added submission for alandeng

alandeng-assign1/crypto.py

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+"""
+Assignment 1: Cryptography
+Course: CS 92SI
+Name: Alan Deng
+Date: Oct 9, 2015
+
+Cryptography suite implementing the Caesar, Vigenere, and Railfence ciphers
+to encrypt or decrypt user supplied input strings from a file or the terminal,
+along with secondary parameters specific to each method. User also specifies
+whether the output is written to file or displayed on terminal.
+"""
+
+def encrypt_caesar(plaintext, shift):
+    """
+    Encrypts plaintext using a Caesar cipher with a default shift of 3.
+    User can override with alternative value to shift, taken mod 26. 
+    Assumes input plaintext consists of capitalized alphabetical string.
+    If shifted index goes beyond 'Z', wraps back around to the beginning
+    """
+    shift = shift % 26
+    output = [chr(ord(letter) + shift) for letter in plaintext]
+    for i in range(len(output)):
+        if ord(output[i]) > ord("Z"): #index out of range
+            output[i] = chr(ord(output[i]) - 26)
+    return "".join(output)
+
+def decrypt_caesar(ciphertext, shift):
+    """
+    Decrypts ciphertext using a Caesar cipher with a default shift of 3.
+    User can override with alternative value to shift, taken mod 26. 
+    Assumes input ciphertext consists of capitalized alphabetical string.
+    If shifted index goes below 'A', wraps back around to the end
+    """
+    shift = shift % 26
+    output = [chr(ord(letter) - shift) for letter in ciphertext]
+    for i in range(len(output)):
+        if ord(output[i]) < ord("A"): #index out of range
+            output[i] = chr(ord(output[i]) + 26)
+    return "".join(output)
+
+def encrypt_vigenere(plaintext, keyword):
+    """
+    Encrypts plaintext using a Vigenere cipher with a keyword.
+    Assumes plaintext and keyword are both capitalized alphabetical strings.
+    If shifted index goes beyond 'Z', wraps back around to the beginning
+    """
+    keyphrase = keyword * (len(plaintext) // len(keyword) + 1) #repeat keyword
+    output = [chr(ord(x) + ord(y) - 65) for (x,y) in zip(plaintext, keyphrase)] #cap letters start at 64
+    for i in range(len(output)):
+        if ord(output[i]) > ord("Z"): #index out of range
+            output[i] = chr(ord(output[i]) - 26)
+    return "".join(output)
+
+def decrypt_vigenere(ciphertext, keyword):
+    """
+    Decrypts ciphertext using a Vigenere cipher with a keyword.
+    Assumes ciphertext and keyword are both capitalized alphabetical strings.
+    If shifted index goes below 'A', wraps back around to the end
+    """
+    keyphrase = keyword * (len(ciphertext) // len(keyword) + 1) #repeat keyword
+    output = [chr(ord(x) - ord(y) + 65) for (x,y) in zip(ciphertext, keyphrase)]
+    for i in range(len(output)):
+        if ord(output[i]) < ord("A"): #index out of range
+            output[i] = chr(ord(output[i]) + 26)
+    return "".join(output)
+
+def encrypt_railfence(plaintext, num_rails):
+    """
+    Encrypts plaintext using a railfence cipher with a given number of rails.
+    The first and last rails only have elements spaced evenly apart.
+    The other rails in between have a secondary component going back up, 
+    which is alternately spliced with this rail to generate the complete rail. 
+    If the number of rails is 1, the plaintext is returned as the ciphertext.
+    """
+    if num_rails == 1:
+        return(plaintext)
+    output = []
+    for i in range(num_rails):
+        down_rail = plaintext[i::2*(num_rails - 1)]
+        if (i in range (1, num_rails - 1)):
+            up_rail = plaintext[(2*(num_rails-1)-i)::2*(num_rails - 1)]
+            output_string = ["".join(x) for x in zip(down_rail, up_rail)]
+            if len(down_rail) > len(up_rail):
+                output_string.append(down_rail[-1])
+            output.append("".join(output_string))
+        else:
+            output.append(down_rail)
+    return "".join(output)
+
+def decrypt_railfence(ciphertext, num_rails):
+    """
+    Decrypts ciphertext using a railfence cipher with a given number of rails.
+    A dummy plaintext is created initially with the same length as the ciphertext, 
+    which is iteratively replaced by elements from the rails formed from relevant
+    slices of the ciphertext. A counter starting from 0 advances to keep track of
+    which rail we are currently on. The first and last rail only deal with a single
+    rail, the internal rails are further split into the pieces going down and up.
+    If the number of rails is 1, the ciphertext is returned as the plaintext.
+    """
+    if num_rails == 1:
+        return(ciphertext)
+    output = len(ciphertext)*['-']
+    curr = 0
+    for i in range(num_rails):
+        rail = (len(ciphertext)-1-i)//(2*(num_rails-1)) + 1
+        if (i in range(1, num_rails-1)):
+            rail2 = (len(ciphertext)-1+i)//(2*(num_rails-1))
+            section = ciphertext[curr:(curr+rail+rail2)]
+            output[i::2*(num_rails-1)] = section[::2]
+            output[2*(num_rails-1)-i::2*(num_rails-1)] = section[1::2]
+            curr += rail + rail2
+        else:
+            output[i::2*(num_rails-1)] = ciphertext[curr:(curr+rail)]
+            curr += rail
+    return "".join(output)
+
+def read_from_file(filename):
+    """
+    Reads and returns content from a file.
+    Strips away non-alphanumerical characters and converts letters to uppercase.
+    """
+    with open(filename, 'r') as f:
+        content = f.read()
+    return "".join([x.upper() for x in content if x.isalnum()])
+
+def write_to_file(filename, content):
+    """
+    Writes content to a file. Spacing, punctuation, and casing will be lost.
+    Replaces contents if filename exists, otherwise creates new file for it.
+    """
+    with open(filename, 'w') as f:
+        f.write(content)
+
+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.
+
+    Depending on the input, further prompts will get the relevant parameters,
+    (e.g. shift for Caesar, passkey for Vigenere, number of rails for Railfence)
+    Primary prompts requires only the first letter to match choice, reprompting
+    if not the case. This robustness is not extended to these secondary prompts.
+    Input strings are stripped to alphanumerical characters and converted to uppercase.
+    """
+    input_dict = {"F":"File", "S":"String", "D":"Decrypting", "E":"Encrypting", "C":"Caesar", "V":"Vigenere", "R":"Railfence"}
+
+    print("*Input*")
+    format = input("(F)ile or (S)tring? ").upper()
+    while not format or format[0] not in ['F', 'S']:
+        format = input("Please enter either 'F' for file or 'S' for string: ").upper()
+    if format[0] == "F":
+        filename = input("Filename? ")
+        input_text = read_from_file(filename)
+    else:
+        raw_string = input("Enter the string to encrypt: ")
+        input_text = "".join([x.upper() for x in raw_string if x.isalnum()])
+
+    print("*Transform*")
+    operation = input("(E)ncrypt or (D)ecrypt? ").upper()
+    while not operation or operation[0] not in ['E', 'D']:
+        operation = input("Please enter either 'E' for encrypt or 'D' for decrypt: ").upper()
+    cipher = input("(C)aesar, (V)igenere, or (R)ailfence? ").upper()
+    while not cipher or cipher[0] not in ['C','V','R']:
+        cipher = input("Please enter either 'C' for Caesar, 'V' for Vigenere, or 'R' for Railfence: ").upper()
+    if cipher[0] == "C":
+        shift = input("Shift? (Default is 3): ")
+        if not shift:
+            shift = "3"
+    elif cipher[0] == "V":
+        passkey = input("Passkey? ").upper()
+    else:
+        num_rails = input("Number of rails? ")
+
+    print_list = []
+    print_list.append(input_dict[operation[0]])
+    if format == "F":
+        print_list.append("the contents of")
+        print_list.append(filename)
+    else:
+        print_list.append(input_text)
+    print_list.append("using")
+    print_list.append(input_dict[cipher[0]])
+    print_list.append("cipher with")
+    if cipher[0] == "C":
+        print_list.append("shift of")
+        print_list.append(shift)
+    elif cipher[0] == "V":
+        print_list.append("key")
+        print_list.append(passkey)
+    else:
+        print_list.append(num_rails)
+        print_list.append("rails")
+    print_list.append("...")
+    print(" ".join(print_list))
+
+    print("*Output*")
+    out_format = input("(F)ile or (S)tring? ").upper()
+    while not out_format or out_format[0] not in ['F', 'S']:
+        out_format = input("Please enter either 'F' for file or 'S' for string: ").upper()
+    result = []
+    if operation[0] == "E":
+        if cipher[0] == "C":
+            result = encrypt_caesar(input_text,int(shift))
+        elif cipher[0] == "V":
+            result = encrypt_vigenere(input_text,passkey)
+        else:
+            result = encrypt_railfence(input_text,int(num_rails))
+    else:
+        if cipher[0] == "C":
+            result = decrypt_caesar(input_text,int(shift))
+        elif cipher[0] == "V":
+            result = decrypt_vigenere(input_text,passkey)
+        else:
+            result = decrypt_railfence(input_text,int(num_rails))
+    if out_format[0] == "S":
+        if operation[0] == "E":
+            print("The ciphertext is: " + result)
+        else:
+            print("The plaintext is: " + result)
+    else:
+        out_file = input("Filename? ")
+        write_to_file(out_file, result)
+        if operation[0] == "E":
+            print("Writing ciphertext to " + out_file + " ...")
+        else:
+            print("Writing plaintext to " + out_file + " ...")
+
+# 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()

alandeng-assign1/feedback.txt

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+Name: Alan Deng
+
+
+1) How long did this assignment take you to complete?
+
+
+6-ish hours. run_suite() took longer than expected
+
+
+
+2) What has been the best part of the class so far?
+
+
+
+lectures and labs have been great so far. keep it up! :)
+
+
+
+
+3) What can we do to make this class more enjoyable for you?
+
+
+faster uploads of slides and video would be awesome.
+
+
+
+
+
+4) What types of assignments would excite you in this class?
+
+
+
+
+
+
+more of this stuff! thanks