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--- ic:labs:05 [2021/11/01 15:51]
razvan.smadu [Exercitiul 3 (5p)]
+++ ic:labs:05 [2023/10/09 23:22] (current)
razvan.smadu
@@ Line 1: / Line 1: @@
 ===== Laboratorul 05 - DES =====
-In acest laborator vom face niste exercitii ce folosesc algoritmul DES si variatii ale acestuia discutate la [[https://drive.google.com/file/d/1Fjybv6k5QudRB1bkAi5shVUGlUyTO_0U/view|curs]].
+În acest laborator vom face niște exerciții ce folosesc algoritmul DES și variații ale acestuia discutate la [[https://drive.google.com/file/d/1Fjybv6k5QudRB1bkAi5shVUGlUyTO_0U/view|curs]].
 Prezentarea PowerPoint pentru acest laborator poate fi găsită [[https://drive.google.com/file/d/1FU422fCHM24fRnMuzFd0OjhQqT6AQZ3X/view?usp=sharing|aici]].
+Puteți lucra acest laborator folosind platforma Google Colab, accesând [[https://colab.research.google.com/github/ACS-IC-labs/IC-labs/blob/main/labs/lab05/lab5.ipynb|acest]] link.
+<hidden>
+<spoiler Click pentru a vedea utils.py>
 <file python utils.py>
 import base64
+from typing import Generator
-# CONVERSION FUNCTIONS
-def _chunks(string, chunk_size):
-    for i in range(0, len(string), chunk_size):
+def _pad(data: str, size: int) -> str:
-        yield string[i:i+chunk_size]
+    reminder = len(data) % size
+    if reminder != 0:
-def byte_2_bin(bval):
+        data = "0" * (size - reminder) + data
-    """
+    return data
-      Transform a byte (8-bit) value into a bitstring
+def _chunks(data: str, chunk_size: int) -> Generator[str, None, None]:
+    data = _pad(data, chunk_size)
+    for i in range(0, len(data), chunk_size):
+        yield data[i : i + chunk_size]
+def _hex(data: int) -> str:
+    return format(data, "02x")
+# Conversion functions
+def byte_2_bin(bval: int) -> str:
+    """Converts a byte value to a binary string.
+    Args:
+        bval (int):
+            The byte value to be converted. It should be an integer between
+and 255.
+    Returns:
+        str: The binary string representation of the byte value, where each bit
+        is encoded as a character. The result has a fixed length of 8 characters
+        and is padded with leading zeros if necessary.
+    Examples:
+        >>> byte_2_bin(72)
+        '01001000'
+        >>> byte_2_bin(66)
+        '01000010'
     """
     return bin(bval)[2:].zfill(8)
-def _hex(x):
-    return format(x, '02x')
+def hex_2_bin(data: str) -> str:
+    """Converts a hexadecimal string to a binary representation.
-def hex_2_bin(data):
-    return ''.join(f'{int(x, 16):08b}' for x in _chunks(data, 2))
+    Args:
+        data (str): The hexadecimal string to be converted. It should have an
-def str_2_bin(data):
+            even number of characters and only contain valid hexadecimal digits
-    return ''.join(f'{ord(c):08b}' for c in data)
+            (0-9, A-F, a-f).
-def bin_2_hex(data):
+    Returns:
-    return ''.join(f'{int(b, 2):02x}' for b in _chunks(data, 8))
+        str: The binary representation of the hexadecimal string, where each
+            pair of hexadecimal digits is encoded as an 8-bit binary number.
-def str_2_hex(data):
-    return ''.join(f'{ord(c):02x}' for c in data)
+    Examples:
+        >>> hex_2_bin("01abcd")
-def bin_2_str(data):
+        '000000011010101111001101'
-    return ''.join(chr(int(b, 2)) for b in _chunks(data, 8))
+        >>> hex_2_bin("0a")
+        '00001010'
-def hex_2_str(data):
+    """
-    return ''.join(chr(int(x, 16)) for x in _chunks(data, 2))
+    return "".join(f"{int(x, 16):08b}" for x in _chunks(data, 2))
-# XOR FUNCTIONS
-def strxor(a, b):  # xor two strings, trims the longer input
+def bin_2_hex(data: str) -> str:
-    return ''.join(chr(ord(x) ^ ord(y)) for (x, y) in zip(a, b))
+    """Converts a binary string to a hexadecimal representation.
-def bitxor(a, b):  # xor two bit-strings, trims the longer input
+    Args:
-    return ''.join(str(int(x) ^ int(y)) for (x, y) in zip(a, b))
+        data (str): The binary string to be converted. It should have a multiple
+            of 8 characters and only contain valid binary digits (0 or 1).
-def hexxor(a, b):  # xor two hex-strings, trims the longer input
-    return ''.join(_hex(int(x, 16) ^ int(y, 16)) for (x, y) in zip(_chunks(a, 2), _chunks(b, 2)))
+    Returns:
+        str: The hexadecimal representation of the binary string, where each
-# BASE64 FUNCTIONS
+            group of 8 binary digits is encoded as a pair of hexadecimal digits.
-def b64decode(data):
-    return bytes_to_string(base64.b64decode(string_to_bytes(data)))
+    Examples:
+        >>> bin_2_hex("000000011010101111001101")
-def b64encode(data):
+        '01abcd'
+        >>> bin_2_hex("00001010")
+        '0a'
+    """
+    return "".join(f"{int(b, 2):02x}" for b in _chunks(data, 8))
+def str_2_bin(data: str) -> str:
+    """Converts a string to a binary representation.
+    Args:
+        data (str): The string to be converted.
+    Returns:
+        str: The binary representation of the string, where each character is
+            encoded as an 8-bit binary number.
+    Examples:
+        >>> str_2_bin("Hello")
+        '0100100001100101011011000110110001101111'
+        >>> str_2_bin("IC")
+        '0100100101000011'
+    """
+    return "".join(f"{ord(c):08b}" for c in data)
+def bin_2_str(data: str) -> str:
+    """Converts a binary string to a string.
+    Args:
+        data (str): The binary string to be converted. It should have a multiple
+            of 8 characters and only contain valid binary digits (0 or 1).
+    Returns:
+        str: The string representation of the binary string, where each group
+            of 8 binary digits is decoded as a character.
+    Examples:
+        >>> bin_2_str("0100100001100101011011000110110001101111")
+        'Hello'
+        >>> bin_2_str("0100100101000011")
+        'IC'
+    """
+    return "".join(chr(int(b, 2)) for b in _chunks(data, 8))
+def str_2_hex(data: str) -> str:
+    """Converts a string to a hexadecimal representation.
+    Args:
+        data (str): The string to be converted.
+    Returns:
+        str: The hexadecimal representation of the string, where each character
+            is encoded as a pair of hexadecimal digits.
+    Examples:
+        >>> str_2_hex("Hello")
+        '48656c6c6f'
+        >>> str_2_hex("IC")
+        '4943'
+    """
+    return "".join(f"{ord(c):02x}" for c in data)
+def hex_2_str(data: str) -> str:
+    """Converts a hexadecimal string to a string.
+    Args:
+        data (str): The hexadecimal string to be converted. It should have an
+            even number of characters and only contain valid hexadecimal digits
+            (0-9, A-F, a-f).
+    Returns:
+        str: The string representation of the hexadecimal string, where each
+            pair of hexadecimal digits is decoded as a character.
+    Examples:
+        >>> hex_2_str("48656c6c6f")
+        'Hello'
+        >>> hex_2_str("4943")
+        'IC'
+    """
+    return "".join(chr(int(x, 16)) for x in _chunks(data, 2))
+# XOR functions
+def strxor(operand_1: str, operand_2: str) -> str:
+    """Performs a bitwise exclusive OR (XOR) operation on two strings.
+    Args:
+        operand_1 (str): The first string to be XORed.
+        operand_2 (str): The second string to be XORed.
+    Returns:
+        str: The result of the XOR operation on the two strings, where each
+            character is encoded as an 8-bit binary number. The result has
+            the same length as the shorter input string.
+    Examples:
+        >>> strxor("Hello", "IC")
+        '\\x01&'
+        >>> strxor("secret", "key")
+        '\\x18\\x00\\x1a'
+    """
+    return "".join(chr(ord(x) ^ ord(y)) for (x, y) in zip(operand_1, operand_2))
+def bitxor(operand_1: str, operand_2: str) -> str:
+    """Performs a bitwise exclusive OR (XOR) operation on two bit-strings.
+    Args:
+        operand_1 (str): The first bit-string to be XORed. It should only
+            contain valid binary digits (0 or 1).
+        operand_2 (str): The second bit-string to be XORed. It should only
+            contain valid binary digits (0 or 1).
+    Returns:
+        str: The result of the XOR operation on the two bit-strings, where each
+            bit is encoded as a character. The result has the same length as
+            the shorter input bit-string.
+    Examples:
+        >>> bitxor("01001000", "01000010")
+        '00001010'
+        >>> bitxor("10101010", "00110011")
+        '10011001'
+    """
+    return "".join(str(int(x) ^ int(y)) for (x, y) in zip(operand_1, operand_2))
+def hexxor(operand_1: str, operand_2: str) -> str:
+    """Performs a bitwise exclusive OR (XOR) operation on two hexadecimal
+    strings.
+    Args:
+        operand_1 (str): The first hexadecimal string to be XORed. It should
+            have an even number of characters and only contain valid hexadecimal
+            digits (0-9, A-F, a-f).
+        operand_2 (str): The second hexadecimal string to be XORed. It should
+            have an even number of characters and only contain valid
+            digits (0-9, A-F, a-f).
+    Returns:
+        str: The result of the XOR operation on the two hexadecimal strings,
+            where each pair of hexadecimal digits is encoded as a pair of
+            hexadecimal digits. The result has the same length as the shorter
+            input hexadecimal string.
+    Examples:
+        >>> hexxor("48656c6c6f", "42696e67")
+        '0a0c020b'
+        >>> hexxor("736563726574", "6b6579")
+        '18001a'
+    """
+    return "".join(
+        _hex(int(x, 16) ^ int(y, 16))
+        for (x, y) in zip(_chunks(operand_1, 2), _chunks(operand_2, 2))
+    )
+# Python3 'bytes' functions
+def bytes_to_string(bytes_data: bytearray | bytes) -> str:
+    """Converts a byte array or a byte string to a string.
+    Args:
+        bytes_data (bytearray | bytes): The byte array or the byte string to be
+            converted. It should be encoded in UTF-8 format.
+    Returns:
+        str: The string representation of the byte array or the byte string,
+            decoded using UTF-8 encoding.
+    Examples:
+        >>> bytes_to_string(b'Hello')
+        'Hello'
+        >>> bytes_to_string(bytearray(b'IC'))
+        'IC'
+    """
+    return bytes_data.decode(encoding="utf-8")
+def string_to_bytes(string_data: str) -> bytes:
+    """Converts a string to a byte string.
+    Args:
+        string_data (str): The string to be converted.
+    Returns:
+        bytes: The byte string representation of the string, encoded using
+        UTF-8 encoding.
+    Examples:
+        >>> string_to_bytes('Hello')
+        b'Hello'
+        >>> string_to_bytes('IC')
+        b'IC'
+    """
+    return string_data.encode(encoding="utf-8")
+# Base64 functions
+def b64encode(data: str) -> str:
+    """Encodes a string to base64.
+    Parameters:
+        data (str): The string to be encoded.
+    Returns:
+        str: The base64 encoded string, using UTF-8 encoding.
+    Examples:
+        >>> b64encode("Hello")
+        'SGVsbG8='
+        >>> b64encode("IC")
+        'SUM='
+    """
     return bytes_to_string(base64.b64encode(string_to_bytes(data)))
-# PYTHON3 'BYTES' FUNCTIONS
-def bytes_to_string(bytes_data):
-    return bytes_data.decode()  # default utf-8
-def string_to_bytes(string_data):
-    return string_data.encode()  # default utf-8
-</file>
-==== Exercitiul 1 (2p) ====
+def b64decode(data: str) -> str:
+    """Decodes a base64 encoded string.
+    Args:
+        data (str): The base64 encoded string to be decoded. It should only
+            contain valid base64 characters (A-Z, a-z, 0-9, +, /, =).
+    Returns:
+        str: The decoded string, using UTF-8 encoding.
+    Examples:
+        >>> b64decode("SGVsbG8=")
+        'Hello'
+        >>> b64decode("SUM=")
+        'IC'
+    """
+    return bytes_to_string(base64.b64decode(string_to_bytes(data)))
+</file>
+</spoiler>
+==== Exercițiul 1 (2p) ====
 DESX este definit sub forma DESX( (k1,k2,k3), m) = k1 ⊕ DES(k2, m ⊕ k3).
-Construiti un atac impotriva DESX care sa ruleze intr-un timp proportional cu 2<sup>120</sup>.
+Construiți un atac împotriva DESX care să ruleze într-un timp proporțional cu 2<sup>120</sup>.
-==== Exercise 2 (3p) ====
+==== Exercițiul 2 (3p) ====
-De ce urmatoarele scheme nu aduc nicio imbunatatire fata de DES? Justificati!
+De ce următoarele scheme nu aduc nicio îmbunătățire față de DES? Justificați!
   * a) c = k1 ⊕ DES(k2, m)
   * b) c = DES(k2, m ⊕ k1)
-<note tip>Puteti folosi mai multe perechi (mesaj, ciphertext).</note>
+<note tip>Puteți folosi mai multe perechi (mesaj, ciphertext).</note>
-==== Exercitiul 3 (5p) ====
-Scopul acestui exercitiu este de a implementa atacul meet-in-the-middle pe 2DES.
+==== Exercițiul 3 (5p) ====
-Porniti de la scheletul de laborator (vezi mai jos) care se foloseste de biblioteca pycrypto.
-Realizati urmatoarele sarcini:
+Scopul acestui exercițiu este de a implementa atacul meet-in-the-middle pe 2DES.
+Porniți de la scheletul de laborator (vezi mai jos) care se folosește de biblioteca pycrypto.
-=== A. Instalati biblioteca pycrypto ===
+Realizați următoarele sarcini:
+=== A. Instalați biblioteca pycrypto ===
 Vezi https://pypi.org/project/pycryptodome/
-=== B. Implementati 2DES ===
+=== B. Implementați 2DES (1p) ===
-Pornind de la schelet, implementati metodele des2_enc si des2_dec folosind double-DES (2DES).
+Pornind de la schelet, implementați metodele des2_enc si des2_dec folosind double-DES (2DES).
 DES( (k1,k2), m) = DES(k1, DES(k2, m))
-=== C. Testati 2DES ===
+=== C. Testați 2DES (1p) ===
-Folositi urmatoarele ciphertexts
+Folosiți următoarele ciphertexts
 c1 = 'cda98e4b247612e5b088a803b4277710f106beccf3d020ffcc577ddd889e2f32'
@@ Line 103: / Line 373: @@
 c2 = '54826ea0937a2c34d47f4595f3844445520c0995331e5d492f55abcf9d8dfadf'
-Decriptati-le folosind cheile:
+Decriptați-le folosind cheile:
 k1 = 'Smerenie'
@@ Line 109: / Line 379: @@
 k2 = 'Dragoste'
-Primul plaintext corespunzator lui c1 este m1='Fericiti cei saraci cu duhul, ca'. Gasiti al doilea plaintext m2 ce ii corespunde lui c2.
+Primul plaintext corespunzator lui c1 este m1='Fericiti cei saraci cu duhul, ca'. Găsiți al doilea plaintext m2 ce îi corespunde lui c2.
 <note>
-In biblioteca Pycrypto, DES primeste o cheie pe 8 octeti (64 biti) chiar daca ar trebui sa primeasca numai 7 octeti (56 biti). Ultimul bit din fiecare octet este considerat ca fiind un bit de paritate, dar este ignorat de biblioteca. Astfel cheia ce se foloseste va fi intr-adevar de dimensiunea 56 biti. Pentru simplitate insa, in acest exercitiu vom considera ca dimensiunea cheiei este de 64 biti. Astfel putem folosi cheile de 8 caractere de mai sus pentru DES.
+În biblioteca Pycrypto, DES primește o cheie pe 8 octeți (64 biți) chiar dacă ar trebui să primeasca numai 7 octeti (56 biti). Ultimul bit din fiecare octet este considerat ca fiind un bit de paritate, dar este ignorat de bibliotecă. Astfel cheia ce se folosește va fi într-adevăr de dimensiunea 56 biți. Pentru simplitate însă, în acest exercițiu vom considera că dimensiunea cheiei este de 64 biți. Astfel putem folosi cheile de 8 caractere de mai sus pentru DES.
-Vom considera de asemenea ca initializam DES-ul cu valorile default (i.e. modul ECB si niciun IV).
+Vom considera de asemenea că inițializăm DES-ul cu valorile default (i.e. modul ECB și niciun IV).
 </note>
-Decriptati intregul ciphertext (c1 || c2) cu cheile k1 si k2 folosind 2DES si asigurati-va ca rezultatul dat este mesajul initial m1||m2.
+Decriptați întregul ciphertext (c1 || c2) cu cheile k1 și k2 folosind 2DES și asigurați-vă că rezultatul dat este mesajul inițial m1||m2.
-=== D. Implementati atacul meet-in-the-middle pentru 2DES ===
+=== D. Implementați atacul meet-in-the-middle pentru 2DES (3p) ===
-In ultimul si cel mai important pas vi se dau niste perechi plaintext/ciphertext obtinute prin criptarea cu 2DES cu niste chei necunoscute:
+În ultimul și cel mai important pas vi se dau niște perechi plaintext/ciphertext obținute prin criptarea cu 2DES cu niște chei necunoscute:
-m1 = 'Pocainta' (in byte string, i.e. poate fi dat direct ca parametru catre pycrypto DES)
+m1 = 'Pocainta' (în byte string, i.e. poate fi dat direct ca parametru către pycrypto DES)
-c1 = '9f98dbd6fe5f785d' (in hex string, trebuie sa il decodificati mai intai)
+c1 = '9f98dbd6fe5f785d' (în hex string, trebuie să îl decodificați mai întâi)
 m2 = 'Iertarea'
@@ Line 131: / Line 401: @@
 c2 = '6e266642ef3069c2'
-Vi se mai dau si ultimii 6 bytes ale celor 2 chei (care sunt altele decat cele folosite la pasii anteriori):
+Vi se mai dau și ultimii 6 bytes ale celor 2 chei (care sunt altele decat cele folosite la pașii anteriori):
 k1 (last 6 bytes) = 'oIkvH5'
@@ Line 137: / Line 407: @@
 k2 (last 6 bytes) = 'GK4EoU'
-Sarcina voastra este sa gasiti restul octetilor din k1 si k2 aplicand atacul meet-in-the-middle.
+Sarcina voastră este să găsiți restul octeților din k1 și k2 aplicând atacul meet-in-the-middle.
-Your task is now to find the full keys k1 and k2 by applying the meet-in-the-middle attack over 2DES.
-Pentru a construi un tabel, recomandam sa folositi o lista de tupluri unde adaugati perechi de forma (cheie, encriptie) ca in urmatorul exemplu:
+Pentru a construi un tabel, recomandăm să folosiți o lista de tupluri unde adăugați perechi de forma (cheie, encripție) ca în următorul exemplu:
 <code>
 tb = []
@@ Line 151: / Line 420: @@
 </code>
-Pentru a realiza cautare binara in tabel, selectati mai intai a doua coloana (pentru a cauta dupa encriptie):
+Pentru a realiza căutarea binară în tabel, selectați mai întâi a doua coloană (pentru a căuta după encripție):
 <code>
 tenc = [value for _,value in tbs]
 </code>
-iar apoi folositi biblioteca bisect  (e.g. bisect.bisect_left):
+iar apoi folosiți biblioteca bisect (e.g. bisect.bisect_left):
 https://docs.python.org/2/library/bisect.html
 Scheletul de cod:
-<code python desmitm.py>
+<spoiler Click pentru a vedea lab05.py>
-from utils import *
+<file python lab05.py>
-from operator import itemgetter
 import bisect
+from operator import itemgetter
+from typing import List
 from Crypto.Cipher import DES
+from utils import *
-def get_index(a, x):
-    """Locate the leftmost value exactly equal to x in list a"""
+def get_index(a: List[bytes], x: bytes) -> int:
+    """Locate the leftmost value exactly equal to x in list a
+    Args:
+        a (List[bytes]): the list in which to search
+        x (bytes): the value to be searched
+    Returns:
+        int: The leftmost index at which the value is found in the list,
+            or -1 if not found
+    """
     i = bisect.bisect_left(a, x)
     if i != len(a) and a[i] == x:
@@ Line 174: / Line 456: @@
         return -1
-def des_enc(k, m):
+def des_enc(k: bytes, m: bytes) -> bytes:
     """
     Encrypt a message m with a key k using DES as follows:
     c = DES(k, m)
-    Args:
-        m should be a bytestring (i.e. a sequence of characters such as 'Hello' or '\x02\x04')
-        k should be a bytestring of length exactly 8 bytes.
     Note that for DES the key is given as 8 bytes, where the last bit of
-    each byte is just a parity bit, giving the actual key of 56 bits, as expected for DES.
+    each byte is just a parity bit, giving the actual key of 56 bits, as
-    The parity bits are ignored.
+    expected for DES. The parity bits are ignored.
+    Args:
+        k (str): bytestring of length exactly 8 bytes.
+        m (str): bytestring containing the message (i.e. a sequence of
+            characters such as 'Hello' or '\x02\x04')
     Return:
-        The bytestring ciphertext c
+        bytes: The bytestring ciphertext c
     """
     d = DES.new(k, DES.MODE_ECB)
@@ Line 194: / Line 478: @@
     return c
-def des_dec(k, c):
+def des_dec(k: bytes, c: bytes) -> bytes:
     """
     Decrypt a message c with a key k using DES as follows:
     m = DES(k, c)
-    Args:
-        c should be a bytestring (i.e. a sequence of characters such as 'Hello' or '\x02\x04')
-        k should be a bytestring of length exactly 8 bytes.
     Note that for DES the key is given as 8 bytes, where the last bit of
-    each byte is just a parity bit, giving the actual key of 56 bits, as expected for DES.
+    each byte is just a parity bit, giving the actual key of 56 bits, as
-    The parity bits are ignored.
+    expected for DES. The parity bits are ignored.
+    Args:
+        k (str): bytestring of length exactly 8 bytes.
+        c (str): bytestring containing the ciphertext (i.e. a sequence of
+            characters such as 'Hello' or '\x02\x04')
     Return:
-        The bytestring plaintext m
+        bytes: The bytestring plaintext m
     """
     d = DES.new(k, DES.MODE_ECB)
     m = d.decrypt(c)
     return m
-def main():
-    # Exercitiu pentru test des2_enc
-    key1 = 'Smerenie'
-    key2 = 'Dragoste'
-    m1_given = 'Fericiti cei saraci cu duhul, ca'
-    c1 = 'cda98e4b247612e5b088a803b4277710f106beccf3d020ffcc577ddd889e2f32'
-    # TODO: implement des2_enc and des2_dec
-    m1 = des2_dec(key1, key2, hex_2_str(c1))
-    print('ciphertext: ' + c1)
-    print('plaintext: ' + m1)
-    print('plaintext in hexa: ' + str_2_hex(m1))
-    # TODO: run meet-in-the-middle attack for the following plaintext/ciphertext
-    m1 = 'Pocainta'
-    c1 = '9f98dbd6fe5f785d' # in hex string
-    m2 = 'Iertarea'
-    c2 = '6e266642ef3069c2'
-    # Note: you only need to search for the first 2 bytes of the each key:
-    k1 = '??oIkvH5'
-    k2 = '??GK4EoU'
-if __name__ == "__main__":
+def des2_enc(k1: bytes, k2: bytes, m: bytes) -> bytes:
-    main()
+    # TODO B.1: implement des2_enc
-</code>
+    raise NotImplementedError("Not implemented")
+def des2_dec(k1: bytes, k2: bytes, c: bytes) -> bytes:
+    # TODO B.2: implement des2_dec
+    raise NotImplementedError("Not implemented")
+def test_des2() -> None:
+    k1 = "Smerenie"
+    k2 = "Dragoste"
+    m1_given = "Fericiti cei saraci cu duhul, ca"
+    c1 = "cda98e4b247612e5b088a803b4277710f106beccf3d020ffcc577ddd889e2f32"
+    c2 = "54826ea0937a2c34d47f4595f3844445520c0995331e5d492f55abcf9d8dfadf"
+    # TODO C: Decrypt c1 and c2 using k1 and k2, and make sure that
+    #           des2_dec(k1, k2, c1 || c2) == m1 || m2
+    # TODO C.1: Convert k1, k2, c1, and c2 to bytes. It may make the exercise
+    # easier to implement. Use string_to_bytes() for plain texts (i.e., string
+    # in human-readable format), and bytes.fromhex() for hex strings.
+    k1 = ...
+    k2 = ...
+    c1 = ...
+    c2 = ...
+    # NOTE: The code to decrypt c1 is already provided below. You **need**
+    # to decrypt c2 as well.
+    m1 = bytes_to_string(des2_dec(k1, k2, c1))
+    assert m1 == m1_given, f'Expected "{m1_given}", but got "{m1}"'
+    print("ciphertext:", c1)
+    print("plaintext:", m1)
+    print("plaintext in hexa:", str_2_hex(m1))
+    # TODO C.2: Decrypt m2 similar to m1. Keep in mind that des_dec()
+    # returns bytes
+    m2 = ...
+    print("ciphertext:", c2)
+    print("plaintext:", m2)
+    print("plaintext in hexa:", str_2_hex(m2))
+    # TODO C.3: Just to make sure you implemented the task correctly:
+    #           des2_dec(k1, k2, c1 || c2) == m1 || m2
+    m12 = ...
+    assert m12 == m1 + m2, f'Expected "{m12}" to equal "{m1 + m2}"'
+def mitm() -> None:
+    # TODO D: run meet-in-the-middle attack for the following plaintext/ciphertext
+    m1 = "Pocainta"
+    c1 = "9f98dbd6fe5f785d"
+    m2 = "Iertarea"
+    c2 = "6e266642ef3069c2"
+    # TODO D.1: Convert m1, m2, c1, and c2 to bytes. It may make the exercise
+    # easier to implement. Use string_to_bytes() for plain texts (i.e., string
+    # in human-readable format), and bytes.fromhex() for hex strings.
+    m1 = ...
+    c1 = ...
+    m2 = ...
+    c2 = ...
+    # NOTE: You only need to search for the first 2 bytes of the each key (i.e.,
+    # to find out what are the values for each `?`).
+    k1 = "??oIkvH5"
+    k2 = "??GK4EoU"
+    # TODO D.2: Generate the table containing (k2, DES(k2, m1)), for every
+    # possible k2. Use a List[Tuple[bytes, bytes]] for the table (see task
+    # description above).
+    # TODO D.3: Sort the table based on the ciphertexts. Extract the ciphertexts
+    # in a list  (see task description above).
+    # TODO D.4: Perform binary search for all possible k1, such that .
+    # Save the set of candidate keys (k1, k2) in a list.
+    # TODO D.5: From the set of candidate keys, print the ones matching
+    # the second constraint: 2DES(k1, k2, m2) == c2
+def main() -> None:
+    test_des2()
+    mitm()
+if __name__ == "__main__":
+    main()</file>
+</spoiler>
+</hidden>

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ic/labs/05.1635774708.txt.gz · Last modified: 2021/11/01 15:51 by razvan.smadu

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