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For every PPT distinguisher A there exists a negligible function $neg(·)$ such that for all $\lambda$

$|\Pr[A(1^\lambda, g,g_1^a,g_1^b,g_1^{ab}) = 1] - \Pr[A(1^\lambda, g,g_1^a,g_1^b,g_1^z) = 1]| \leq \textsf{negl}(\lambda)$

where $g$ is a generator of group $G$ of order $p$ where $p$ is a prime of length approximately $\lambda$, $g_1 = g^r \in G$, and $r,a,b,z$ are randomly chosen from $Z_p$

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Hint: suppose we modify the problem so that $r, a, b, z$ are selected uniformly randomly from the interval $[1, p-1]$; how do the probability distributions of $(g^{ra}, g^{rb}, g^{rab})$ and $(g^{ra}, g^{rb}, g^{rz})$ compare?

Hint: if we actually select $r, a, b, z$ from $\mathbb{Z}_p$, what is the probability that at least one of them are selected outside the interval $[1, p-1]$? Can you show that this probability is negligible?

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