Question

1. asap please python
2. 1. Using block diagram, design the architectural layout of the simplified model of a symmetric Cryptosystem.
   2. Implement a cryptosystem columnar transposition technique with a 4 x 4 matrix arrangement. Test your code with ‘cryptography’ as the plaintext.

Answer 1

Answer I)

It is a technique used to avoid an unauthorized access of data. It helps to provide accountability fairness and accuracy and also provide confidentiality. Broadly, four different kinds of people contributed their efforts in this technique and are: (i) Military, (ii) The Diplomatic Corps, (iii) Diarists, and (iv) Communications System. Cryptography involves two basic operations and is named as encryption and key management. Information/data canbe encrypted using a cryptographic algorithm by various keys. The security of cryptographic system is not only
dependent on the encryption algorithm; it also depends upon the keys used for the encryption. These keys area always kept secured from the hacker and are known as secret key. Key plays an important role in encryption process, which is a main part of cryptography . Due to channel impairments sometimes the transmitted data and/or key may get corrupted. If it is slightly changed or corrupted, the data will not be recovered; therefore, key needs to be transported over the secured channel. The frequency of use of a cryptographic key always has a direct correlation to how often the key should be changed. Encryption algorithms can be hacked by utilizing supercomputer which provides fast speed and allows the hacker to use more permutations and combinations in a specified time. Modern era depends upon wireless communication and almost all the electronic funds are being carried out online. In order to protect the same and maintain the privacy of the users; cryptography is the best solution due to their better response even in the presence of advisory. For better security, either more number of keys is used or the length of the existing keys is increased. In both the approaches the overheads are increased, therefore, the best idea is to use sub-keys. Sub-keys are used only for such nodes which are attacked by the hacker. The sub keys are always derived from the main key which helps in reducing the overheads. The basic cryptographic model has been shown in figure 2.1. It involves encryption and decryption section; initially, the data has been encrypted by the help of key and further transmitted over the web. Finally, it has been received and the encrypted data is decrypted with the help of same or different key. The key is any value and/or word and is used in both the sections for encryption and decryption purpose.

Answer II)

# Python3 implementation of

# Columnar Transposition

import math

key = "HACK"

# Encryption

def encryptMessage(msg):

    cipher = ""

    # track key indices

    k_indx = 0

    msg_len = float(len(msg))

    msg_lst = list(msg)

    key_lst = sorted(list(key))

    # calculate column of the matrix

    col = len(key)

     

    # calculate maximum row of the matrix

    row = int(math.ceil(msg_len / col))

    # add the padding character '_' in empty

    # the empty cell of the matix

    fill_null = int((row * col) - msg_len)

    msg_lst.extend('_' * fill_null)

    # create Matrix and insert message and

    # padding characters row-wise

    matrix = [msg_lst[i: i + col]

              for i in range(0, len(msg_lst), col)]

    # read matrix column-wise using key

    for _ in range(col):

        curr_idx = key.index(key_lst[k_indx])

        cipher += ''.join([row[curr_idx] for row in matrix])

        k_indx += 1

    return cipher

# Decryption

def decryptMessage(cipher):

    msg = ""

    # track key indices

    k_indx = 0

    # track msg indices

    msg_indx = 0

    msg_len = float(len(cipher))

    msg_lst = list(cipher)

    # calculate column of the matrix

    col = len(key)

     

    # calculate maximum row of the matrix

    row = int(math.ceil(msg_len / col))

    # convert key into list and sort

    # alphabetically so we can access

    # each character by its alphabetical position.

    key_lst = sorted(list(key))

    # create an empty matrix to

    # store deciphered message

    dec_cipher = []

    for _ in range(row):

        dec_cipher += [[None] * col]

    # Arrange the matrix column wise according

    # to permutation order by adding into new matrix

    for _ in range(col):

        curr_idx = key.index(key_lst[k_indx])

        for j in range(row):

            dec_cipher[j][curr_idx] = msg_lst[msg_indx]

            msg_indx += 1

        k_indx += 1

    # convert decrypted msg matrix into a string

    try:

        msg = ''.join(sum(dec_cipher, []))

    except TypeError:

        raise TypeError("This program cannot","handle repeating words.")

    null_count = msg.count('_')

    if null_count > 0:

        return msg[: -null_count]

    return msg

# Driver Code

msg = "Geeks for Geeks"

cipher = encryptMessage(msg)

print("Encrypted Message: {}". format(cipher))

print("Decryped Message: {}". format(decryptMessage(cipher)))

Output:

Encrypted Message: e  kefGsGsrekoe_
Decrypted Message: Geeks for Geeks

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