already written java code for encryption and decryption

[Adedeji Adedoyin]

Am thinking if I could get an already written java code that can encrypt and at d same time decrypt...instead of me having to go learn how to use java's cryptography technology..

[Stanley Mungai]

Welcome to the Ranch,
I have a ready code that encrypt and decrypt Strings and I would really like to help. But that is not the Practice here. Try a code, if it does not work , let us know what the problem is and we will surely help. We only need to see that you tried. Otherwise, Ready Made codes are just a wrong way to learn Java.....and we really want you to learn.

[Adedeji Adedoyin]

Thanks a lot sir...that sounds like the best idea..learn rather than rely on ready-made codes...

Please I would be so grateful if you could tell me how to start with java cryptography tutorials..probably you could recommend a good book that I can start with or video tutorials..thanks alot

[Stanley Mungai]

http://www.ibm.com/developerworks/java/tutorials/j-sec1/
for the basics, Or you can read the E-book at
http://www.digitallibrary.kcci.com.pk/bitstream/32417747/138/1/%28ebook-pdf%29%20-%20O%27Reilly%20Java%20Cryptography.pdf

Try and try and try and never be afraid to try. If you get an issue, You will find a lot of guys here ready to help.
I hope this helps.

[Maneesh Godbole]

Adedeji Adedoyin wrote:...if you could tell me how to start with java cryptography tutorials..

Recommended reading http://java.sun.com/developer/technicalArticles/Security/AES/AES_v1.html

[Stanley Mungai]

Probably an easy User Interactive Example to start you off you would be;

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package encrypt.string;

/**
 *
 * @author Stano
 */
public class EncryptString {


    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
  try {
      // quick way to do input from the keyboard, now deprecated...
      java.io.StreamTokenizer Input=new java.io.StreamTokenizer(System.in);
      //
      System.out.print("Input your secret password : ");
      Input.nextToken();
      String hash = byteArrayToHexString(EncryptString.computeHash(Input.sval));
      System.out.println("the computed hash (hex string) : " + hash);
      boolean ok = true;
      String inputHash = "";
      while (ok) {
          System.out.print("Now try to enter a password : " );
          Input.nextToken();
          inputHash = byteArrayToHexString(EncryptString.computeHash(Input.sval));
          if (hash.equals(inputHash)){
             System.out.println("You got it!");
             ok = false;
             }
          else
             System.out.println("Wrong, try again...!");
      }
    }
    catch (Exception e){
      e.printStackTrace();
    }
  }

  public static byte[] computeHash(String x)   
  throws Exception  
  {
     java.security.MessageDigest d =null;
     d = java.security.MessageDigest.getInstance("SHA-1");
     d.reset();
     d.update(x.getBytes());
     return  d.digest();
  }
  
  public static String byteArrayToHexString(byte[] b){
     StringBuffer sb = new StringBuffer(b.length * 2);
     for (int i = 0; i < b.length; i++){
       int v = b[i] & 0xff;
       if (v < 16) {
         sb.append('0');
       }
       sb.append(Integer.toHexString(v));
     }
     return sb.toString().toUpperCase();       
     
    }
}

[Stanley Mungai]

I hope I did Not give the Proverbial beggar A Fish.

[Tim Moores]

It should be noted that a hash is generally not considered an encryption, since hashing can't be reversed.

[Adedeji Adedoyin]

Thank you very much to everyone that has contributed to dis thread....I am very grateful...am a first_timer right here in coderanch....and am so glad am beginning to get solutions. To problems as regards to java programming....I still will welcome many more comments on dis topic...

[Tim Moores]

Start with the articles Stanley and Maneesh posted; those should get you going.

[Adedeji Adedoyin]

Thanks a lot to all those that responded earlier...I have started with the tutorial on IBM's website...and I have 2 questions to ask

1)I discoverd that different digests were created for two strings containing d same words..example

String plaintext="americanvisa";

String plaintext="americanvisa";

Produced different digest output(using toString())..why is this so?..I thought the same digest shud be generated for strings containing d same words...

2)Now..given the fact that equal strings produce different digests..then how do we really compare to knw if a data was tampered with or not...

[Adedeji Adedoyin]

Jus want to correct a mistake...the variable name for the second string should be "plaintext2" not "plaintext"..

[Joanne Neal]

Please note the following words do not exists in English d, shud, dis
At least not in the context you are using them.

[Adedeji Adedoyin]

I am sorry for the mis-use of words by the use of abbreviations...henceforth,I will take note of this...thank you

[Joe Ess]

2)Now..given the fact that equal strings produce different digests..then how do we really compare to knw if a data was tampered with or not...

Can you show us the code you are using? My wild guess is that you are not "resetting" the digest before getting the second result, in effect comparing the digest of "americanvisa" with "americanvisaamericanvisa".

[Nishanth Thomas]

/* AES alogrithm using password key */
   /* developed by Nishanth Thomas */


   import java.security.spec.AlgorithmParameterSpec;
    import javax.crypto.Cipher;
    import javax.crypto.spec.IvParameterSpec;
    import javax.crypto.spec.SecretKeySpec;
    import sun.misc.BASE64Encoder;

    /*  Mode = CipherMode.CBC,-( Cipher-block chaining)
        Padding = PaddingMode.PKCS7 or PKCS5,
        KeySize = 128,
        BlockSize = 128,
        Key = keyBytes - password,
        IV = keyBytes  - password*/

  public class testencrypt {


  Cipher cipher; 
  // Input encrypted String
  static  String input = "Hi This is my String";
  // password for encryption
  final static String strPassword = "password12345678";
  // put this as key in AES
  static SecretKeySpec key = new SecretKeySpec(strPassword.getBytes(), "AES");

  public static void main(String args []) throws Exception{

     // Parameter specific algorithm
    AlgorithmParameterSpec paramSpec = new     IvParameterSpec(strPassword.getBytes()); 
    //Whatever you want to encrypt/decrypt
    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

    // You can use ENCRYPT_MODE (ENCRYPTunderscoreMODE)  or DECRYPT_MODE (DECRYPT underscore MODE) 
    cipher.init(Cipher.ENCRYPT_MODE, key, paramSpec); 

    // encrypt data 
     byte[] ecrypted = cipher.doFinal(input.getBytes());

     // encode data using standard encoder
     String output =  new BASE64Encoder().encode(ecrypted);

     System.out.println("Orginal tring: " + input);
     System.out.println("Encripted string: " + output);

      }

 }


/// Decryption 





/* Decrypt using AES with password */

   /* developed by Nishanth Thomas */

  import java.security.spec.AlgorithmParameterSpec;
  import javax.crypto.Cipher;
  import javax.crypto.spec.IvParameterSpec;
  import javax.crypto.spec.SecretKeySpec;
  import sun.misc.BASE64Decoder;

    public class testDecrypt {

  /*  Mode = CipherMode.CBC,-( Cipher-block chaining)
    Padding = PaddingMode.PKCS7 or PKCS5,
    KeySize = 128,
    BlockSize = 128,
    Key = keyBytes,
    IV = keyBytes */

     Cipher cipher; 

    // Input encrypted String
    static  String input = "sw0SrUIKe0DmS7sRd9+XMgtYg+BUiAfiOsdMw/Lo2RA=";

   // password to decrypt 16 bit
    final static String strPassword = "password12345678";

   // put this as key in AES
   static SecretKeySpec key = new SecretKeySpec(strPassword.getBytes(), "AES");


   public static void main(String args []) throws Exception{

    AlgorithmParameterSpec paramSpec = new IvParameterSpec(strPassword.getBytes()); 
    //Whatever you want to encrypt/decrypt using AES /CBC padding
    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

    //You can use ENCRYPT_MODE or DECRYPT_MODE 
     cipher.init(Cipher.DECRYPT_MODE, key, paramSpec);  

     //decode data using standard decoder
     byte[] output =  new BASE64Decoder().decodeBuffer(input);  

       // Decrypt the data 
     byte[] decrypted = cipher.doFinal(output);

     System.out.println("Original string: " +
             new String(input));

     // decryptedData .;
     System.out.println("Decrypted string: " +
     new String(decrypted));    

   }

 }