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I computed $\Pr[\mathsf{CT} = 1] = \Pr[\mathsf{CT} = 2] = \Pr[\mathsf{CT} = 4] = 2/9$ and $\Pr[\mathsf{CT} = 3] = 1/3$.

When I calculate the first entry in the table, I get 1/2 not 1/9. Is my calculation wrong or is the image wrong?

How do I fill the table and tell if they are independent?

  • $\begingroup$ How did you calculate the first entry in the table? (If you log in, with the link that should have been sent to your email when you first posted, you can edit your original question; you should do that instead of posting an ‘answer’ which is not an answer.) $\endgroup$ – Squeamish Ossifrage Mar 2 '18 at 20:18
  • $\begingroup$ Also you may want to read this help article on how to merge your accounts, in case you only have access to one. $\endgroup$ – SEJPM Mar 3 '18 at 19:34

The table is the joint distribution: $\Pr[\mathsf{CT} = 1 \mathrel{\mathit{and}} \mathsf{PT} = a]$, etc.: What is the fraction of cases in which the ciphertext is $1$ and the plaintext is $a$?

What is the definition of independent for two random variables? This should involve either the joint and marginal distributions, or the conditional and marginal distributions, depending on how you choose to phrase it. How can you use the table you've filled out to ascertain whether the two random variables $\mathsf{PT}$ and $\mathsf{CT}$ are independent?

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