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 Sep 24 awarded Autobiographer Jul 22 awarded Teacher Jul 21 answered Encryption algorithm that produces dummy output on incorrect passwords Jul 21 answered AES multiple devices to server communication Jul 21 awarded Supporter Jul 21 accepted Security equivalent to Diffie–Hellman problem? Jul 20 asked Security equivalent to Diffie–Hellman problem? Jul 18 revised Given $g$, $b$, $g^{ab}$, is finding $g^a$ a hard problem? added 60 characters in body Jul 18 comment Given $g$, $b$, $g^{ab}$, is finding $g^a$ a hard problem? Is this true if we compute $c = b^-1$ in $Z_r$ and then compute ${g^{ab}}^c$ to get $g^a$? Jul 18 awarded Scholar Jul 18 accepted Given $g$, $b$, $g^{ab}$, is finding $g^a$ a hard problem? Jul 17 comment Given $g$, $b$, $g^{ab}$, is finding $g^a$ a hard problem? @fgrieu no wait, in your example obviously 1 in $Z_3$ but 4 isn't right? Isn't a group member of $Z_r$ smaller than the $r$? Jul 17 comment Given $g$, $b$, $g^{ab}$, is finding $g^a$ a hard problem? @fkraiem Sorry, but do you have any example in mind? Jul 17 comment Given $g$, $b$, $g^{ab}$, is finding $g^a$ a hard problem? @fkraiem $r$ is just a prime number, and $Z_r$ is a group. So yes the exponent $ab$ should be in $Z_r$.. Jul 17 revised Given $g$, $b$, $g^{ab}$, is finding $g^a$ a hard problem? added 65 characters in body Jul 17 comment Given $g$, $b$, $g^{ab}$, is finding $g^a$ a hard problem? @fgrieu its just a mathematics group, am I having something confusing here? en.wikipedia.org/wiki/Group_(mathematics) Jul 17 awarded Student Jul 17 comment Given $g$, $b$, $g^{ab}$, is finding $g^a$ a hard problem? @fgrieu $a$ and $b$ are group elements of $Z_r$, and $a.b$ should be computed in that group. Jul 17 comment Given $g$, $b$, $g^{ab}$, is finding $g^a$ a hard problem? @curious p is known, and r is known also. Jul 17 awarded Editor