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import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.xml.bind.DatatypeConverter;
/**
* This example program shows how AES encryption and decryption can be done in Java.
* Please note that secret key and encrypted text is unreadable binary and hence
* in the following program we display it in hexadecimal format of the underlying bytes.
*/
public class AESEncryption {
/**
* 1. Generate a plain text for encryption
* 2. Get a secret key (printed in hexadecimal form). In actual use this must
* by encrypted and kept safe. The same key is required for decryption.
*
*/
public static void main(String[] args) throws Exception {
String plainText = "Hello World";
SecretKey secKey = getSecretEncryptionKey();
byte[] cipherText = encryptText(plainText, secKey);
String decryptedText = decryptText(cipherText, secKey);
System.out.println("Original Text:" + plainText);
System.out.println("AES Key (Hex Form):"+bytesToHex(secKey.getEncoded()));
System.out.println("Encrypted Text (Hex Form):"+bytesToHex(cipherText));
System.out.println("Descrypted Text:"+decryptedText);
}
/**
* gets the AES encryption key. In your actual programs, this should be safely
* stored.
* @return
* @throws Exception
*/
public static SecretKey getSecretEncryptionKey() throws Exception{
KeyGenerator generator = KeyGenerator.getInstance("AES");
generator.init(128); // The AES key size in number of bits
SecretKey secKey = generator.generateKey();
return secKey;
}
/**
* Encrypts plainText in AES using the secret key
* @param plainText
* @param secKey
* @return
* @throws Exception
*/
public static byte[] encryptText(String plainText,SecretKey secKey) throws Exception{
// AES defaults to AES/ECB/PKCS5Padding in Java 7
Cipher aesCipher = Cipher.getInstance("AES");
aesCipher.init(Cipher.ENCRYPT_MODE, secKey);
byte[] byteCipherText = aesCipher.doFinal(plainText.getBytes());
return byteCipherText;
}
/**
* Decrypts encrypted byte array using the key used for encryption.
* @param byteCipherText
* @param secKey
* @return
* @throws Exception
*/
public static String decryptText(byte[] byteCipherText, SecretKey secKey) throws Exception {
// AES defaults to AES/ECB/PKCS5Padding in Java 7
Cipher aesCipher = Cipher.getInstance("AES");
aesCipher.init(Cipher.DECRYPT_MODE, secKey);
byte[] bytePlainText = aesCipher.doFinal(byteCipherText);
return new String(bytePlainText);
}
/**
* Convert a binary byte array into readable hex form
* @param hash
* @return
*/
private static String bytesToHex(byte[] hash) {
return DatatypeConverter.printHexBinary(hash);
}
}