add caesar and encryption funcs

index.py

@@ -0,0 +1,36 @@
+import argparse
+
+
+def caesar(ptextletter, keyletter):
+    ptextNum = ord(ptextletter) - ord('A')
+    keyletterNum = ord(keyletter) - ord('A')
+    return chr((ptextNum + keyletterNum) % 26 + ord('A'))
+
+
+def encryption(plaintext, key):
+    ciphertext = ''
+    for i in range(len(plaintext)):
+        ciphertext += caesar(plaintext[i], key[i % len(key)])
+    return ciphertext
+
+
+def decryption(ciphertext, key):
+    return ciphertext
+
+
+def main():
+    # parse command line argument
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--ptext', type=str)
+    parser.add_argument('--key', type=str)
+    args = parser.parse_args()
+
+    key = args.key
+    ciphertext = encryption(args.ptext, key)
+
+    print("Ciphertext: " + ciphertext)
+    print("Decrypted plaintext: " + decryption(ciphertext, key))
+
+
+if __name__ == '__main__':
+    main()