Encrypting String with Java

Question

I am trying to encrypt and decrypt a String by using Java and AES Cipher.getInstance("AES/CBC/PKCS5PADDING").

When I encrypt the data and try to print it to the console, I am getting characters something like this :

�0��J�9U\�6N��.��͋«D�<(��H(�G�jַ��%��u��^� ��'�bT/�05��0+u)b�ς�{G�d��/�:��~��ٵ�J%��~_��_��~�W�s�+]9�{Y�N��J{��釔Ä��

Is this correct? Can be said "it is encrypted"? My expectation was to get literal String like "WERWERWERWER"

Thats because encrypted messege is in bytes(0-255). To get string like you want you need to encode output with base 64. — Mateusz, Jan 05 '18 at 17:14
Yes, there's really no such concept of "encrypting a String". You encrypt *bytes* into other bytes, and the result most likely won't be very display friendly. If you're just trying to convert letters to other letters, then use something like [Caesar cipher](https://en.wikipedia.org/wiki/Caesar_cipher). — Kayaman, Jan 05 '18 at 17:18
@Kayaman "use something like Caesar cipher": but only if you are happy with kindergarten strength security — Henry, Jan 05 '18 at 17:20
@Henry well, his expectation *was* to get a String like "WERWERWER"... — Kayaman, Jan 05 '18 at 17:20

Mateusz · Accepted Answer · 2018-01-05T17:25:04.943

5

Thats because encrypted message is in bytes(0-255). To get string like you want you need to encode output with base 64.

Based on this answer you can do that in Java 8 without using any libraries.

import java.util.Base64;

//base64 encoding
byte[] encodedBytes = Base64.getEncoder().encode("Test".getBytes("UTF-8"));
System.out.println("encodedBytes " + new String(encodedBytes));
//base64 decoding
byte[] decodedBytes = Base64.getDecoder().decode(encodedBytes);
System.out.println("decodedBytes " + new String(decodedBytes));

Replace "Test".getBytes("UTF-8") with output from AES

edited Jan 05 '18 at 17:25

answered Jan 05 '18 at 17:19

Mateusz

681
5
9

2

Always specify the encoding, so `.getBytes("UTF-8");` for example. – Kayaman Jan 05 '18 at 17:21
I updated answer. This is just a sample, and OP already has his bytes ready. – Mateusz Jan 05 '18 at 17:23
4

It's important to make sure samples are proper. Many people don't understand the significance of specifying the encoding, and that causes a lot of confusion when it ends up biting them in the behind. – Kayaman Jan 05 '18 at 17:25
Use constants in `StandardCharsets` to specify common encodings. For example, `str.getBytes(StandardCharsets.UTF_8)`. – erickson Jan 05 '18 at 20:29

score 0 · Answer 2 · answered Jan 05 '18 at 17:54

Just use the UTF-8 encoding and your values should be right.

I've just made an small example so I think will be clear to understand.

Please check here:

package com.nicolas.cli;

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.security.GeneralSecurityException;
import java.security.Key;
import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

public class TestCrypt {

  public static void main(String args[]) {

    TestCrypt testCrypt = new TestCrypt(keyValue);
    String encrypted = testCrypt.encrypt("someValue");
    System.out.println(encrypted);
    String decrypted = testCrypt.decrypt(encrypted);
    System.out.println(decrypted);

  }

  private static final String CRYPTO_ALGORITHM = "AES";
  private static final Logger LOGGER = LoggerFactory.getLogger(TestCrypt.class);
  private static final byte[] keyValue =
      new byte[]{'T', 'h', 'e', 'B', 'e', 's', 't', 'S', 'e', 'c', 'r', 'e', 't', 'K', 'e', 'y'};


  private final Key key;
  private final Cipher cipher = getCipherInstance();

  public TestCrypt(byte [] key) {
    this.key = new SecretKeySpec(key, CRYPTO_ALGORITHM);
  }

  private Cipher getCipherInstance() {
    try {
      return Cipher.getInstance(CRYPTO_ALGORITHM);
    } catch (GeneralSecurityException e) {
      LOGGER.error("Crypto error: Unable to get cipher instance");
      throw new RuntimeException(e);
    }
  }

  public String encrypt(String password) {
    try {
      cipher.init(Cipher.ENCRYPT_MODE, key);
      byte[] encVal = cipher.doFinal(password.getBytes());
      return new BASE64Encoder().encode(encVal);
    } catch (GeneralSecurityException e) {
      LOGGER.error("Crypto error: Unable to encrypt password");
      throw new RuntimeException(e);
    }
  }

  public String decrypt(String encryptedPassword) {
    try {
      cipher.init(Cipher.DECRYPT_MODE, key);
      byte[] decodedValue = new BASE64Decoder().decodeBuffer(encryptedPassword);
      return new String(cipher.doFinal(decodedValue), StandardCharsets.UTF_8);
    } catch (GeneralSecurityException | IOException e) {
      LOGGER.error("Crypto error: Unable to encrypt password");
      throw new RuntimeException(e);
    }
  }

}

Your description is incorrect, but your code does it correctly by base64-encoding the bytes returned by the encryption. Unfortunately you use an unsupported base-64 encoder/decoder in your code. — President James K. Polk, Jan 05 '18 at 18:19

Encrypting String with Java

2 Answers2