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Dec 20, 2016 at 6:38 history tweeted twitter.com/StackCrypto/status/811098376154611712
Dec 19, 2016 at 13:01 vote accept ChaosCoder
Dec 19, 2016 at 12:37 answer added fgrieu timeline score: 3
Dec 19, 2016 at 8:30 comment added ChaosCoder Ah okay, no I don't. That took longer than needed. Why not add an answer to this question?
Dec 19, 2016 at 8:12 comment added fgrieu @ChaosCoder, Hint: do you learn anything about a permutation when given the images $x_j$ of unknown random elements $b_j$ by this permutation?
Dec 18, 2016 at 12:58 comment added ChaosCoder @fgrieu: Could you elaborate on your comment? What does it mean that every $b_j \rightarrow x_j$ is a permutation for my question? Does it help you find $a$?
Dec 17, 2016 at 17:49 comment added fgrieu Knowing $x_1$ really leaves you with $\varphi(p−1)$ possible pairs of numbers, where $\varphi$ is the Euler totient function. Hint: show that for any fixed $a\in\mathbb Z_{p-1}^*$ (the subset of $\mathbb Z_{p-1}$ wich elements are coprime with $p-1$), the function $b_j\to x_j$ is a permutation of $\mathbb Z_{p-1}^*$; conclude.
Dec 17, 2016 at 17:39 history edited fgrieu CC BY-SA 3.0
Add necessary parenthesis
Dec 17, 2016 at 14:02 comment added Geoffroy Couteau With a single pair, you have many possible solution, but the set of valid solutions is easy to compute, it cannot be seen as a hard problem. With two equations, you get the common factor by computing a gcd, and recovering the remaining factors takes one inversion and two modular multiplications then.
Dec 17, 2016 at 13:25 comment added SEJPM This is about the same problem as recovering the private key from DSA signatures: You always have at least one more unknown variable than equations.
Dec 17, 2016 at 10:34 history asked ChaosCoder CC BY-SA 3.0