Merge pull request #16 from Namyalg/Substitution-Cipher

Substitution cipher

Author: yashaswibiyahut

Substitution_Cipher/README.md

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+## Substitution Cipher
+
+- The Substitution Cipher is a Cryptographic technique used for the encryption of a message
+- The encryption is done based on a key agreed upon by the sender and receiver of the message
+- The letter is encoded/mapped to a different letter/character
+
+## Working
+
+- The user is prompted to enter the message as well as the key according to which the message will be encrypted
+- The key will be accepted as a CSV file
+- Considering an example : 
+
+![Image](assets/key.PNG)
+
+- This is the key as agreed upon both the parties
+- On running the script, the user is prompted to enter a message
+
+![Image](assets/encrypt.PNG)

Substitution_Cipher/assets/encrypt.PNG

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+a,w
+b,e
+c,2
+d,q
+t,z
+y,4
+m,s
+f,1
+o,l

Substitution_Cipher/assets/key.PNG

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+#This script implements Substitution Cipher
+#The key for encrypting the message must be passed as a Command line argument in the form of a csv file
+
+#To run the script from terminal, run
+#python3 substitution_cipher.py "path_to_csv_file_containing_the_key"
+
+import csv
+import sys
+
+def get_key():
+    key = dict()
+    with open(sys.argv[1] , 'r') as file:
+        reader = csv.reader(file)
+        for row in reader:
+            key[str(row[0])] = str(row[1])
+    return(key)
+
+def encrypt():
+    key = get_key()
+    message = input("Enter the message ")
+    encrypted_message = ''
+    for letter in message:
+        try:
+            encrypted_message += key[letter]
+        except:
+            alert = "Your key does not have a suitable match for " + letter +  "\nPlease update your key and try again!" 
+            return(-1, alert)
+    return(0, encrypted_message)
+
+if __name__ == "__main__":
+    exit_code, message = encrypt()
+    if (exit_code == 0):
+        print("The encrypted message is " , message)
+    else:
+        print(message)