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--- ic:labs:05 [2023/10/01 23:24]
razvan.smadu [Laboratorul 05 - DES]
+++ ic:labs:05 [2023/10/09 23:22] (current)
razvan.smadu
@@ Line 3: / Line 3: @@
 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 și platforma Google Colab, accesând [[https://colab.research.google.com/drive/1Vi5V7mHYIau6vbGFiQITd2FRzYRT3o1j?usp=sharing|acest]] link.
+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>
@@ Line 428: / Line 429: @@
 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):
+def get_index(a: List[bytes], x: bytes) -> int:
-    """Locate the leftmost value exactly equal to x in list a"""
+    """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 444: / Line 457: @@
-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. 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 466: / Line 479: @@
-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. 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)
@@ Line 488: / Line 501: @@
-def des2_enc(k1, k2, m):
+def des2_enc(k1: bytes, k2: bytes, m: bytes) -> bytes:
-    # TODO 3.B: implement des2_enc
+    # TODO B.1: implement des2_enc
-    raise NotImplementedError('Not implemented')
+    raise NotImplementedError("Not implemented")
-def des2_dec(k1, k2, c):
+def des2_dec(k1: bytes, k2: bytes, c: bytes) -> bytes:
-    # TODO 3.B: implement des2_dec
+    # TODO B.2: implement des2_dec
-    raise NotImplementedError('Not implemented')
+    raise NotImplementedError("Not implemented")
-def main():
+def test_des2() -> None:
-    k1 = 'Smerenie'
+    k1 = "Smerenie"
-    k2 = 'Dragoste'
+    k2 = "Dragoste"
-    m1_given = 'Fericiti cei saraci cu duhul, ca'
+    m1_given = "Fericiti cei saraci cu duhul, ca"
-    c1 = 'cda98e4b247612e5b088a803b4277710f106beccf3d020ffcc577ddd889e2f32'
+    c1 = "cda98e4b247612e5b088a803b4277710f106beccf3d020ffcc577ddd889e2f32"
-    c2 = '54826ea0937a2c34d47f4595f3844445520c0995331e5d492f55abcf9d8dfadf'
+    c2 = "54826ea0937a2c34d47f4595f3844445520c0995331e5d492f55abcf9d8dfadf"
-    # TODO 3.C: Decrypt c1 and c2 using k1 and k2, and make sure that
+    # TODO C: Decrypt c1 and c2 using k1 and k2, and make sure that
     #           des2_dec(k1, k2, c1 || c2) == m1 || m2
-    #
-    # Note: The code to decrypt c1 is already provided below. You **need**
+    # 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))
-    m1 = bytes_to_string(des2_dec(string_to_bytes(k1), string_to_bytes(k2),
-                         bytes.fromhex(c1)))
     assert m1 == m1_given, f'Expected "{m1_given}", but got "{m1}"'
-    print('ciphertext:', c1)
+    print("ciphertext:", c1)
-    print('plaintext:', m1)
+    print("plaintext:", m1)
-    print('plaintext in hexa:', str_2_hex(m1))
+    print("plaintext in hexa:", str_2_hex(m1))
-    # TODO 3.D: run meet-in-the-middle attack for the following plaintext/ciphertext
+    # TODO C.2: Decrypt m2 similar to m1. Keep in mind that des_dec()
-    m1 = 'Pocainta'
+    # returns bytes
-    c1 = '9f98dbd6fe5f785d'
+    m2 = ...
-    m2 = 'Iertarea'
-    c2 = '6e266642ef3069c2'
-    # NOTE: you only need to search for the first 2 bytes of the each key (i.e.,
+    print("ciphertext:", c2)
-    # to find out what are the values for each `?`)
+    print("plaintext:", m2)
-    k1 = '??oIkvH5'
+    print("plaintext in hexa:", str_2_hex(m2))
-    k2 = '??GK4EoU'
+    # 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}"'
-if __name__ == '__main__':
-    main()
-</code>
+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/05.1696191855.txt.gz · Last modified: 2023/10/01 23:24 by razvan.smadu

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