/** * Check if the Character is letter or not * @param {String} character - character to check * @return {object} An array with the character or null if isn't a letter */ function isLetter(str) { return str.length === 1 && str.match(/[a-zA-Z]/i); } /** * Check if is Uppercase or Lowercase * @param {String} character - character to check * @return {Boolean} result of the checking */ function isUpperCase(character){ if (character == character.toUpperCase()) { return true; } if (character == character.toLowerCase()){ return false; } } /** * Encrypt a Vigenere cipher * @param {String} message - string to be encrypted * @param {String} key - key for encrypt * @return {String} result - encrypted string */ function encrypt(message, key) { let result = ""; for (let i = 0, j = 0; i < message.length; i++) { let c = message.charAt(i); if (isLetter(c)){ if(isUpperCase(c)) { result += String.fromCharCode((c.charCodeAt(0) + key.toUpperCase().charCodeAt(j) - 2 * 65) % 26 + 65); // A: 65 } else { result += String.fromCharCode((c.charCodeAt(0) + key.toLowerCase().charCodeAt(j) - 2 * 97) % 26 + 97); // a: 97 } } else { result+=c; } j = ++j % key.length; } return result; } /** * Decrypt a Vigenere cipher * @param {String} message - string to be decrypted * @param {String} key - key for decrypt * @return {String} result - decrypted string */ function decrypt(message, key) { let result =""; for(let i = 0, j = 0; i < message.length; i++){ let c = message.charAt(i); if (isLetter(c)){ if(isUpperCase(c)) { result += String.fromCharCode(90-(25-(c.charCodeAt(0)-key.toUpperCase().charCodeAt(j)))%26); } else { result += String.fromCharCode(122-(25-(c.charCodeAt(0)-key.toLowerCase().charCodeAt(j)))%26); } } else { result+=c; } j = ++j % key.length; } return result; } let messageEncrypt = encrypt('Hello World!', 'code'); console.log(messageEncrypt); // "Jhpnr Yrvng!" let messageDecrypt = decrypt('Jsopq Zstzg!', 'code'); console.log(messageDecrypt); // "Hello World!"