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sasc:laboratoare:05 [2017/03/23 11:41] marios.choudary |
sasc:laboratoare:05 [2017/03/23 19:53] (current) marios.choudary |
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| http://cs.curs.pub.ro/2014/pluginfile.php/13095/mod_resource/content/2/sasc_curs4_5.pdf | http://cs.curs.pub.ro/2014/pluginfile.php/13095/mod_resource/content/2/sasc_curs4_5.pdf | ||
| - | ==== Exercise 1 ==== | + | ==== Exercise 1 (2p) ==== |
| Remember DESX defined as the operation DESX( (k1,k2,k3), m) = k1 ⊕ DES(k2, m ⊕ k3), | Remember DESX defined as the operation DESX( (k1,k2,k3), m) = k1 ⊕ DES(k2, m ⊕ k3), | ||
| where k1, k3 have 64 bits (same as input/output of DES) and k2 has 56 bits (DES key size). | where k1, k3 have 64 bits (same as input/output of DES) and k2 has 56 bits (DES key size). | ||
| - | Show an attack on DESX that runs in time $O(2^{120})$. | + | Show a brute force (exhaustive key search) attack on DESX that runs in time $O(2^{120})$. |
| - | ==== Exercise 2 ==== | + | <note tip> |
| + | Try using a couple of (message, ciphertext) pairs and see if you can get rid of k1 | ||
| + | somehow in order to speed up a brute force attack. | ||
| + | </note> | ||
| + | |||
| + | ==== Exercise 2 (3p) ==== | ||
| Show why the following schemes do not bring any real advantage compared to DES: | Show why the following schemes do not bring any real advantage compared to DES: | ||
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| * b) c = DES(k2, m ⊕ k1) | * b) c = DES(k2, m ⊕ k1) | ||
| - | ==== Exercise 3 ==== | + | <note tip> |
| + | You may use a similar approach to what you did in the previous exercise. | ||
| + | </note> | ||
| + | |||
| + | ==== Exercise 3 (5p) ==== | ||
| The goal of this exercise is to implement the meet-in-the-middle attack on double DES. | The goal of this exercise is to implement the meet-in-the-middle attack on double DES. | ||
