Initial bytes incorrect after Java AES/CBC decryption

Question

What's wrong with the following example? The problem is that the first part of the decrypted string is nonsense. However, the rest is fine, I get... ``` Result: `£eB6O�geS��i are you? Have a nice day. ``` ``` @Test public void testEncrypt() { try { String s = "Hello there. How are you? Have a nice day."; // Generate key KeyGenerator kgen = KeyGenerator.getInstance("AES"); kgen.init(128); SecretKey aesKey = kgen.generateKey(); // Encrypt cipher Cipher encryptCipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); encryptCipher.init(Cipher.ENCRYPT_MODE, aesKey); // Encrypt ByteArrayOutputStream outputStream = new ByteArrayOutputStream(); CipherOutputStream cipherOutputStream = new CipherOutputStream(outputStream, encryptCipher); cipherOutputStream.write(s.getBytes()); cipherOutputStream.flush(); cipherOutputStream.close(); byte[] encryptedBytes = outputStream.toByteArray(); // Decrypt cipher Cipher decryptCipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); IvParameterSpec ivParameterSpec…

Accepted Answer

Lot of people including myself face lot of issues in making this work due to missing some information like, forgetting to convert to Base64, initialization vectors, character set, etc. So I thought of making a fully functional code.

Hope this will be useful to you all: To compile you need additional Apache Commons Codec jar, which is available here: http://commons.apache.org/proper/commons-codec/download_codec.cgi

```
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import org.apache.commons.codec.binary.Base64;

public class Encryptor {
    public static String encrypt(String key, String initVector, String value) {
        try {
            IvParameterSpec iv = new IvParameterSpec(initVector.getBytes("UTF-8"));
            SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes("UTF-8"), "AES");

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
            cipher.init(Cipher.ENCRYPT_MODE, skeySpec, iv);

byte[] encrypted = cipher.doFinal(value.getBytes());
            System.out.println("encrypted string: "
                    + Base64.encodeBase64String(encrypted));

return Base64.encodeBase64String(encrypted);
        } catch (Exception ex) {
            ex.printStackTrace();
        }

return null;
    }

public static String decrypt(String key, String initVector, String encrypted) {
        try {
            IvParameterSpec iv = new IvParameterSpec(initVector.getBytes("UTF-8"));
            SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes("UTF-8"), "AES");

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
            cipher.init(Cipher.DECRYPT_MODE, skeySpec, iv);

byte[] original = cipher.doFinal(Base64.decodeBase64(encrypted));

return new String(original);
        } catch (Exception ex) {
            ex.printStackTrace();
        }

return null;
    }

public static void main(String[] args) {
        String key = "Bar12345Bar12345"; // 128 bit key
        String initVector = "RandomInitVector"; // 16 bytes IV

System.out.println(decrypt(key, initVector,
                encrypt(key, initVector, "Hello World")));
    }
}
```

Initial bytes incorrect after Java AES/CBC decryption

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