CLWW16 toy project

clww16.go

package main

import (
	"crypto/hmac"
	"crypto/sha256"
	"fmt"
)

func main() {
	fmt.Println("Example CLWW 2016 Implementation")

	var (
		M uint16 = 3

		// input, what we are encrypting
		m1 byte = 44
		m2 byte = 42
		// output, what we can compare
		u1 uint16
		u2 uint16

		// temp calculation binary
		b1 byte
		b2 byte
	)

	// Encrypt
	// for each bit in our inputs
	for i := 7; i >= 0; i-- {
		// our PRF is hmac sha256
		mac1 := hmac.New(sha256.New, []byte("secretkey"))
		mac2 := hmac.New(sha256.New, []byte("secretkey"))

		// shift to the right location
		b1 = m1 >> byte(i)
		b2 = m2 >> byte(i)

		// do our prf
		mac1.Write([]byte{b1 << byte(i)})
		tmp1 := mac1.Sum(nil)[0]
		u1 = (u1 << 1) | (uint16(tmp1)+uint16((b1&1)))%M

		mac2.Write([]byte{b2 << byte(i)})
		tmp2 := mac2.Sum(nil)[0]
		u2 = (u2 << 1) | (uint16(tmp2)+uint16((b2&1)))%M
	}
	fmt.Printf("u1: %b\n", u1)
	fmt.Printf("u2: %b\n", u2)

	var equal bool = true
	// compare
	for i := 7; i >= 0; i-- {
		// find the first bit that doesn't match
		uu1 := u1 >> uint8(i) & 1
		uu2 := u2 >> uint8(i) & 1
		if uu1 != uu2 {
			if (uu1+1)%M == uu2 {
				equal = false
				fmt.Println("m1 is less than m2")
				break
			}
			fmt.Println("m2 is less than m1")
			break
		}
	}
	if equal {
		fmt.Println("m1 is equal to m2")
	}
}