bambinoh
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 Jun21 awarded Scholar Jun21 comment How can I solve the discrete logarithm modulo 2q+1 if I can solve it in the subgroup of order q? Thanks, that clears it all up. Jun21 accepted How can I solve the discrete logarithm modulo 2q+1 if I can solve it in the subgroup of order q? Jun20 awarded Student Jun20 comment How can I solve the discrete logarithm modulo 2q+1 if I can solve it in the subgroup of order q? That makes sense since the order of $G_q$ is q. Nonetheless, I'm still not sure why I can apply the DLP oracle in $G_q$ to $t^2 = (s^2)^z)$. However some research teaches me that that's a property when $p$ is a safe prime, I'll try to prove that. Thanks for all your help :)! Jun20 comment How can I solve the discrete logarithm modulo 2q+1 if I can solve it in the subgroup of order q? This is the best I can do so far : if I can find $z$ in $(t^2) = (s^2)^z mod p$ by using my oracle in $G_q$ (I don't know why I can do this, but let's assume...). Once I find $z$ it should simply equal $y$, since $t = \sqrt{(s^2)^z} = s^z$, and $t = s^y$, hence $z = y$. But that just doesn't feel right to me :/ Jun20 comment How can I solve the discrete logarithm modulo 2q+1 if I can solve it in the subgroup of order q? Then how can I use my oracle in the subgroup? I think I'm missing some algebra to comprehend what you're trying to say Jun20 comment How can I solve the discrete logarithm modulo 2q+1 if I can solve it in the subgroup of order q? I'm not seeing it yet, but just for clarity, you mean $(t^2) = (s^2)^z\,mod\,q$, not $mod\,p$, right? Jun20 comment How can I solve the discrete logarithm modulo 2q+1 if I can solve it in the subgroup of order q? I see how to use your hint to get to the first solution (more or less), but I already had that :). I still don't see how to use it to calculate mod (2q+1) Jun20 awarded Editor Jun20 revised How can I solve the discrete logarithm modulo 2q+1 if I can solve it in the subgroup of order q? added 612 characters in body Jun20 asked How can I solve the discrete logarithm modulo 2q+1 if I can solve it in the subgroup of order q?