RSAExampleUtils

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;

public class Utils
{
    private static String   digits = "0123456789abcdef";

    public static byte[] toByteArray( String string )
   {
       byte[]   bytes = new byte[string.length()];
       char[]  chars = string.toCharArray();

       for (int i = 0; i != chars.length; i++)
       {    bytes[i] = (byte)chars[i];
       }
       return bytes;
   }

  public static String toHex( byte[] data )
  { return toHex(data, data.length);
  }

   public static String toHex(byte[] data, int length)
   {
       StringBuffer buf = new StringBuffer();
       for (int i = 0; i != length; i++)
       {
           int  v = data[i] & 0xff;
           buf.append(digits.charAt(v >> 4));
           buf.append(digits.charAt(v & 0xf));
       }
       return buf.toString();
   }


    private static class FixedRand extends SecureRandom
    {
        MessageDigest   sha;
        byte[]          state;

        FixedRand()
        {
            try
            {
                this.sha = MessageDigest.getInstance("SHA-1");
                this.state = sha.digest();
            }
            catch (NoSuchAlgorithmException e)
            {
                throw new RuntimeException("can't find SHA-1!");
            }
        }

        public void nextBytes( byte[] bytes)
        {
            int off = 0;

            sha.update(state);

            while (off < bytes.length)
            {
                state = sha.digest();

                if (bytes.length - off > state.length)
                {
                    System.arraycopy(state, 0, bytes, off, state.length);
                }
                else
                {
                    System.arraycopy(state, 0, bytes, off, bytes.length - off);
                }

                off += state.length;

                sha.update(state);
            }
        }
    }

    /**
     * Return a SecureRandom which produces the same value.
     * <b>This is for testing only!</b>
     * @return a fixed random
     */
    public static SecureRandom createFixedRandom()
    {
        return new FixedRand();
    }
}