HW3

py

School

Georgia Institute Of Technology *

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Course

6040

Subject

Computer Science

Date

Feb 20, 2024

Type

py

Pages

3

Uploaded by ChancellorSteelSeaUrchin34

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#!/usr/bin/env python # coding: utf-8 # # Using Python for Research Homework: Week 3, Case Study 1 # # A cipher is a secret code for a language. In this case study, we will explore a cipher that is reported by contemporary Greek historians to have been used by Julius Caesar to send secret messages to generals during times of war. # ### Exercise 1 # # A cipher is a secret code for a language. In this case study, we will explore a cipher that is reported by contemporary Greek historians to have been used by Julius Caesar to send secret messages to generals during times of war. # # The Caesar cipher shifts each letter of a message to another letter in the alphabet located a fixed distance from the original letter. If our encryption key were `1`, we would shift `h` to the next letter `i`, `i` to the next letter `j`, and so on. If we reach the end of the alphabet, which for us is the space character, we simply loop back to `a`. To decode the message, we make a similar shift, except we move the same number of steps backwards in the alphabet. # # Over the next five exercises, we will create our own Caesar cipher, as well as a message decoder for this cipher. In this exercise, we will define the alphabet used in the cipher. # # #### Instructions # - The `string` library has been imported. Create a string called `alphabet` consisting of the space character `' '` followed by (concatenated with) the lowercase letters. Note that we're only using the lowercase letters in this exercise. # In[3]: import string alphabet = ' ' + string.ascii_lowercase # ### Exercise 2 # # In this exercise, we will define a dictionary that specifies the index of each character in `alphabet`. # # #### Instructions # - `alphabet` has already defined in the last exercise. Create a dictionary with keys consisting of the characters in alphabet and values consisting of the numbers from 0 to 26. # - Store this as `positions`. # In[14]: positions = {} for i in range(len(alphabet)): positions[alphabet[i]] = i
positions['n'] # ### Exercise 3 # # In this exercise, we will encode a message with a Caesar cipher. # # #### Instructions # # - `alphabet` and `positions` have already been defined in previous exercises. Use `positions` to create an encoded message based on message where each character in message has been shifted forward by 1 position, as defined by positions. # - **Note that you can ensure the result remains within 0-26 using result % 27** # - Store this as `encoded_message`. # In[22]: message = "hi my name is caesar" def encode(message): encoded_message = '' for i in message: for k,v in positions.items(): if v == (positions[i] + 1) %27: encoded_message += k return encoded_message encode("hi my name is caesar") # ### Exercise 4 # # In this exercise, we will define a function that encodes a message with any given encryption key. # # #### Instructions # - `alphabet`, `position` and `message` remain defined from previous exercises. Define a function `encoding` that takes a message as input as well as an int encryption key `key` to encode a message with the Caesar cipher by shifting each letter in message by key positions. # - Your function should return a string consisting of these encoded letters. # - Use `encoding` to encode message using `key = 3` and save the result as `encoded_message`. # Print `encoded_message`. # In[25]: def encoding(message, key): result = '' for i in message: for k,v in positions.items(): if v == (positions[i] + key) %27: result += k return result encoded_message = encoding("hi my name is caesar", 3) print(encoded_message)
# ### Exercise 5 # # In this exercise, we will decode an encoded message. # # #### Instructions # - Use `encoding` to decode `encoded_message`. # - Store your encoded message as `decoded_message`. # - Print `decoded_message`. Does this recover your original message? # In[26]: # In[28]: decoded_message = encoding(encoded_message, -3) print(decoded_message) # In[ ]:
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