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1

Not necessarily. Let $M$ be a secure deterministic MAC like HMAC-SHA256. Define the randomized MAC $M'_{k, \rho}(m) := M_k(m) \mathbin\| \rho$; that is, $M'$ just appends the randomization to the MAC. Then encrypt-and-authenticate with $M'$ still leaks message equality, even though the MAC is technically randomized.

1

Would it be OK if the iv used in handshake gets repeated considering the plain text is a random number? No, it would definitely not be OK. Reusing the IV will allow the attacker to recover the internal GCM H value - this will allow the attacker to make arbitrary modifications to encrypted messages. For static keying (or anywhere else where it's difficult ...

0

$v_1 = b \cdot z \\ v_2 = b + z^{-1}$ Given the following equations, we can rearrange the following into: $v_1 \cdot z^{-1} = b \\ v_2 - z^{-1} = b \\ v_1 \cdot z^{-1} = v_2 - z^{-1} \\ v_1 \cdot z^{-1} + z^{-1} = v_2 \\ z^{-1} (v_1 + 1) = v_2 \\ v_1 + 1 = v_2 * z \hspace{50pt} \text{(multiply both side by z)} \\ z = (v_1 + 1) \cdot (v_2)^{-1}$ Once ...

2

A fun one(and how I was introduced to MPC) could be to compute the average constipation rate of the class or something like that, where each student has a constipation rate between 0 and 100. This could be done using a sum protocol initialized with random value written on a piece of paper. The value is chosen by the teacher; upon receiving a paper, the ...

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Here's a simple example for addition which can be extended to other operations as well. Suppose there $X$ number of children in a classroom and everyone has a score ranging from 0 to 100. We want to calculate the average of the scores of all students without the teacher or the other students knowing what their classmates have scored. Here's how we can ...

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