One time pad, encryption and decryption

Question

I am trying to pick up cryptography and had been trying this exercise

Write a program (preferably Java) to generate a one-time pad, which is a relatively large file

Answer 1

First here is a OTP algorithm specified called HOTP which is a standard RFC. Almost all other OTP are propriety and we don't know the algorithm for those.

http://tools.ietf.org/html/rfc4226

There is some java code in there you can use to learn how its done. Second if you are going to do encryption don't use Random. Random is nice for psuedo random, but if you really want a good source of random data you need to adopt SecureRandom. That's a much better source of random numbers that are suitable for cryto algorithms.

For converting things to Hex you can easily use

http://docs.oracle.com/javase/1.5.0/docs/api/java/math/BigInteger.html#toString(int)

Or any of the varieties Long.toString(value,radix), Integer.toString(value,radix), or Byte.toString(value,radix).

byte[] bytes = ...;
for( int i = 0; i < bytes.length; i++ ) {
    System.out.println( Integer.toString( bytes[i], 16 );
}