Caesar Cipher

bin/caesar_cipher.py

@@ -0,0 +1,42 @@
+key = 'abcdefghijklmnopqrstuvwxyz'
+
+def encrypt(n, plaintext):
+    """Encrypt the string and return the ciphertext"""
+    result = ''
+
+    for l in plaintext.lower():
+        try:
+            i = (key.index(l) + n) % 26
+            result += key[i]
+        except ValueError:
+            result += l
+
+    return result.lower()
+
+
+def decrypt(n, ciphertext):
+    """Decrypt the string and return the plaintext"""
+    result = ''
+
+    for l in ciphertext:
+        try:
+            i = (key.index(l) - n) % 26
+            result += key[i]
+        except ValueError:
+            result += l
+
+    return result
+
+print("Encrypt or decrypt?")
+ans = input()
+ans = ans.lower()
+print("Enter message")
+k = input()
+print("Enter rotation number")
+nn = int(input())
+if ans == 'encrypt':
+    ret = encrypt(nn,k)
+    print ('Encrytped: %s' % ret)
+else:
+    ret = decrypt(nn,k)
+    print ('Decrytped: %s' % ret)