package chapter3;import java.security.Key;import java.security.MessageDigest;import java.security.SecureRandom;import javax.crypto.Cipher;import javax.crypto.spec.IvParameterSpec;/** * Tampered message, encryption with digest, AES in CTR mode */public class TamperedDigestExample{       public static void main(        String[]    args)        throws Exception    {        SecureRandom	random = new SecureRandom();        IvParameterSpec ivSpec = Utils.createCtrIvForAES(1, random);        Key             key = Utils.createKeyForAES(256, random);        Cipher          cipher = Cipher.getInstance("AES/CTR/NoPadding", "BC");        String          input = "Transfer 0000100 to AC 1234-5678";        MessageDigest   hash = MessageDigest.getInstance("SHA1", "BC");                System.out.println("input : " + input);                // encryption step                cipher.init(Cipher.ENCRYPT_MODE, key, ivSpec);                byte[] cipherText = new byte[cipher.getOutputSize(input.length() + hash.getDigestLength())];        int ctLength = cipher.update(Utils.toByteArray(input), 0, input.length(), cipherText, 0);                hash.update(Utils.toByteArray(input));                ctLength += cipher.doFinal(hash.digest(), 0, hash.getDigestLength(), cipherText, ctLength);                // tampering step                cipherText[9] ^= '0' ^ '9';                // replace digest                byte[] originalHash = hash.digest(Utils.toByteArray(input));        byte[] tamperedHash = hash.digest(Utils.toByteArray("Transfer 9000100 to AC 1234-5678"));                for (int i = ctLength - hash.getDigestLength(), j = 0; i != ctLength; i++, j++)        {            cipherText[i] ^= originalHash[j] ^ tamperedHash[j];        }                // decryption step                cipher.init(Cipher.DECRYPT_MODE, key, ivSpec);                byte[] plainText = cipher.doFinal(cipherText, 0, ctLength);        int    messageLength = plainText.length - hash.getDigestLength();                hash.update(plainText, 0, messageLength);                byte[] messageHash = new byte[hash.getDigestLength()];        System.arraycopy(plainText, messageLength, messageHash, 0, messageHash.length);                System.out.println("plain : " + Utils.toString(plainText, messageLength) + " verified: " + MessageDigest.isEqual(hash.digest(), messageHash));    }}