diff --git a/ciphers/AESEncryption.java b/ciphers/AESEncryption.java new file mode 100644 index 00000000..7ecb0874 --- /dev/null +++ b/ciphers/AESEncryption.java @@ -0,0 +1,83 @@ +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); + } +}