Cryptography Algorithm

Transposition Cipher.py

@@ -0,0 +1,43 @@
+import math
+
+def main():
+    message = input('Enter message: ')
+    key = int(input('Enter key [2-%s]: ' % (len(message) - 1)))
+    mode = input('Encryption/Decryption [e/d]: ')
+
+    if mode.lower().startswith('e'):
+        text = encryptMessage(key, message)
+    elif mode.lower().startswith('d'):
+        text = decryptMessage(key, message)
+
+    # Append pipe symbol (vertical bar) to identify spaces at the end.
+    print('Output:\n%s' %(text + '|'))
+
+def encryptMessage(key, message):
+    cipherText = [''] * key
+    for col in range(key):
+        pointer = col
+        while pointer < len(message):
+            cipherText[col] += message[pointer]
+            pointer += key
+    return ''.join(cipherText)
+
+def decryptMessage(key, message):
+    numCols = math.ceil(len(message) / key)
+    numRows = key
+    numShadedBoxes = (numCols * numRows) - len(message)
+    plainText = [""] * numCols
+    col = 0; row = 0;
+
+    for symbol in message:
+        plainText[col] += symbol
+        col += 1
+
+        if (col == numCols) or (col == numCols - 1) and (row >= numRows - numShadedBoxes):
+            col = 0
+            row += 1
+
+    return "".join(plainText)
+
+if __name__ == '__main__':
+    main()