diff --git a/vigenere.js b/vigenere.js
new file mode 100644
index 0000000000..3a2be958f7
--- /dev/null
+++ b/vigenere.js
@@ -0,0 +1,91 @@
+/**
+ * Cleans the input text by removing spaces and ensuring it contains only alphanumeric characters.
+ * @param {string} text - The input text to be cleaned.
+ * @returns {string} The cleaned text without spaces or special characters.
+ * @throws Will throw an error if special characters are found.
+ */
+function cleanText(text) {
+    const textNoSpaces = text.replace(/ /g, "");
+    if (/[^A-Za-z0-9]/.test(textNoSpaces)) {
+        throw new Error("Special characters detected. They must be removed.");
+    }
+    return textNoSpaces;
+}
+
+/**
+ * Encrypts a message using a key with a substitution cipher.
+ * @param {string} message - The message to encrypt.
+ * @param {string} key - The encryption key.
+ * @returns {string} The encrypted message.
+ */
+function encrypt(message, key) {
+    message = message.toLowerCase();
+    key = key.toLowerCase();
+    const combinedAlphabet = "abcdefghijklmnopqrstuvwxyz0123456789";
+    const n = combinedAlphabet.length;
+    const encrypted = [];
+    let keyIndex = 0;
+
+    for (const char of message) {
+        if (combinedAlphabet.includes(char)) {
+            const mIndex = combinedAlphabet.indexOf(char);
+            const keyChar = key[keyIndex % key.length];
+            const shift = combinedAlphabet.indexOf(keyChar);
+            const newIndex = (mIndex + shift) % n;
+            encrypted.push(combinedAlphabet[newIndex]);
+            keyIndex++;
+        }
+    }
+    return encrypted.join("");
+}
+
+/**
+ * Decrypts an encrypted message using a key with a substitution cipher.
+ * @param {string} cipherText - The encrypted message to decrypt.
+ * @param {string} key - The decryption key.
+ * @returns {string} The decrypted message.
+ */
+function decrypt(cipherText, key) {
+    cipherText = cipherText.toLowerCase();
+    key = key.toLowerCase();
+    const combinedAlphabet = "abcdefghijklmnopqrstuvwxyz0123456789";
+    const n = combinedAlphabet.length;
+    const decrypted = [];
+    let keyIndex = 0;
+
+    for (const char of cipherText) {
+        if (combinedAlphabet.includes(char)) {
+            const cIndex = combinedAlphabet.indexOf(char);
+            const keyChar = key[keyIndex % key.length];
+            const shift = combinedAlphabet.indexOf(keyChar);
+            const originalIndex = (cIndex - shift + n) % n;
+            decrypted.push(combinedAlphabet[originalIndex]);
+            keyIndex++;
+        }
+    }
+    return decrypted.join("");
+}
+
+/**
+ * The main function to clean, encrypt, and decrypt messages.
+ */
+function main() {
+    try {
+        const rawMessage = prompt("Enter the message: ");
+        const rawKey = prompt("Enter the key: ");
+        const cleanedMessage = cleanText(rawMessage);
+        const cleanedKey = cleanText(rawKey);
+        
+        if (!cleanedMessage) throw new Error("Message is empty after cleaning!");
+        if (!cleanedKey) throw new Error("Key is empty after cleaning!");
+
+        const encryptedMsg = encrypt(cleanedMessage, cleanedKey);
+        alert(`Encrypted Message: ${encryptedMsg}`);
+        const decryptedMsg = decrypt(encryptedMsg, cleanedKey);
+        alert(`Decrypted Message: ${decryptedMsg}`);
+    } catch (e) {
+        alert(`An error occurred: ${e.message}`);
+    }
+}
+
+main();