XOR encryption and decryption

xor-encryption-decryption.js

/**
 * Convert character string to binary
 *
 * @param {String} str Character string
 * @returns Binary String
 */
function toBinary(str) {
    let binary = '';
    for (let i = 0, l = str.length; i < l; i++) {
        binary += str.codePointAt(i).toString(2).padStart(8, '0');
    }
    return binary;
}

console.assert(
    toBinary('a') === '01100001'
);
console.assert(
    toBinary('abc') === '011000010110001001100011'
);

/**
 * Convert binary string to character string
 *
 * @param {String} binary Binary String
 * @returns Character String
 */
function toText(binary){
    let str = '';
    for (let i = 0, l = binary.length / 8; i < l; i++) {
        const start = i * 8;
        const byte = binary.slice(start, start + 8);
        const codePoint = parseInt(byte, 2);
        str += String.fromCodePoint(codePoint);
    }
    return str;
}

console.assert(
    toText('01100001') === 'a'
);
console.assert(
    toText('011000010110001001100011') === 'abc'
);

/**
 * Perform exclusive OR operation
 *
 * @param {Number|String} a
 * @param {Number|String} b
 * @returns {Number} 0 or 1
 */
function xor(a, b) {
    return +(a !== b);
}

console.assert(
    xor(1, 0) === 1
);
console.assert(
    xor(0, 1) === 1
);
console.assert(
    xor(1, 1) === 0
);
console.assert(
    xor(0, 0) === 0
);


/**
 * Perform XOR operations on two strings
 *
 * @param {String} key Key to XOR
 * @param {String} text Text to XOR
 * @returns {String} XOR'd string
 */
function xorStrings(key, text){
    const keyBin = toBinary(key);
    const keyLength = keyBin.length;
    const textBin = toBinary(text);
    const textLength = textBin.length;

    let xorText = '';

    for (let i = 0; i < textLength; i++) {
        const ctElement = textBin[i];
        const keyElement = keyBin[i % keyLength];

        xorText += xor(ctElement, keyElement).toString();
    }

    return xorText;
}

console.assert(
    xorStrings('a', 'b') === '00000011'
);
console.assert(
    xorStrings('b', 'a') === '00000011'
);
console.assert(
    xorStrings('abc', 'cba') === '000000100000000000000010'
);


/**
 * Encrypt text using key
 *
 * @param {String} key
 * @param {String} clearText
 * @returns {String} Encrypted text
 */
function encrypt(key, clearText){
    return toText( xorStrings( key, clearText ) );
}

console.assert(
    encrypt('a', 'bc') === ''
);

/**
 * Decrypt encrypted text using key
 *
 * @param {String} key
 * @param {String} cipherText
 * @returns {String} Decrypted text
 */
function decrypt(key, cipherText) {
    return toText( xorStrings(key, cipherText) );
}

console.assert(
    decrypt( 'key', encrypt( 'key', 'abc' ) ) === 'abc'
);
console.assert(
    decrypt('whatever', encrypt('whatever', 'what is this sentence huh')) === 'what is this sentence huh'
);
console.assert(
    decrypt('abc', encrypt('abc', 'cba')) === 'cba'
);
console.assert(
    decrypt('wrong-key', encrypt('whatever', 'I should not work')) !== 'I should not work'
);