AESEncryption.java

packagecom.thealgorithms.ciphers;

importjava.security.InvalidAlgorithmParameterException;
importjava.security.InvalidKeyException;
importjava.security.NoSuchAlgorithmException;
importjavax.crypto.BadPaddingException;
importjavax.crypto.Cipher;
importjavax.crypto.IllegalBlockSizeException;
importjavax.crypto.KeyGenerator;
importjavax.crypto.NoSuchPaddingException;
importjavax.crypto.SecretKey;
importjavax.crypto.spec.GCMParameterSpec;

/**
 * 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.
 */
publicfinalclassAESEncryption {
privateAESEncryption() {
 }

privatestaticfinalchar[] HEX_ARRAY = "0123456789ABCDEF".toCharArray();
privatestaticCipheraesCipher;

/**
 * 1. Generate a plain text for encryption 2. Get a secret key (printed in
 * hexadecimal form). In actual use this must be encrypted and kept safe.
 * The same key is required for decryption.
 */
publicstaticvoidmain(String[] args) throwsException {
StringplainText = "Hello World";
SecretKeysecKey = getSecretEncryptionKey();
byte[] cipherText = encryptText(plainText, secKey);
StringdecryptedText = 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 secKey (Secret key that we encrypt using it)
 * @throws NoSuchAlgorithmException (from KeyGenrator)
 */
publicstaticSecretKeygetSecretEncryptionKey() throwsNoSuchAlgorithmException {
KeyGeneratoraesKeyGenerator = KeyGenerator.getInstance("AES");
aesKeyGenerator.init(128); // The AES key size in number of bits
returnaesKeyGenerator.generateKey();
 }

/**
 * Encrypts plainText in AES using the secret key
 *
 * @return byteCipherText (The encrypted text)
 * @throws NoSuchPaddingException (from Cipher)
 * @throws NoSuchAlgorithmException (from Cipher)
 * @throws InvalidKeyException (from Cipher)
 * @throws BadPaddingException (from Cipher)
 * @throws IllegalBlockSizeException (from Cipher)
 */
publicstaticbyte[] encryptText(StringplainText, SecretKeysecKey) throwsNoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException {
// AES defaults to AES/ECB/PKCS5Padding in Java 7
aesCipher = Cipher.getInstance("AES/GCM/NoPadding");
aesCipher.init(Cipher.ENCRYPT_MODE, secKey);
returnaesCipher.doFinal(plainText.getBytes());
 }

/**
 * Decrypts encrypted byte array using the key used for encryption.
 *
 * @return plainText
 */
publicstaticStringdecryptText(byte[] byteCipherText, SecretKeysecKey) throwsNoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException, InvalidAlgorithmParameterException {
// AES defaults to AES/ECB/PKCS5Padding in Java 7
CipherdecryptionCipher = Cipher.getInstance("AES/GCM/NoPadding");
GCMParameterSpecgcmParameterSpec = newGCMParameterSpec(128, aesCipher.getIV());
decryptionCipher.init(Cipher.DECRYPT_MODE, secKey, gcmParameterSpec);
byte[] bytePlainText = decryptionCipher.doFinal(byteCipherText);
returnnewString(bytePlainText);
 }

/**
 * Convert a binary byte array into readable hex form Old library is
 * deprecated on OpenJdk 11 and this is faster regarding other solution is
 * using StringBuilder
 *
 * @return hexHash
 */
publicstaticStringbytesToHex(byte[] bytes) {
char[] hexChars = newchar[bytes.length * 2];
for (intj = 0; j < bytes.length; j++) {
intv = bytes[j] & 0xFF;
hexChars[j * 2] = HEX_ARRAY[v >>> 4];
hexChars[j * 2 + 1] = HEX_ARRAY[v & 0x0F];
 }
returnnewString(hexChars);
 }
}