feat: add caesar cipher implementation

ciphers/caesar_cipher.ts

@@ -0,0 +1,35 @@
+/**
+ * @function CaesarCipherEncrypt
+ * @description - Encrypt using the Caesar Cipher
+ * The Caesar Cipher is a kind of a substitution cipher.
+ * Each character is shifted by a constant value that is defined as the key.
+ * @param {string} str - string to be encrypted
+ * @param {number} key - key value for encryption
+ * @return {string} encrypted string
+ */
+export const CaesarCipherEncrypt = (str: string, key: number): string => {
+  // We normalize the Shift value here to make sure that the key value always falls in the range of 0 to 25
+  const normalizedShift: number = ((key % 26) + 26) % 26;
+
+  return str.replace(/[a-z]/gi, (char: string) => {
+    const base = char <= "Z" ? 65 : 97;
+    return String.fromCharCode((char.charCodeAt(0) - base + normalizedShift) % 26 + base);
+  })
+}
+
+/**
+ * @function CaesarCipherDecrypt
+ * @description - Decrypt using the Caesar Cipher
+ * Each character is shifted back by a constant value that is defined as the key.
+ * @param {string} str - string to be decrypted
+ * @param {number} key - key value used for encryption
+ * @return {string} decrypted string
+ */
+export const CaesarCipherDecrypt = (str: string, key: number): string => {
+  const normalizedShift: number = ((key % 26) + 26) % 26;
+
+  return str.replace(/[a-z]/gi, (char: string) => {
+    const base = char <= "Z" ? 65 : 97;
+    return String.fromCharCode((char.charCodeAt(0) - base - normalizedShift) % 26 + base);
+  })
+}