Merge pull request #647 from photon149/master

Caesar Cipher using Python

Author: smv1999

Cryptography/Caesar_Cipher.py

@@ -0,0 +1,84 @@
+'''
+Aim: Given a string S , encrypt or decrypt it as per the choice entered by the user using Caesar Cipeher Substitution Method
+    
+Input Format: 
+1. The first line provides an option to the user to choose either to encrypt/decrypt
+2. In the second line the user inputs the string as per his choice given in part 1.
+
+Note : It is considered that the encrypted string consists of both upper and lowercase letters , while the decrypted strings consist of only uppercase letters.
+'''
+
+def decrypt(encrypted_string,key_val):
+    '''This is the decryption function
+    It takes in input encrypted string and key value
+    Prints nothing and return the decrypted string value'''
+    final = ""
+    encrypted_string = encrypted_string.upper()
+    for i in range(len(encrypted_string)):
+        decrypt_char = ord(encrypted_string[i]) + key_val
+        if (decrypt_char > 90):
+            decrypt_char = 65 - ( 90 - decrypt_char)
+        decrypt_char = chr(decrypt_char)
+        decrypt_char = decrypt_char.lower()
+        final += decrypt_char
+    return final
+
+
+def encrypt(input_string,key_val):
+    '''This is the encryption function
+    It takes in input string and key value.
+    Prints nothing and return the Encrypted string value'''
+    final = ""
+    input_string = input_string.upper()
+    for i in range(len(input_string)):
+        encrypt_char = ord(input_string[i]) + key_val
+        if (encrypt_char > 90):
+            encrypt_char = 65 - ( 90 - encrypt_char)
+        encrypt_char = chr(encrypt_char)
+        encrypt_char = encrypt_char.lower()
+        final += encrypt_char
+    return final
+
+#DRIVER CODE
+
+#This is the code for menu , chosing whether to encrypt or decrypt
+choose =int(input('CHOOSE FROM THE FOLLOWING : \n 1. Encrypt String \n 2. Decrypt String \n')) 
+
+#This is the code for encryption choice , it calls the function and prints the  encrypted value
+if (choose == 1):
+    input_string = input('Enter the input text ')
+    key_val = int(input('Enter the key value '))
+    print('Encrypted string is : ' + encrypt(input_string,key_val))
+    
+#This is the code for decryption choice , it calls the function and prints the decrypted value
+if (choose == 2):
+    encrypted_string = input('Enter the encrypted text ')
+    key_val = int(input('Enter the key value '))
+    print('Decrypted string is : ' + decrypt(encrypted_string,key_val))
+
+ '''
+ Sample Test Case :
+ Case 1 :
+        User chooses to input string and encrypt the inputted string.
+            input :  
+                string : escrsce
+                key value  : 5
+            output :
+                encrypted string : JXHxwhJ
+                
+ Case 2 :
+        User chooses to enter an encrypted string and decrypt it.
+            input :
+                string : trWEcere
+                key value : 6
+            output :
+                Decrypted String : ZXDKIKXK
+                
+ Explaination :
+    In this program , we take the input string and key value .Once we get the key value , we substitute the alphabet of the string with the updated key value alphabet.
+    For eg . if input character is A and key value is 3 , so it will be subsituted by D ( A + 3 = D)
+    Also in case if the encrypted string consists of both lower and uppercase characters we convert the whole string to uppercase
+    
+ '''
+
+