symmetrical-encryption.js

const alphabet = {
	"a": 0,
	"b": 1,
	"c": 2,
	"d": 3,
	"e": 4,
	"f": 5,
	"g": 6,
	"h": 7,
	"i": 8,
	"j": 9,
	"k": 10,
	"l": 11,
	"m": 12,
	"n": 13,
	"o": 14,
	"p": 15,
	"q": 16,
	"r": 17,
	"s": 18,
	"t": 19,
	"u": 20,
	"v": 21,
	"w": 22,
	"x": 23,
	"y": 24,
	"z": 25,
	" ": 26,
	 0: "a",
	 1: "b",
	 2: "c",
	 3: "d",
	 4: "e",
	 5: "f",
	 6: "g",
	 7: "h",
	 8: "i",
	 9: "j",
	10: "k",
	11: "l",
	12: "m",
	13: "n",
	14: "o",
	15: "p",
	16: "q",
	17: "r",
	18: "s",
	19: "t",
	20: "u",
	21: "v",
	22: "w",
	23: "x",
	24: "y",
	25: "z", 
	26: " "
}

const encrypt = (data, key) => {
	data = data.replace(/[.,\/#!$%\^&\*;:{}=\-_`~()']/g,"").toLowerCase()
	// split data into array, change letters to numbers, add key
	const numbers = data.split("").map( char => alphabet[char] + key)
	// take number % the length of the alphabet, map back to letters and return
	const letters = []
	numbers.forEach( num => {
		letters.push(alphabet[num % 27])

	})
	return letters.join("")
}

const decrypt = (data, key) => {
	// split data into array, change letters to numbers, add the length of the alphabet minus the key modulo the length of the alphabet
	const numbers = data.split("").map( char => alphabet[char] + (27 - key % 27))
	// take number modulus 26 (length of alphabet), map back to letters and return
	const letters = []
	numbers.forEach( num => {
		letters.push(alphabet[num % 27])

	})
	return letters.join("")
}

let a = encrypt("hello", 69834902303)
console.log(a)
console.log(decrypt(a, 69834902303))

let b = encrypt("If I do one thing right, god bless it'll be flipping this pancake proper.", 932849023843029)
console.log(b)
console.log(decrypt(b, 932849023843029))