CODEWITHSUNDEEP
javaencryption
nikhil k
nikhil k

Reputation: 1

when i am decrypting ,i am not getting the proper plaintext

  import java.security.Key;
    import java.security.MessageDigest;
    import java.security.NoSuchAlgorithmException;
    import java.security.SecureRandom;
    import java.security.Security;
    import java.util.Arrays;
    import javax.crypto.Cipher;
    import javax.crypto.KeyGenerator;
    import javax.crypto.SecretKey;
    import javax.crypto.spec.IvParameterSpec;
    import javax.crypto.spec.SecretKeySpec;
    import java.security.MessageDigest;

 public class SHAhashingexample 
    {
        public static void main(String[] args)throws Exception
        {
            Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
            String usernametohash = "123456";
            String salt="salty food";
            String userdata="hello how are you!";
            MessageDigest md = MessageDigest.getInstance("SHA-256");
            md.update((usernametohash+salt).getBytes());
            byte byteData[] = md.digest();
            System.out.println("Digested value : " + byteData);
            StringBuffer sb = new StringBuffer();
            for (int i = 0; i < byteData.length; i++) 
            {
             sb.append(Integer.toString((byteData[i] & 0xff) + 0x100, 16).substring(1));
            }
             System.out.println("Hash code value of username : " + sb);
               byte[] actualkey=sb.toString().getBytes();
             byte[] first_key = Arrays.copyOf(actualkey, 16);
            Key key = new SecretKeySpec(first_key, "AES");
            System.out.println("Derived AES key is "+key.toString());
            SecureRandom random = new SecureRandom();
            IvParameterSpec ivSpec = createCtrIvForAES(1, random);
            Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding", "BC");
            cipher.init(Cipher.ENCRYPT_MODE, key, ivSpec);
            byte[] cipherText = cipher.doFinal(userdata.getBytes()); 
            System.out.println("ciphertext is : " + cipherText);
            cipher.init(Cipher.DECRYPT_MODE, key, ivSpec);
            byte[] plainText = cipher.doFinal(cipherText)  ; 
            System.out.println("plaintext is : " + plainText);

          }

        public static IvParameterSpec createCtrIvForAES(int messageNumber, SecureRandom random)
        {
            byte[] ivBytes = new byte[16];
            random.nextBytes(ivBytes);
           for (int i = 0; i < 16; i++)
           {
              ivBytes[i] = 0;
            }
          return new IvParameterSpec(ivBytes);
          }
    }

My intention is to derive aes 128 bit key from username hash and hardcoded random number taking algorithms SHA-256 and AES CTR mode.wanted to generate username hash by using SHA-256 algorithm.i felt we require IV to use with CTR mode and what should be the values for Initialization vector i just guessed to be all zero'es...

Upvotes: 0

Views: 189

Answers (1)

Maarten Bodewes
Maarten Bodewes

Reputation: 93968

You are doing many things wrong here, but your actual problem is that you forget to recreate a String from the returned value using new String(plainText).

Everything up to and including the key derivation is not well either. Try and find some Java samples using PBKDF2 (there should be plenty on this site) and try and understand (character-) encoding in Java as well.

Upvotes: 1

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