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2

In short, yes. The complementation property of DES states that if $DES_K(P) = C$, then $DES_{\overline{K}}(\overline{P}) = \overline{C}$, where $\overline{X}$ is the complement of a string $X$. ECB with DES takes a message $M_1M_2\cdots M_\ell$ and computes $C_1C_2\cdots C_\ell$, where $C_i = DES_K(M_i)$, for $1\le i\le\ell$. Therefore, if you encrypt ...

-1

And here is a simple calculation time for brute force 56 bits DES key with a Laptop. Immagine your laptop execute one DES in $1 \mu s$, which is very optimist. To Explore the $2^{56}$ key space, it costs $2^{56} \; \mu sec$, which is approximativelly $0,72. 10^{17}\; \mu sec$. converting this quantity in hours, days and years, you need approximativelly \$2. ...

6

DES with 2 rounds is broken. It is trivial to find a way to get the key with much less work than for the full DES (and even that is broken). DES is a Feistel cipher, so we have two halves, the left and the right half. For every round, we do something with the one half and a subkey, and then XOR it with the other half. After that we switch both halves, ...

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