// Copyright © 2001 by Neal R. Wagner. All rights reserved.
//   Any use of this code must include a reference to the author.
//
// AESdecrypt: AES decryption
// GetBytes: fetch array of bytes, represented in hex
import java.io.*;
public class GetBytes {
   private String fileName; // input filename
   private int arraySize; // number of bytes to read
   private Reader in;

   // GetBytes: constructor, opens input file
   public GetBytes(String file, int n) {
      fileName = file;
      arraySize = n;
      try {
         in = new FileReader(fileName);
      } catch (IOException e) {
         System.out.println("Exception opening " + fileName);
      }
   }

   // getNextChar: fetches next char
   private char getNextChar() {
      char ch = ' '; // = ' ' to keep compiler happy
      try {
         ch = (char)in.read();
      } catch (IOException e) {
         System.out.println("Exception reading character");
      }
      return ch;
   }

   // val: return int value of hex digit
   private int val(char ch) {
      if (ch >= '0' && ch <= '9') return ch - '0';
      if (ch >= 'a' && ch <= 'f') return ch - 'a' + 10;
      if (ch >= 'A' && ch <= 'F') return ch - 'A' + 10;
      return -1000000;
   }

   // getBytes: fetch array of bytes in hex
   public byte[] getBytes() {
      byte[] ret = new byte[arraySize];
      for (int i = 0; i < arraySize; i++) {
         char ch1 = getNextChar();
         char ch2 = getNextChar();
         ret[i] = (byte)(val(ch1)*16 + val(ch2));
      }
      return ret;
   }
}