Cryptographic Applications - Introduction to Cryptography with Java Applets - page 328

H 0 y 1 ) OR A) 257 F 1 (( ((0000000000000000 1111101111110100) OR

1111000000000000) 100000001 (1111101111110100 OR 1111000000000000) 100000001

1111101111110100 100000001

101011011010010100101011 (mod
10110111001001010111011101).
G 1 is taken to be the 16 rightmost bits of F 1 ; so
G 1 = 1010010100101011.

We take H 1 by computing

H 1 = G 1 H 0 = 1010010100101011.

H 2 in the same way:
F 2 (( H 1 y 2 ) OR A) 257

We compute

((1010010100101011 1010000010100110) OR
1111000000000000) 100000001

(0000010110001101 OR 1111000000000000) 100000001

1111010110001101 100000001

10001000101100100000010111 (mod
10110111001001010111011101).

G 2 = 1100100000010111
H 2 = G 2 H 1 = 1100100000010111 1010010100101011 = 0110110100111100.
The final digest value is 0110110100111100.
Of course, this was a lot to go through for such a tiny message; in fact, in this case, the
digest is larger than the message! Of course, we could have used a message up to 2 8

1 =

255 bits in length for this example.

The MASH2 Class I have designed a class to generate digests of messages using the
MASH-2 algorithm. The digestOf() method accepts a message as a byte array, and returns
the digest as a byte array.

import java.math.*;
import java.security.*;
public class MASH2 {

//Define some handy values
static BigInteger two=BigInteger.valueOf(2);
static BigInteger ten=BigInteger.valueOf(10);//=binary 1010
static BigInteger fifteen=BigInteger.valueOf(15);//=binary 1111
static BigInteger sixteen=BigInteger.valueOf(16);
static BigInteger exp=BigInteger.valueOf(257);

BigInteger modulus;

public MASH2(BigInteger modulus) {
this.modulus=modulus;

}