Ceaser Cipher

Author: Blooverh

PythonDataStructsAndAlgo/Array_Based_Seqs/CeaserCipher.py

@@ -0,0 +1,52 @@
+class CeaserCipher:
+    """Class for doing encryption and decryption of ceaser cipher criptography"""
+    
+    def __init__(self, shift):
+        """Construct Ceaser Cipher using the given integer shight for rotation"""
+        """shift parameter holds the value for the shifting of the character in the list for the
+        encryption"""
+        #temp array for encryption
+        encoder=[None] * 26 #creates a list containing 26 indices with value None
+
+        #temp array for decryption
+        decoder=[None] * 26 #creates a list containing 26 indices with value None
+
+        for k in range(26):
+            encoder[k]= chr((k+shift) % 26 + ord('A')) #reamainder of index k + value of shift + Unicode integer value of letter A
+            # example: 0+3 % 26 + 65 = 3+65 =68 -> which is letter D so we shift letter A 3 places to the left going to the end of the list
+
+            decoder[k]=chr((k-shift) % 26 + ord('A')) #remainder index k - shift value + the UNICODE value of A (65)
+            # example: 3-6 % 26 + 65= -3 +65 = 62 
+
+        self._forward=''.join(encoder) # creates a string object from the list encoder
+        self._backward=''.join(decoder) # creates a string object from the list decoder 
+
+    def encrypt(self, message):
+        """Function that takes the String message object and applies the function forward to shift the elements of the encoder list"""
+        """Returns the string representation of the encrypted message"""
+        return self._transform(message, self._forward)
+    
+    def decrypt(self, secret):
+        """Returns the String of the secret which is the encrypted message"""
+        return self._transform(secret, self._backward)
+
+    def _transform(self, original, code):
+        """Function to perform transformation based on given code string"""
+        msg=list(original) #msg becomes a list of the string object orginal containing on each index a character from string object original 
+
+        """for k in length of the list message that takes original message and encrypts and takes secret message and decrypts"""
+        for k in range(len(msg)):
+            if msg[k].isupper(): # if letter at msg[k] is an Upper case letter
+                j= ord(msg[k]) - ord('A') # object j will hold the value of the UNICODE integer of the character at msg[k] minus UNICODE of A which is 65
+                msg[k]= code[j] # We then assign to msg[k] the character that is at position j in the list code which is based on the encoder or decoder list from previous functions
+                #giving us the list containing the secret message or the original message
+        return ''.join(msg) #returns the list msg in a string object
+    
+if __name__ == '__main__':
+    cipher=CeaserCipher(3)
+    message= "DIOGO"
+    coded=cipher.encrypt(message)
+    print('Secret: ', coded)
+
+    answer= cipher.decrypt(coded)
+    print('Message: ', answer)

PythonDataStructsAndAlgo/Notes.md

@@ -144,4 +144,19 @@
     for k from 1 to n-1 do
         Insert A[k] at its proper location within A[0], A[1],..., A[k]
 
-### Simple cryptography 
+### Using Characters as Array Indices
+
+> Example A=0, B=1 etc.. So When writing a Ceaser Cipher Algorithm, we apply the rotation of r as a simple formula. Replace each letter i with the letter (i+r) mode 26 which returns the remainder after performing an integer division.
+
+> In Python characters are represented in UNICODE by integer code points, and the code points for the uppercase letters are consecutive, thus for simplicity we restrict the encryption to used only uppercase letters.
+
+> Function to retrive the UNICODE Integer value in python is *ord(c)* which takes a parameter character c and returns the integer value associated with it.
+
+>Function to retrive a one character string from a UNICODE integer is *chr(j)* where j is an integer value that will return the one character string.
+
+### Multi dimensional data sets
+
+> 2-D arrays can be also called matrices.
+
+> *A common representation for a 2-D list in Python is a list of lists*
+>> Example: data=[[22,18,709,5,33], [45,32,830,120,750], [4,880,45,66,61]] which is a matrix of 3 x 4 3 rows, and 4 columns