add decrypt and update encrypt

src/vigenere/vig.py

@@ -1,13 +1,16 @@
 def encrypt(key, plaintext):
-    pln_bytes = bytes(plaintext, 'UTF-8')
-    key_bytes = bytes(key, 'UTF-8')
     out=""
+    for i in range(0, len(plaintext)):
+        out = out + chr(((ord(key[i%len(key)])+ord(plaintext[i])-(0x61+0x61))%26)+0x61)
+    return out
 
-    for i in range(len(pln_bytes)):
-        pln_chr_index = pln_bytes[i] - 0x61
-        key_chr_index = key_bytes[i % len(key)] - 0x61
-        out_chr_index = (pln_chr_index + key_chr_index) % 26
-        out = out + chr(out_chr_index + 0x61)
+def decrypt(key, cipertext):
+    out=""
+    for i in range(0, len(cipertext)):
+        pln = ord(cipertext[i])-(ord(key[i%len(key)]) - 0x61)
+        if pln < 0x61:
+            pln = pln + 26
+        out = out + chr(pln)
     return out
 
 if __name__ == "__main__":
@@ -20,5 +23,15 @@ if __name__ == "__main__":
     parser.add_argument('--out', metavar='FILE')
 
     args = parser.parse_args()
+    fd = open(args.FILE, "r")
+    txt_in = fd.read()
+    txt = ""
+    for i in txt_in.lower():
+        if i.isalpha():
+            txt = txt + i
+
+    if(args.encrypt != None):
+        print(encrypt(args.encrypt, txt))
 
-print(encrypt("bbb", "test"))
+    if(args.decrypt != None):
+        print(decrypt(args.decrypt, txt))