From c0aaed7474a01ccac78a71a82b9448856408d3a2 Mon Sep 17 00:00:00 2001
From: Kevin Wittek <kevin.wittek@styracosoft.de>
Date: Sun, 1 Jul 2018 21:05:28 +0200
Subject: [PATCH] [BAEL-1930] Encryption and decryption of files using JDK

---
 .gitmodules                                   |  3 -
 .../encrypt/FileEncrypterDecrypter.java       | 61 +++++++++++++++++++
 ...FileEncrypterDecrypterIntegrationTest.java | 33 ++++++++++
 3 files changed, 94 insertions(+), 3 deletions(-)
 delete mode 100644 .gitmodules
 create mode 100644 core-java/src/main/java/com/baeldung/encrypt/FileEncrypterDecrypter.java
 create mode 100644 core-java/src/test/java/com/baeldung/encrypt/FileEncrypterDecrypterIntegrationTest.java

diff --git a/.gitmodules b/.gitmodules
deleted file mode 100644
index 9c5cdb8f2d..0000000000
--- a/.gitmodules
+++ /dev/null
@@ -1,3 +0,0 @@
-[submodule "testgitrepo"]
-	path = testgitrepo
-	url = /home/prd/Development/projects/idea/tutorials/spring-boot/src/main/resources/testgitrepo/
diff --git a/core-java/src/main/java/com/baeldung/encrypt/FileEncrypterDecrypter.java b/core-java/src/main/java/com/baeldung/encrypt/FileEncrypterDecrypter.java
new file mode 100644
index 0000000000..aad2089d8b
--- /dev/null
+++ b/core-java/src/main/java/com/baeldung/encrypt/FileEncrypterDecrypter.java
@@ -0,0 +1,61 @@
+package com.baeldung.encrypt;
+
+import javax.crypto.*;
+import javax.crypto.spec.IvParameterSpec;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+
+class FileEncrypterDecrypter {
+
+    private SecretKey secretKey;
+    private Cipher cipher;
+
+    FileEncrypterDecrypter(SecretKey secretKey, String cipher) throws NoSuchPaddingException, NoSuchAlgorithmException {
+        this.secretKey = secretKey;
+        this.cipher = Cipher.getInstance(cipher);
+    }
+
+    void encrypt(String content, String fileName) throws InvalidKeyException, IOException {
+        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
+        byte[] iv = cipher.getIV();
+
+        try (
+                FileOutputStream fileOut = new FileOutputStream(fileName);
+                CipherOutputStream cipherOut = new CipherOutputStream(fileOut, cipher)
+        ) {
+            fileOut.write(iv);
+            cipherOut.write(content.getBytes());
+        }
+
+    }
+
+    String decrypt(String fileName) throws InvalidAlgorithmParameterException, InvalidKeyException, IOException {
+
+        String content;
+
+        try (FileInputStream fileIn = new FileInputStream(fileName)) {
+            byte[] fileIv = new byte[16];
+            fileIn.read(fileIv);
+            cipher.init(Cipher.DECRYPT_MODE, secretKey, new IvParameterSpec(fileIv));
+
+            try (CipherInputStream cipherIn = new CipherInputStream(fileIn, cipher)) {
+                InputStreamReader inReader = new InputStreamReader(cipherIn);
+
+                StringBuilder sb = new StringBuilder();
+                int c = inReader.read();
+                while (c != -1) {
+                    sb.append((char) c);
+                    c = inReader.read();
+                }
+                content = sb.toString();
+            }
+
+        }
+        return content;
+    }
+}
diff --git a/core-java/src/test/java/com/baeldung/encrypt/FileEncrypterDecrypterIntegrationTest.java b/core-java/src/test/java/com/baeldung/encrypt/FileEncrypterDecrypterIntegrationTest.java
new file mode 100644
index 0000000000..6cadfcde1d
--- /dev/null
+++ b/core-java/src/test/java/com/baeldung/encrypt/FileEncrypterDecrypterIntegrationTest.java
@@ -0,0 +1,33 @@
+package com.baeldung.encrypt;
+
+import org.junit.Test;
+
+import javax.crypto.KeyGenerator;
+import javax.crypto.NoSuchPaddingException;
+import javax.crypto.SecretKey;
+import java.io.File;
+import java.io.IOException;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+
+import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.assertThat;
+
+public class FileEncrypterDecrypterIntegrationTest {
+
+    @Test
+    public void givenStringAndFilename_whenEncryptingIntoFile_andDecryptingFileAgain_thenOriginalStringIsReturned() throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IOException, InvalidAlgorithmParameterException {
+        String originalContent = "foobar";
+        SecretKey secretKey = KeyGenerator.getInstance("AES").generateKey();
+
+        FileEncrypterDecrypter fileEncrypterDecrypter = new FileEncrypterDecrypter(secretKey, "AES/CBC/PKCS5Padding");
+        fileEncrypterDecrypter.encrypt(originalContent, "baz.enc");
+
+        String decryptedContent = fileEncrypterDecrypter.decrypt("baz.enc");
+        assertThat(decryptedContent, is(originalContent));
+
+        new File("baz.enc").delete(); // cleanup
+    }
+
+}
\ No newline at end of file