Symetric: Encryption and decryption by same key

Symmetric encryption uses the same key for both encryption and decryption. This is different from asymmetric encryption where different keys are used. A common algorithm for symmetric encryption is AES (Advanced Encryption Standard).

Example of Symmetric Encryption and Decryption in Java Using AES

Here’s an example that demonstrates how to perform symmetric encryption and decryption using AES in Java:

Maven Dependency

Ensure you have the following dependency in your pom.xml if you're using Maven:

xml

<groupId>org.bouncycastle</groupId>

<artifactId>bcprov-jdk15on</artifactId>

</dependency>

Java Code Example

java

import javax.crypto.Cipher;

import javax.crypto.KeyGenerator;

import javax.crypto.SecretKey;

import javax.crypto.spec.IvParameterSpec;

import java.security.SecureRandom;

import java.util.Base64;

public class AESEncryption {

// Generate a new AES key

public static SecretKey generateKey(int n) throws Exception {

KeyGenerator keyGen = KeyGenerator.getInstance("AES");

keyGen.init(n);

return keyGen.generateKey();

}

// Generate a new initialization vector (IV)

public static IvParameterSpec generateIv() {

byte[] iv = new byte[16];

new SecureRandom().nextBytes(iv);

return new IvParameterSpec(iv);

}

// Encrypt the input string using the provided key and IV

public static String encrypt(String input, SecretKey key, IvParameterSpec iv) throws Exception {

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

cipher.init(Cipher.ENCRYPT_MODE, key, iv);

byte[] cipherText = cipher.doFinal(input.getBytes());

return Base64.getEncoder().encodeToString(cipherText);

}

// Decrypt the input string using the provided key and IV

public static String decrypt(String cipherText, SecretKey key, IvParameterSpec iv) throws Exception {

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

cipher.init(Cipher.DECRYPT_MODE, key, iv);

byte[] plainText = cipher.doFinal(Base64.getDecoder().decode(cipherText));

return new String(plainText);

}

public static void main(String[] args) {

try {

// Generate AES key

SecretKey key = generateKey(256);

// Generate IV

IvParameterSpec iv = generateIv();

// Data to be encrypted

String input = "Hello, World!";

// Encrypt the data

String cipherText = encrypt(input, key, iv);

System.out.println("Encrypted Text: " + cipherText);

// Decrypt the data

String plainText = decrypt(cipherText, key, iv);

System.out.println("Decrypted Text: " + plainText);

} catch (Exception e) {

e.printStackTrace();

}

Explanation

Key Generation:

The generateKey method generates a new AES key. The parameter n specifies the key size, typically 128, 192, or 256 bits. In this example, 256-bit AES is used.

IV Generation:

The generateIv method generates a new initialization vector (IV) which is required for AES in CBC mode. The IV ensures that the same plaintext encrypted multiple times will yield different ciphertexts.

Encryption:

The encrypt method initializes the cipher in encryption mode using the AES key and IV. It then encrypts the input string and returns the ciphertext encoded in Base64.

Decryption:

The decrypt method initializes the cipher in decryption mode using the same AES key and IV. It then decrypts the Base64 encoded ciphertext back into plaintext.

Main Method:

The main method demonstrates the full encryption and decryption process. It generates an AES key and IV, encrypts a sample string, and then decrypts the ciphertext back to the original plaintext.

Notes

Key Management: The security of symmetric encryption depends on keeping the key secret. Ensure that the key is stored securely and not exposed.
IV Usage: The IV should be unique for each encryption operation. For CBC mode, the IV does not need to be secret but must be unique and can be sent along with the ciphertext.
Algorithm Variants: The example uses AES/CBC/PKCS5Padding. Depending on the use case, other modes and padding schemes might be required, such as GCM mode for authenticated encryption.

This example provides a straightforward way to implement AES-based symmetric encryption and decryption in Java, ensuring that data can be securely encrypted and decrypted using the same key.

Example of Symmetric Encryption and Decryption in Java Using DES

DES (Data Encryption Standard) is a symmetric-key algorithm used for the encryption and decryption of data. DES operates on 64-bit blocks of data and uses a 56-bit key.

Although DES is considered outdated and insecure for many applications today due to its short key length and susceptibility to brute-force attacks, it's still valuable for understanding the basics of symmetric encryption.

Here’s an example in Java that demonstrates how to perform symmetric encryption and decryption using DES:

Maven Dependency

Make sure you have the following dependency in your pom.xml if you're using Maven:

xml

<groupId>org.bouncycastle</groupId>

<artifactId>bcprov-jdk15on</artifactId>

</dependency>

Java Code Example

Key Generation

java

import javax.crypto.KeyGenerator;

import javax.crypto.SecretKey;

public class DESKeyGenerator {

public static SecretKey generateKey() throws Exception {

KeyGenerator keyGen = KeyGenerator.getInstance("DES");

keyGen.init(56); // DES uses a 56-bit key size

return keyGen.generateKey();

}

Encryption and Decryption

java

import javax.crypto.Cipher;

import javax.crypto.SecretKey;

import javax.crypto.spec.IvParameterSpec;

import java.security.SecureRandom;

import java.util.Base64;

import java.nio.file.Files;

import java.nio.file.Paths;

public class DESEncryption {

// Generate a new initialization vector (IV)

public static IvParameterSpec generateIv() {

byte[] iv = new byte[8]; // DES uses an 8-byte block size

new SecureRandom().nextBytes(iv);

return new IvParameterSpec(iv);

}

// Encrypt the input string using the provided key and IV

public static String encrypt(String input, SecretKey key, IvParameterSpec iv) throws Exception {

Cipher cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");

cipher.init(Cipher.ENCRYPT_MODE, key, iv);

byte[] cipherText = cipher.doFinal(input.getBytes());

return Base64.getEncoder().encodeToString(cipherText);

}

// Decrypt the input string using the provided key and IV

public static String decrypt(String cipherText, SecretKey key, IvParameterSpec iv) throws Exception {

Cipher cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");

cipher.init(Cipher.DECRYPT_MODE, key, iv);

byte[] plainText = cipher.doFinal(Base64.getDecoder().decode(cipherText));

return new String(plainText);

}

public static void main(String[] args) {

try {

// Generate DES key

SecretKey key = DESKeyGenerator.generateKey();

// Generate IV

IvParameterSpec iv = generateIv();

// Data to be encrypted

String input = "Hello, World!";

// Encrypt the data

String cipherText = encrypt(input, key, iv);

System.out.println("Encrypted Text: " + cipherText);

// Decrypt the data

String plainText = decrypt(cipherText, key, iv);

System.out.println("Decrypted Text: " + plainText);

} catch (Exception e) {

e.printStackTrace();

}

Explanation

Key Generation:

The generateKey method generates a DES key. DES uses a 56-bit key size.
KeyGenerator.getInstance("DES") initializes the key generator with the DES algorithm.
keyGen.init(56) sets the key size to 56 bits.

IV Generation:

The generateIv method generates an initialization vector (IV), which is required for DES in CBC mode. The IV ensures that the same plaintext encrypted multiple times will yield different ciphertexts.

Encryption:

The encrypt method initializes the cipher in encryption mode using the DES key and IV.
Cipher.getInstance("DES/CBC/PKCS5Padding") initializes the cipher with DES algorithm, CBC mode, and PKCS5 padding.
cipher.init(Cipher.ENCRYPT_MODE, key, iv) initializes the cipher for encryption mode.
cipher.doFinal(input.getBytes()) performs the encryption and returns the encrypted byte array, which is then encoded to a Base64 string.

Decryption:

The decrypt method initializes the cipher in decryption mode using the same DES key and IV.
Cipher.getInstance("DES/CBC/PKCS5Padding") initializes the cipher with DES algorithm, CBC mode, and PKCS5 padding.
cipher.init(Cipher.DECRYPT_MODE, key, iv) initializes the cipher for decryption mode.
cipher.doFinal(Base64.getDecoder().decode(cipherText)) performs the decryption and returns the original byte array, which is then converted to a string.

Main Method:

The main method demonstrates the full encryption and decryption process. It generates a DES key and IV, encrypts a sample string, and then decrypts the ciphertext back to the original plaintext.

Notes

Key Management: The security of symmetric encryption depends on keeping the key secret. Ensure that the key is stored securely and not exposed.
IV Usage: The IV should be unique for each encryption operation. For CBC mode, the IV does not need to be secret but must be unique and can be sent along with the ciphertext.
Algorithm and Padding: The example uses DES/CBC/PKCS5Padding. Depending on your security requirements, other modes and padding schemes might be required.

This example provides a straightforward way to implement DES-based symmetric encryption and decryption in Java, ensuring that data can be securely encrypted and decrypted using the same key.