crypto-spring-2019-e2q2.go

package main

import (
	"encoding/hex"
)

func main() {
	cipherTextHex := "09e1c5f70a65ac519458e7e53f36"
	plaintext := "attack at dawn"
	newPlainText := "attack at dusk"

	p := []byte(plaintext)
	c, _ := hex.DecodeString(cipherTextHex)
	key := crack(p, c)

	p2 := []byte(newPlainText)
	c2 := enc(p2, key)
	println(hex.EncodeToString(c2))
}

func enc(plaintext []byte, key []byte) []byte {
	cipherText := xorBytes([]byte(plaintext), key)
	return cipherText
}

func crack(plaintext []byte, cipherText []byte) []byte {
	key := xorBytes(plaintext, cipherText)
	return key
}

func xorBytes(b1 []byte, b2 []byte) []byte {
	r := make([]byte, len(b1))
	for i := 0; i < len(b1); i++ {
		r[i] = b1[i] ^ b2[i]
	}
	return r
}