedFileBytes);
+        try (FileOutputStream stream = new FileOutputStream(tempFile.toFile())) {
+            stream.write(decryptedFileBytes);
+        }
+
+        String fileContent = readString(tempFile);
+
+        Assertions.assertEquals(originalContent, fileContent);
+    }
+
+    private void writeString(Path path, String content) throws Exception {
+        try (BufferedWriter writer = Files.newBufferedWriter(path)) {
+            writer.write(content);
+        }
+    }
+
+    private String readString(Path path) throws Exception {
+        StringBuilder resultStringBuilder = new StringBuilder();
+        try (BufferedReader br = new BufferedReader(new FileReader(path.toFile()))) {
+            String line;
+            while ((line = br.readLine()) != null) {
+                resultStringBuilder.append(line);
+            }
+        }
+        return resultStringBuilder.toString();
+    }
+}