added submission for csmith95

csmith95-assign1/caesar-cipher.txt

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+SBWKRQ

csmith95-assign1/caesar-plain.txt

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+PYTHON

csmith95-assign1/crypto.py

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+"""
+Assignment 1: Cryptography
+Course: CS 92SI
+Name: Conner Smith
+Date: 10/9/15
+
+This program encrypts/decrypts plaintext using either 
+Caesar's cipher, Vigenere's cipher, or railfence cipher
+"""
+import string
+
+LETTERS_IN_ALPHABET = 26
+
+# a dictionary of char-to-char mappings for 
+# Caesar's cipher
+letterMappings = {}
+reverseLetterMappings = {}
+
+# returns character that originalLetter maps to given an offset. Assumes originalLetter
+# is lowercase
+def computeNewLetter(originalLetter, offset):
+    encryptedLetterOffset = (ord(originalLetter) - ord('a') + offset) % LETTERS_IN_ALPHABET
+    # deal with the case of decrypting using vigenere's cipher when letters must wrap around to from 
+    # beginning to end of alphabet
+    if encryptedLetterOffset < 0:
+        return chr(ord('z') + encryptedLetterOffset)
+    return chr(ord('a') + encryptedLetterOffset)
+
+
+# fills dictionaries with letter mappings for caesar's cipher
+def constructLetterMappingsForCaesar():
+    for offset in range(LETTERS_IN_ALPHABET):
+        key = chr(ord('a') + offset)
+        val = computeNewLetter(key, 3)
+        letterMappings[key] = val
+        reverseLetterMappings[val] = key
+
+# encrypts plaintext and returns result in all uppercase
+def encrypt_caesar(plaintext):
+    encrypted = ''
+    for ch in plaintext.lower():
+        encrypted += letterMappings[ch]
+    return encrypted.upper()
+
+# decrypts ciphertext and returns result in all uppercase
+def decrypt_caesar(ciphertext):
+    decrypted = ''
+    for ch in ciphertext.lower():
+        decrypted += reverseLetterMappings[ch]
+    return decrypted.upper()
+
+
+# encrypts plaintext using a Vigenere cipher with a keyword.
+def encrypt_vigenere(plaintext, keyword):
+    encrypted = ''
+    # convert keyword to lowercase string without spaces
+    keyword = keyword.lower().replace(" ", "")
+    for (index, ch) in enumerate(plaintext.lower()):
+        indexInKeyword = index % len(keyword)
+        offset = ord(keyword[indexInKeyword]) - ord('a')
+        encrypted += computeNewLetter(ch, offset)
+    return encrypted.upper()
+
+# decrypts plaintext using a Vigenere cipher with a keyword.
+def decrypt_vigenere(ciphertext, keyword):
+    decrypted = ''
+    # convert keyword to lowercase string without spaces
+    keyword = keyword.lower().replace(" ", "")
+    for (index, ch) in enumerate(ciphertext.lower()):
+        indexInKeyword = index % len(keyword)
+        offset = ord('a') - ord(keyword[indexInKeyword])
+        decrypted += computeNewLetter(ch, offset)
+    return decrypted.upper()
+
+# encrypts plaintext using a railfence cipher.
+def encrypt_railfence(plaintext, num_rails):
+    # handle edge cases
+    if num_rails == 0 or num_rails == 1:
+        return plaintext
+
+    encrypted = ''
+    # construct a list of step_sizes in which the index in the 
+    # list corresponds to the step_size for that row. For the last row, 
+    # step_size should loop around to the 0th index
+    step_sizes = [x for x in range( (2 * num_rails) - 2, 0, -2)]
+    text_length = len(plaintext)
+    for rail_num in range(num_rails):
+        step_size = step_sizes[rail_num % (num_rails - 1)]
+        encrypted += plaintext[rail_num : text_length : step_size]
+    return encrypted.upper()
+
+
+
+""" this doesn't work at all.. I spent way too much time failing. I think all of the
+    other functions work """
+# encrypts plaintext using a railfence cipher.
+def decrypt_railfence(ciphertext, num_rails):
+    # handle edge cases
+    if num_rails == 0 or num_rails == 1:
+        return ciphertext
+
+    text_length = len(ciphertext)
+    # create a list that contains each rail
+    step_sizes = [x for x in range( (2 * num_rails) - 2, 0, -2)]
+    rails = []
+    start = 0
+    for rail_num in range(num_rails):
+        stop = int(text_length / num_rails) + 1 + start
+        rail = ciphertext[start : stop]
+        print(rail)
+        rails.append(rail)
+        start += len(rail)
+
+    rails = ['wecrlte', 'erdsoeefeaoc', 'aivden']
+    print(rails)
+
+
+    decrypted = ''
+    next_index_to_read = [0 for _ in range(num_rails)]
+    curr_rail = 0
+    for x in range(text_length):
+        print(decrypted)
+        print(curr_rail)
+        print(next_index_to_read[curr_rail])
+        index = next_index_to_read[curr_rail]
+        decrypted += rails[curr_rail][index]
+        next_index_to_read[curr_rail] += 1
+        if curr_rail == num_rails - 1:
+            offset = -1
+        elif curr_rail == 0:
+            offset = 1
+        curr_rail = (curr_rail + offset) % num_rails
+
+    return decrypted.upper()
+
+# returns string indicating whether user wants to encrypt, decrypt, or quit
+def promptForTask():
+    task = 'z'
+    while task not in ['e', 'd', 'q']:
+        task = input("Would you like to (e)ncrypt, (d)ecrypt, or (q)uit? ")[0].lower()
+
+    if task == 'e':
+        return 'encrypt'
+    if task == 'd':
+        return 'decrypt'
+    if task == 'q':
+        return 'quit'
+
+# returns string indicating whether user wants to use caesar's, vigenere's, or railfence
+def promptForCipherToUse():
+    choice = 'z'
+    while choice not in ['c', 'v', 'r']:
+        choice = input("Would you like to use (c)aesar's, (v)igenere's, or (r)ailfence? ")[0].lower()
+
+    if choice == 'c':
+        return 'caesar'
+    if choice == 'v':
+        return 'vigenere'
+    if choice == 'r':
+        return 'railfence'
+
+# if user wants to use vigenere's this method returns a string to use as keyword. 
+# if user wants to use railfence, this method returns an int to use as num_rails
+def promptForAdditionalInfo(cipherToUse):
+    if cipherToUse == 'vigenere':
+        return input('Provide a key: ')
+    return int(input('How many rails? '))
+
+# returns text user wants to encrypt or decrypt
+def promptForTextToUse():
+    return input('Enter a string to encrypt/decrypt: ')
+
+# returns copy of text without punctuation characters
+def removePunctuationAndSpace(text):
+    punctuation_set = set(string.punctuation)
+    whitespace_set = set(string.whitespace)
+    text = ''.join(ch for ch in text if ch not in punctuation_set and ch not in whitespace_set)
+    return text.replace(" ", "")
+
+def readingFromFile():
+    response = input("Read from file [Y/N]? ")
+    if response[0].lower() == 'y':
+        return True
+    return False
+
+def writingToFile():
+    response = input("Write to file [Y/N]? ")
+    if response[0].lower() == 'y':
+        return True
+    return False
+
+
+def openFile():
+    filename = input("Enter a filename: ")
+    return open(filename, 'r+')
+
+def performEncryption(originalText, cipherToUse, additional, writeToFile, fw):
+    if cipherToUse == 'caesar':
+            output = encrypt_caesar(originalText)
+    elif cipherToUse == 'vigenere':
+        output = encrypt_vigenere(originalText, additional)
+    else:
+        output = encrypt_railfence(originalText, additional)
+
+    # display result to user
+    if writeToFile:
+        fw.print('Transformed text: ' + output)
+    else:
+        print('Transformed text: ' + output)
+
+def performDecryption(originalText, cipherToUse, additional, writeToFile, fw):
+    if cipherToUse == 'caesar':
+            output = decrypt_caesar(originalText)
+    elif cipherToUse == 'vigenere':
+        output = decrypt_vigenere(originalText, additional)
+    else:
+        output = decrypt_railfence(originalText, additional)
+
+     # display result to user
+    if writeToFile:
+        fw.write('Transformed text: ' + output)
+    else:
+        print('Transformed text: ' + output)
+
+def run_suite():
+    """
+    Runs a single iteration of the cryptography suite.
+
+    Asks the user for input text from a string or file, whether to encrypt
+    or decrypt, what tool to use, and where to show the output.
+    """
+    constructLetterMappingsForCaesar()
+    # obtain task from user
+    task = promptForTask();
+    if task == 'quit':
+        return
+
+    readFromFile = False
+    if readingFromFile():
+        f = openFile()
+        readFromFile = True
+    else:
+        originalText = promptForTextToUse()
+        originalText = removePunctuationAndSpace(originalText)
+
+    writeToFile = False
+    fw = None
+    if writingToFile():
+        fw = openFile()
+        writeToFile = True
+
+
+    # obtain method from user
+    cipherToUse = promptForCipherToUse()
+    additional = 0
+    if cipherToUse != 'caesar':
+        additional = promptForAdditionalInfo(cipherToUse)
+
+    # perform operation
+    if task == 'encrypt':
+        if readFromFile:
+            for line in f:
+                performEncryption(removePunctuationAndSpace(line), cipherToUse, additional, writeToFile, fw)
+        else:
+            performEncryption(originalText, cipherToUse, additional, writeToFile, fw)
+    else: 
+        if readFromFile:
+            for line in f:
+                performDecryption(removePunctuationAndSpace(line), cipherToUse, additional, writeToFile, fw)
+        else:
+            performDecryption(originalText, cipherToUse, additional, writeToFile, fw)
+
+
+# Do not modify code beneath this point.
+def should_continue():
+    """
+    Asks the user whether they would like to continue.
+    Responses that begin with a `Y` return True. (case-insensitively)
+    Responses that begin with a `N` return False. (case-insensitively)
+    All other responses (including '') cause a reprompt.
+    """
+    choice = input("Again (Y/N)? ").upper()
+    while not choice or choice[0] not in ['Y', 'N']:
+        choice = input("Please enter either 'Y' or 'N'. Again (Y/N)? ").upper()
+    return choice[0] == 'Y'
+
+
+def main():
+    """Harness for the Cryptography Suite"""
+    print("Welcome to the Cryptography Suite!")
+    run_suite()
+    while should_continue():
+        run_suite()
+    print("Goodbye!")
+
+
+if __name__ == '__main__':
+    """This block is run if and only if the Python script is invoked from the
+    command line."""
+    main()

csmith95-assign1/feedback.txt

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+Name: Conner Smith
+1) How long did this assignment take you to complete?
+… I didn’t really have time to complete railfence decryption, but I spent about 2 hours on the parts before railfence and 4 hours thinking about railfence.
+
+
+2) What has been the best part of the class so far?
+I like the in-class lab days (the only days 2 days I’ve been in class were lab days). Doing the problems with a partner is more fun.
+
+
+
+
+3) What can we do to make this class more enjoyable for you?
+I’m not sure because I’ve only been to 2 classes, but I like the relaxed feel of the class. It feels very low stress, which is rare for a CS class.
+
+
+
+
+4) What types of assignments would excite you in this class?
+
+I liked this encryption assignment. A web-based assignment would be cool.
+
+
+

csmith95-assign1/railfence-cipher.txt

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+WECRLTEERDSOEEFEAOCAIVDEN

csmith95-assign1/railfence-plain.txt

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+WE ARE DISCOVERED. FLEE AT ONCE

csmith95-assign1/secret_message.txt

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+KHOORZRUOG

csmith95-assign1/vigenere-cipher.txt

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+LXFOPVEFRNHR

csmith95-assign1/vigenere-plain.txt

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+Attack At Dawn!