There are many ways to encrypt and decrypt String in java. I will discuss how to encrypt or decrypt data using  Cipher class. Cipher class is the part of Java Cryptographic Extension (JCE) framework.

The Cipher class is part of javax.crypto package.

How it works?

Encryption = cleartext + secret key +AES algorithm = ciphertext(encrypted text)

Decryption = ciphertext + secret key +AES algorithm = cleartext

Types of encryption

1. Symmetric

   Same secret key for encryption and decryption.

2. Asymmetric

   Public/private key pair for encryption and decryption, encryption with public key and decryption with same pare private key example – RSA

Typers of ciphers

1. Block Cipher

   Process entire block at a time.

2. Stream Cipher

   Process incoming data unit by unit, unit size can be 1 byte or a bit.

Standard Cipher implementations.

Cipher object can be created from the below implementations.

Algorithm/mode/padding (key size)

AES/CBC/NoPadding (128)
AES/CBC/PKCS5Padding (128)
AES/ECB/NoPadding (128)
AES/ECB/PKCS5Padding (128)
DES/CBC/NoPadding (56)
DES/CBC/PKCS5Padding (56)
DES/ECB/NoPadding (56)
DES/ECB/PKCS5Padding (56)
DESede/CBC/NoPadding (168)
DESede/CBC/PKCS5Padding (168)
DESede/ECB/NoPadding (168)
DESede/ECB/PKCS5Padding (168)
RSA/ECB/PKCS1Padding (1024, 2048)
RSA/ECB/OAEPWithSHA-1AndMGF1Padding (1024, 2048)
RSA/ECB/OAEPWithSHA-256AndMGF1Padding (1024, 2048)

AES– Advanced Encryption Standard
DES – Data Encryption Standard
DESede – (3DES) Triple DES
RSA – Rivest-Shamir-Adleman
CBC– cipher block chaining
ECB – electronic code book

How to create cipher Object?

Cipher cipherObject = Cipher.getInstance(“DES/CBC/PKCS5Padding”);

Modes of cipher object

1. ENCRYPT_MODE – data encryption
2. DECRYPT_MODE – decrypt the encrypted data.
3. WRAP_MODE – wrap the key into byte to transport securely.
4. UNWRAP_MODE – Unwrap the wrap key into java object.

Sample Code

EncryptionDecryption .java

package com.javaant;

public class EncryptionDecryption {

public static void main(String args[]) {
    
    System.out.println("string after encription of (Nirmal Dhara)  ::   "+CipherUtils.getEncryptedString("Nirmal Dhara"));
    System.out.println("String after decription of (8TymgE7S7Px6uZXScZlrRQ==) ::  "+CipherUtils.getDecriyptedString("8TymgE7S7Px6uZXScZlrRQ=="));

  }

}

CipherUtils .java

package com.javaant;

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

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

public class CipherUtils {

  private static byte[] key = { 0x24, 0x68, 0x78, 0x71, 0x49, 0x73, 0x41,
    0x24, 0x28, 0x78, 0x41, 0x49, 0x63, 0x41,0x73, 0x9};// "this Is A SecretKey you can change it, size is 16";

  public static String encrypt(String strToEncrypt) {
    try {
      Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING");
      final SecretKeySpec secretKey = new SecretKeySpec(key, "AES");
      cipher.init(Cipher.ENCRYPT_MODE, secretKey);
      final String encryptedString = Base64.encodeBase64String(cipher
          .doFinal(strToEncrypt.getBytes()));
      return encryptedString;
    } catch (Exception e) {
      e.printStackTrace();
    }
    return null;

  }

  public static String decrypt(String strToDecrypt) {
    try {
      Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING");
      final SecretKeySpec secretKey = new SecretKeySpec(key, "AES");
      cipher.init(Cipher.DECRYPT_MODE, secretKey);
      final String decryptedString = new String(cipher.doFinal(Base64.decodeBase64(strToDecrypt)));
      return decryptedString;
    } catch (Exception e) {
      e.printStackTrace();

    }
    return null;
  }

  public static String getEncryptedString(String str) {
    final String strToEncrypt = str;
    final String encryptedStr = CipherUtils.encrypt(strToEncrypt.trim());

    return encryptedStr;
  }

  public static String getDecriyptedString(String str) {
    final String strToDecrypt = str;
    final String decryptedStr = CipherUtils.decrypt(strToDecrypt.trim());

    return decryptedStr;
  }

  
}