126 lines
4.3 KiB
Java
126 lines
4.3 KiB
Java
package ciphers;
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import java.security.InvalidKeyException;
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import java.security.NoSuchAlgorithmException;
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import javax.crypto.BadPaddingException;
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import javax.crypto.Cipher;
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import javax.crypto.IllegalBlockSizeException;
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import javax.crypto.KeyGenerator;
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import javax.crypto.NoSuchPaddingException;
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import javax.crypto.SecretKey;
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/**
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* This example program shows how AES encryption and decryption can be done in
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* Java. Please note that secret key and encrypted text is unreadable binary and
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* hence in the following program we display it in hexadecimal format of the
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* underlying bytes.
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*
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*/
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public class AESEncryption {
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private static final char[] HEX_ARRAY = "0123456789ABCDEF".toCharArray();
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/**
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* 1. Generate a plain text for encryption 2. Get a secret key (printed in
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* hexadecimal form). In actual use this must by encrypted and kept safe. The
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* same key is required for decryption.
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*
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*/
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public static void main(String[] args) throws Exception {
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String plainText = "Hello World";
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SecretKey secKey = getSecretEncryptionKey();
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byte[] cipherText = encryptText(plainText, secKey);
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String decryptedText = decryptText(cipherText, secKey);
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System.out.println("Original Text:" + plainText);
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System.out.println("AES Key (Hex Form):" + bytesToHex(secKey.getEncoded()));
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System.out.println("Encrypted Text (Hex Form):" + bytesToHex(cipherText));
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System.out.println("Descrypted Text:" + decryptedText);
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}
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/**
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* gets the AES encryption key. In your actual programs, this should be safely
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* stored.
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*
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* @return secKey (Secret key that we encrypt using it)
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* @throws NoSuchAlgorithmException
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* (from KeyGenrator)
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*
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*/
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public static SecretKey getSecretEncryptionKey() throws NoSuchAlgorithmException {
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KeyGenerator aesKeyGenerator = KeyGenerator.getInstance("AES");
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aesKeyGenerator.init(128); // The AES key size in number of bits
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SecretKey secKey = aesKeyGenerator.generateKey();
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return secKey;
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}
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/**
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* Encrypts plainText in AES using the secret key
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*
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* @param plainText
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* @param secKey
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* @return byteCipherText (The encrypted text)
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* @throws NoSuchPaddingException
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* (from Cipher)
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* @throws NoSuchAlgorithmException
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* (from Cipher)
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* @throws InvalidKeyException
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* (from Cipher)
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* @throws BadPaddingException
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* (from Cipher)
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* @throws IllegalBlockSizeException
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* (from Cipher)
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*/
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public static byte[] encryptText(String plainText, SecretKey secKey) throws NoSuchAlgorithmException,
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NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException {
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// AES defaults to AES/ECB/PKCS5Padding in Java 7
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Cipher aesCipher = Cipher.getInstance("AES");
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aesCipher.init(Cipher.ENCRYPT_MODE, secKey);
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byte[] byteCipherText = aesCipher.doFinal(plainText.getBytes());
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return byteCipherText;
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}
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/**
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* Decrypts encrypted byte array using the key used for encryption.
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*
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* @param byteCipherText
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* @param secKey
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* @return plainText
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* @throws NoSuchPaddingException
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* @throws NoSuchAlgorithmException
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* @throws InvalidKeyException
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* @throws BadPaddingException
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* @throws IllegalBlockSizeException
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*/
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public static String decryptText(byte[] byteCipherText, SecretKey secKey) throws NoSuchAlgorithmException,
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NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException {
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// AES defaults to AES/ECB/PKCS5Padding in Java 7
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Cipher aesCipher = Cipher.getInstance("AES");
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aesCipher.init(Cipher.DECRYPT_MODE, secKey);
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byte[] bytePlainText = aesCipher.doFinal(byteCipherText);
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return new String(bytePlainText);
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}
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/**
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* Convert a binary byte array into readable hex form
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* Old library is deprecated on OpenJdk 11 and
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* this is faster regarding other solution is using StringBuilder
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* Credit
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* {@link
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* https://stackoverflow.com/questions/9655181/how-to-convert-a-byte-array-to-a-hex-string-in-java/9855338#9855338}
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* @param hash
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* (in binary)
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* @return hexHash
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*/
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public static String bytesToHex(byte[] bytes) {
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char[] hexChars = new char[bytes.length * 2];
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for (int j = 0; j < bytes.length; j++) {
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int v = bytes[j] & 0xFF;
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hexChars[j * 2] = HEX_ARRAY[v >>> 4];
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hexChars[j * 2 + 1] = HEX_ARRAY[v & 0x0F];
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}
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return new String(hexChars);
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}
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}
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