Need help with encryption

I understand one way encryption, but let's have a situation.

I have two programs. One will write to a .db file. The second one will read the .db file. (both are separate programs ran by different people).

The writing will done using Strings indicated from a text field (unique values), meaning that the reading must be done completely off the data.db file, the reading program will have no source for the values except for the data.db file.

How can I encrypt the values into the data.db using the writer, and then read their true value using the reader? (keeping in mind that it can't be easily decrypted by an outside source)

Thanks a lot,
~Solarsonic888

 

I would think PGP encryption should be good enough to meet those needs. Have fun figuring out something like an "easy" library from Gnu though.

 

You can use public key encryption and just store the secret key internally in the reader.

 

You could also use symmetric encryption for encrypting the strings.

Code:

import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import java.security.Key;
import java.security.InvalidKeyException;
import javax.crypto.spec.SecretKeySpec;

public class Cryptograph {

    private Cipher cipher;
    private Key key;
    //create user key.
    private byte[] keyBytes = new byte[16];
    private byte[] jceKeyBytes = new byte[32];

    //default 256 bit key.
    /*
    private static byte[] defaultKeyBytes = new byte[] {
    (byte) 0x00a, (byte) 0x01b, (byte) 0x02c, (byte) 0x03dd, //32 bit
    (byte) 0x04e, (byte) 0x05f, (byte) 0x0a1, (byte) 0x0c2, //64 bit
    (byte) 0x0d3, (byte) 0x0e4, (byte) 0x0f5, (byte) 0x100, //96 bit
    (byte) 0x00e, (byte) 0x00d, (byte) 0x00e, (byte) 0x00f, //128 bit
    (byte) 0x00a, (byte) 0x00b, (byte) 0x00d, (byte) 0x0f6, //160 bit
    (byte) 0x0f7, (byte) 0x0f9, (byte) 0x000, (byte) 0x001, //192 bit
    (byte) 0x002, (byte) 0x003, (byte) 0x004, (byte) 0x005, //224 bit
    (byte) 0x006, (byte) 0x007, (byte) 0x008, (byte) 0x009  //256 bit
    };
     */

    public Cryptograph() {


    };

    private void generateKey(String input, boolean jcePolicy) {

        if (jcePolicy == true) {

            for (int i = 0; i < input.length(); i++) {

                jceKeyBytes[i] = (byte) input.charAt(i);
            }
            key = new SecretKeySpec(jceKeyBytes, "AES");
        }
        else {
            
            for (int i = 0; i < input.length(); i++) {

                keyBytes[i] = (byte) input.charAt(i);
            }
            key = new SecretKeySpec(keyBytes, "AES");
        }
    }

    public byte[] encrypt(String input, String inputKey, boolean jcePolicy) throws InvalidKeyException,
            BadPaddingException,
            IllegalBlockSizeException,
            NoSuchAlgorithmException,
            NoSuchPaddingException,
            NoSuchProviderException {

        generateKey(inputKey, jcePolicy);

        cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, key);

        byte[] inputBytes = input.getBytes();

        return cipher.doFinal(inputBytes);
    }

    public String decrypt(byte[] input, String inputKey, boolean jcePolicy) throws InvalidKeyException,
            BadPaddingException,
            IllegalBlockSizeException,
            NoSuchAlgorithmException,
            NoSuchPaddingException {

        generateKey(inputKey, jcePolicy);

        cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE, key);

        byte[] decryptedBytes = cipher.doFinal(input);

        return new String(decryptedBytes);
    }
}

Code:

public class HexadecimalEncoder {


    public HexadecimalEncoder() {

    }

     //convert byte to hex-encoded string
    public String byteToHexString(byte bytes[]) {

        StringBuffer retString = new StringBuffer();

        for (int i = 0; i < bytes.length; ++i) {

            retString.append(Integer.toHexString(0x0100 + (bytes[i] & 0x00FF)).substring(1));
        }
        return retString.toString();
    }

    //convert hex-encoded string to byte
    public byte[] hexStringToByte(String s) {

        byte[] bts = new byte[s.length() / 2];

        for (int i = 0; i < bts.length; i++) {

            bts[i] = (byte) Integer.parseInt(s.substring(2 * i, 2 * i + 2), 16);
        }
        return bts;
    }

    //convert string to hex-encoded string
    public String stringToHex(String s) {

        char[] chars = s.toCharArray();
        StringBuffer output = new StringBuffer();

        for (int i = 0; i < chars.length; i++) {

            output.append(Integer.toHexString((int) chars[i]));
        }
        return output.toString();
    }
    //convert hex-encoded string to string

    public String hexToString(String s) {

        byte[] txtInByte = new byte[s.length() / 2];
        int j = 0;
        for (int i = 0; i < s.length(); i += 2) {
            txtInByte[j++] = Byte.parseByte(s.substring(i, i + 2), 16);
        }
        return new String(txtInByte);
    }

}