added submission for keyur

keyur-assign1/crypto.py

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+"""
+Assignment 1: Cryptography
+Course: CS 92SI
+Name: Keyur Mehta
+Date: 10/7/2015
+
+Replace this with a description of the program.
+"""
+import math
+
+def encrypt_caesar(plaintext):
+    """
+    Encrypts plaintext using a Caesar cipher.
+    Creates a dictionary that maps the letters to their Caesar equivalent. 
+    Uses that dictionary to make ciphertext
+    """
+
+    alpha_str = "abcdefghijklmnopqrstuvwxyz"
+    caesar_for_map = {letter:alpha_str[(index+3)%26] for index, letter in enumerate(alpha_str)}
+
+    ptext = plaintext.lower()
+    new_text = ''
+
+    for letter in ptext:
+        new_text = new_text + caesar_for_map.get(letter)
+
+    return new_text
+
+
+def decrypt_caesar(ciphertext):
+    """
+    Decrypts a ciphertext using a Caesar cipher.
+    Creates a Caesar to plain dictionary by reversing the previously made one. 
+    Uses this dictionary to create the plaintext. 
+    """
+    alpha_str = "abcdefghijklmnopqrstuvwxyz"
+    caesar_for_map = {letter:alpha_str[(index+3)%26] for index, letter in enumerate(alpha_str)}
+    caesar_rev_map = {value:key for key, value in caesar_for_map.items()}
+
+    ctext = ciphertext.lower()
+    new_text = ''
+
+    for letter in ctext:
+        new_text = new_text + caesar_rev_map.get(letter)
+
+    return new_text
+
+
+def encrypt_vigenere(plaintext, keyword):
+    """
+    Encrypts plaintext using a Vigenere cipher with a keyword.
+    Gets the proper key by extending it if its too small and then selecting the letters to match the plaintext length.
+    Uses the ord and chr functions to convert letters to their number equivelent add them and then convert back to letters. 
+    """
+    p_text = plaintext.upper()
+    kw_extend = (keyword*(math.ceil(len(p_text)/len(keyword))))[:len(p_text)].upper()
+
+    new_word = ''
+    for index, letter in enumerate(p_text):
+        new_word = new_word + chr(65+((ord(letter) + ord(kw_extend[index]) - 65*2) % 26))
+
+    return new_word
+
+
+def decrypt_vigenere(ciphertext, keyword):
+    """
+    Decrypts ciphertext using a Vigenere cipher with a keyword.
+    Gets the proper key by extending it if its too small and then selecting the letters to match the ciphertext length.
+    Uses the ord and chr functions to convert letters to their number equivelent subtract the keyword from the cipher to get the plain
+    """
+    c_text = ciphertext.upper()
+    kw_extend = (keyword*(math.ceil(len(c_text)/len(keyword))))[:len(c_text)].upper()
+
+    new_word = ''
+    for index, letter in enumerate(c_text):
+        new_word = new_word + chr(65+((ord(letter) - ord(kw_extend[index]) - 65*2) % 26))
+
+    return new_word
+
+#ERROR CHECKING WITH SHORT STRINGS
+def encrypt_railfence(plaintext, num_rails):
+    """
+    Encrypts plaintext using a railfence cipher.
+    Determines the increment depending on the number of rails. Then creates a word to add
+    based on if its on the ends or in the middle, using the increment.
+    """
+    p_text = plaintext.upper()
+    new_word = ''
+
+    if num_rails == 1:
+        increment = 1
+    else:
+        increment = num_rails*2 - 2
+
+    for i in range(num_rails):
+        if i == 0 or i == num_rails-1:
+            new_word = new_word + p_text[i::increment]
+        else:
+            new_seg_1 = p_text[i::increment]
+            start = 2*(num_rails - 1) - i
+            new_seg_2 = p_text[start::increment]
+
+            # word_add = ''*(len(new_seg_1) + len(new_seg_2))
+            # word_add[::2] = p_text[i::increment]
+            # word_add[1::2] = p_text[start::increment]
+
+            word_add = ''
+            for ind, let in enumerate(new_seg_1):
+                if len(new_seg_1) != len(new_seg_2) and ind == len(new_seg_2):
+                    word_add = word_add + let
+                else:
+                    word_add = word_add + let + new_seg_2[ind]
+
+            new_word = new_word + word_add
+    return new_word
+
+
+def decrypt_railfence(ciphertext, num_rails):
+    """
+    Encrypts plaintext using a railfence cipher.
+    Creates a new vector that stores the actual indices of all the letters in the ciphertext.
+    Uses these indices to rearrange the letters in the ciphertext order. 
+    """
+    c_text = ciphertext.upper()
+    new_word_list = ['']*len(c_text)
+
+    if num_rails == 1:
+        increment = 1
+    else:
+        increment = num_rails*2 - 2
+
+    ind_list = []
+
+    for i in range(num_rails):
+        if i == 0 or i == num_rails-1:
+            new_nums = range(i, len(c_text), increment)
+        else:
+            new_seg_1 = range(i, len(c_text), increment)
+            start = 2*(num_rails - 1) - i
+            new_seg_2 = range(start, len(c_text), increment)
+
+            new_nums = []
+            for ind, num in enumerate(new_seg_1):
+                if len(new_seg_1) != len(new_seg_2) and ind == len(new_seg_2):
+                    new_nums.append(num)
+                else:
+                    new_nums.append(num)
+                    new_nums.append(new_seg_2[ind])
+
+        for n in new_nums:
+            ind_list.append(n)
+
+    for ind,num in enumerate(ind_list):
+        new_word_list[num] = c_text[ind];
+
+    new_str = ''.join(new_word_list)
+    return new_str
+
+
+def read_from_file(filename):
+    """
+    Reads and returns content from a file.
+    Uses with for error catching.
+    """
+    with open(filename) as f:
+        content = f.readlines()
+    return content[0]
+
+
+def write_to_file(filename, content):
+    """
+    Writes content to a file.
+    Uses with for error checking. 
+    """
+
+    with open(filename, "wt") as f:
+        f.write(content)
+
+def mod_string(old_str):
+    """
+    Removes all of the non-letters from the string. 
+    """
+    new_str = ''
+    for letter in old_str:
+        if letter.isalpha():
+            new_str = new_str + letter
+    new_str = new_str.upper()
+    return new_str
+
+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.
+    """
+    print("*Input*")
+
+    to_read = ''
+    filename = ''
+    while(True):
+        inp = input("(F)ile or (S)tring? ").lower()
+        if inp == 'f':
+            filename = input("Filename: ")
+            to_read = mod_string(read_from_file(filename))
+            break
+        elif inp == 's':
+            to_read = mod_string(input("Enter the string to encrypt: "))
+            break
+
+    print("*Transform*")
+
+    en_or_de = ''
+    while(True):
+        en_or_de = input("(E)ncrypt or (D)ecrypt? ").lower()
+        if en_or_de == 'e' or en_or_de == 'd':
+            break
+
+    cryp_type = ''
+    while(True):
+        cryp_type = input("(C)aesar, (V)igenere, or (R)ailfence? ").lower()
+        if(cryp_type == 'c' or cryp_type == 'v' or cryp_type == 'r'):
+            break
+
+    type_print = ''
+    if en_or_de == 'e':
+        gen_type = "Encrypting"
+        if cryp_type == 'c':
+            crpy_out = encrypt_caesar(to_read)
+            type_print = "Caesar"
+            extra = ""
+        elif cryp_type == 'v':
+            passkey = mod_string(input("Passkey? "))
+            crpy_out = encrypt_vigenere(to_read, passkey)
+            type_print = "Vigenere"
+            extra = "with key " + passkey 
+        else:
+            num_rails = int(input("Number of rails? "))
+            crpy_out = encrypt_railfence(to_read, num_rails)
+            type_print = "Railfence"
+            extra = "with " + str(num_rails) + " rails."
+    else:
+        gen_type = "Decrypting"
+
+        if cryp_type == 'c':
+            crpy_out = decrypt_caesar(to_read)
+            type_print = "Caesar"
+            extra = ""
+        elif cryp_type == 'v':
+            passkey = input("Passkey? ")
+            crpy_out = decrypt_vigenere(to_read, passkey)
+            type_print = "Vigenere"
+            extra = "with key " + passkey
+        else:
+            num_rails = int(input("Number of rails? "))
+            crpy_out = decrypt_railfence(to_read, num_rails)
+            type_print = "Railfence"
+            extra = "with " + str(num_rails) + " rails."
+
+    if inp == 'f':
+        print(gen_type, "contents of", filename, "using", type_print, "cipher", extra)
+    else:
+        print(gen_type, to_read, "using", type_print, "cipher", extra)
+
+    print("*Output*")
+
+    while(True):
+        out_type = input("(F)ile or (S)tring? ")
+        type_out = "plaintext"
+        if en_or_de == 'e':
+            type_out = "ciphertext"
+        if out_type == 'f':
+            out_file = input("Filename: ")
+            to_read = write_to_file(out_file, crpy_out)
+            print("Writing ", type_out, " to ", out_file)
+            break
+        elif out_type == 's':
+            print("The ", type_out, "is: ", crpy_out)
+            break
+
+# 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()

keyur-assign1/feedback.txt

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+Name: <Keyur Mehta>
+1) How long did this assignment take you to complete?
+
+Around 5 and a half hours. Majority of the time on the railfence algorithm!
+
+
+2) What has been the best part of the class so far?
+
+Loved the pace so far and think Sam is teaching incredibly relevant material.
+
+3) What can we do to make this class more enjoyable for you?
+
+It would be great to get "real world applications" stuff from the class as well. We could talk 
+about what Python is used for in the real world (as in personal projects, apps, websites...etc.) And
+then in lab, we could go over a real example. 
+
+4) What types of assignments would excite you in this class?
+
+Similar to my previous answer, I'd love a real world assignment where we are scraping data from the web or
+writing scripts that automate something useful!
+
+Thank you guys so much for all the work you've been putting into the class. Its already been one of my 
+most enjoyable academic experiences and its only been 3 weeks. Thought this assignment went a long way in 
+confirming basic control of Python which was perfect. Thanks again. 
+
+
+
+
+