vigenere cipher in go

vigenere.go

package main

import (
	"flag"
	"fmt"
)

// plaintext flag
var plaintext = flag.String("plaintext", "", "plaintext is the message you want to cipher")

// cipher key flag
var key = flag.String("key", "", "key is the key to use to cipher")

// cipher key flag
var ciphertext = flag.String("ciphertext", "", "ciphertext is the encrypted text")

func main() {
	// parse the commandline flags
	flag.Parse()
	// convert strings from inputs to byte arrays
	var ba_key = []byte(*key)
	var ba_ciphertext = []byte(*ciphertext)
	var ba_plaintext = []byte(*plaintext)

	// validate inputs
	if len(ba_key) < 1 {
		panic("Key must exist")
	}
	// check for valid key chars
	for _, letter := range ba_key {
		// range checking input key
		if letter < 65 || letter > 90 {
			panic(fmt.Sprintf("char '%c' in key is out of range, A-Z only"))
		}
	}
	// this counter will tell us which char of the key to use
	var Ki_count int = 0

	// if we are given plaintext, encrypt
	if len(ba_ciphertext) < 1 && len(ba_plaintext) > 1 {
		// for each of the characters in the plaintext
		for i := 0; i < len(ba_plaintext); i++ {
			// get the Mi (message at i)
			Mi := ba_plaintext[i]
			// get the Ki (key at i)
			Ki := ba_key[Ki_count]
			// range checking input plaintext
			if Mi < 65 || Mi > 90 {
				panic(fmt.Sprintf("char '%c' in plaintext is out of range, A-Z only"))
			}
			// append the ciphertext
			ba_ciphertext = append(ba_ciphertext, ((Mi+Ki)-65<<1)%26+65)
			// if we get beyond the length of ba_key, circle back to start
			if Ki_count++; Ki_count >= len(ba_key) {
				// start at the 0th element again
				Ki_count = 0
			}
		}
		fmt.Println("plaintext: ", string(ba_plaintext))
		fmt.Println("ciphertext: ", string(ba_ciphertext))
	} else if len(ba_ciphertext) > 1 && len(ba_plaintext) < 1 {
		// for each of the characters in the plaintext
		for i := 0; i < len(ba_ciphertext); i++ {
			// get the Mi (message at i)
			Ci := ba_ciphertext[i]
			// get the Ki (key at i)
			Ki := ba_key[Ki_count]
			// range checking input plaintext
			if Ci < 65 || Ci > 90 {
				panic(fmt.Sprintf("char '%c' in ciphertext is out of range, A-Z only"))
			}
			// append the ciphertext
			var CiMinusKi byte = 0
			if Ci < Ki {
				// if Ci - Ki is going to be neg, reverse so we get a positive,
				// and then subtract 26 from that to get the letter position
				CiMinusKi = 26 - (Ki - Ci)
			} else {
				// otherwise, subtract Ci from Ki
				CiMinusKi = Ci - Ki
			}
			ba_plaintext = append(ba_plaintext, CiMinusKi%26+65)
			// if we get beyond the length of ba_key, circle back to start
			if Ki_count++; Ki_count >= len(ba_key) {
				// start at the 0th element again
				Ki_count = 0
			}
		}
		fmt.Println("ciphertext: ", string(ba_ciphertext))
		fmt.Println("plaintext: ", string(ba_plaintext))
	} else {
		fmt.Println("specify either ciphertext or plaintext")
	}
}