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Author: Salinimahapatra

Python/Caeser Cipher Algorithm.py

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+'''
+The encryption step performed by a Caesar cipher is often incorporated as part of more complex schemes, such as the Vigenère cipher, and still has modern application in the ROT13 system. As with all single-alphabet substitution ciphers, the Caesar cipher is easily broken and in modern practice offers essentially no communications security.
+
+The action of a Caesar cipher is to replace each plaintext letter with a different one a fixed number of places down the alphabet.
+
+The encryption can also be represented using modular arithmetic by first transforming the letters into numbers, according to the scheme, A → 0, B → 1, ..., Z → 25.[2] Encryption of a letter x by a shift n can be described mathematically as,
+
+Encryption(x) = (x + n)%26
+Decryption(x) = (x - n)%26
+'''
+
+'''
+Algorithm for Caesar Cipher: 
+
+Input: A String of lower case letters, called Text and an Integer between 0-25 denoting the required shift.
+
+Procedure: 
+1. Traverse the string characters.
+2. For each character, transform the given character as per the rule, depending on whether we’re encrypting or decrypting the text.
+3. Return the new string generated.
+
+To decrypt remember Cipher(n) = De-cipher(26-n)
+'''
+
+def encrypt(plain_text, n):
+    result = ""
+
+    for i in range(len(plain_text)):
+        char = plain_text[i]
+ 
+        # Encrypt uppercase characters
+        if (char.isupper()):
+            result += chr((ord(char) + n-65) % 26 + 65)
+ 
+        # Encrypt lowercase characters
+        else:
+            result += chr((ord(char) + n - 97) % 26 + 97)
+ 
+    return result
+
+def decrypt(encrypted_string, n):
+    result = ""
+    n = 26 - n
+
+    for i in range(len(encrypted_string)):
+        char = encrypted_string[i]
+ 
+        # Encrypt uppercase characters
+        if (char.isupper()):
+            result += chr((ord(char) + n-65) % 26 + 65)
+ 
+        # Encrypt lowercase characters
+        else:
+            result += chr((ord(char) + n - 97) % 26 + 97)
+ 
+    return result
+
+plain_text = "TestThisString"
+n = 4
+print("Text  : ", plain_text)
+print("Shift : ", str(n))
+encrypted_string = encrypt(plain_text, n)
+print("Cipher: ", encrypt(plain_text, n))
+print("Decrypted Cipher Text: ", decrypt(encrypted_string, n))