Encrypt plain text using vignere cipher.

vignere_cipher.py

@@ -0,0 +1,56 @@
+# create a dictionary of the alphabets according to their corresponding numbers
+alpha_dict = {
+    "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,
+}
+
+try:
+    # Input the key text
+    key = input("Enter key text: ").lower()
+
+    # Input the plain text
+    plain_text = input("Enter plain text: ").lower()
+
+    if len(key) > len(plain_text):
+        raise Exception("Key length is greater than plain text length")
+
+    # Initialise the cipher text
+    cipher_text = ""
+
+    # Convert the plain text to cipher text
+    for i in range(len(plain_text)):
+        if plain_text[i].isalpha():
+            cipher_text += chr(
+                ((alpha_dict.get(plain_text[i]) + alpha_dict.get(key[i % len(key)])) % 26) + 97)
+        else:
+            cipher_text += plain_text[i]
+
+    # Print the cipher text
+    print("Cipher text: ", cipher_text)
+
+except:
+    print("Please enter a valid key text, length smaller than that of plain text!!")