Issue #67: Added new encryption algorithm

joseph-alan-jose · joseph-alan-jose · commit 187233f79a5a · 2023-03-27T15:17:40.000+05:30
diff --git a/algorithms/cryptography/columnar_transposition_cipher.py b/algorithms/cryptography/columnar_transposition_cipher.py
@@ -0,0 +1,54 @@
+import math
+def encrypt(key, message):
+    ciphertext = [] 
+    for col in range(key):
+        position = col
+        while position < len(message):
+            ciphertext.append(message[position])
+            position += key
+    return ''.join(ciphertext)
+
+def decrypt(key, message):
+    numOfRows = math.ceil(len(message) / key)
+    plaintext = []
+    cipher = [*message]
+    remainder = len(message)%key
+    count=0
+    if(remainder != 0):
+        for i in range(0,len(message),numOfRows):
+            count += 1
+            if(count > remainder):
+                cipher.insert(i+numOfRows-1,'#')
+        cipher.append('#')
+        for row in range(numOfRows):
+            position = row
+            while(position < len(cipher)):
+                plaintext.append(cipher[position])
+                position += numOfRows
+        plaintext = [ele for ele in plaintext if ele != '#']
+    else:
+        for row in range(numOfRows):
+            position = row
+            while(position < len(message)):
+                plaintext.append(message[position])
+                position += numOfRows
+    return ''.join(plaintext)
+def main():
+    while(True):
+        print("1. Encrypt")
+        print("2. Decrypt")
+        print("3. Exit")
+        option = int(input("Enter the option: "))
+        if(option == 1):
+            text = input("Enter the plain text: ")
+            k = int(input("Enter the key: "))
+            cipher = encrypt(k,text)
+            print("Ciphertext: ", cipher)
+        if(option == 2):
+            text = input("Enter the ciphertext: ")
+            k = int(input("Enter the key: "))
+            plain = decrypt(k, text)
+            print("Plaintext: ", plain)
+        if(option == 3):
+            break
+main()
