Hello and thx for your reply, about the "emunand" term, I think I'm a bit confused, doesn't emunand stands for the nand installed on the sd card inserted in the red gateway ? If it's this, then I tried but my gateway refuse to "boot" on my 3DS since my 3DS is in version 11.14 and it seems it cannot boot my red gateway anymore (I tried and I almost bricked my Luma3DS sysnand by doing so).
About the game saves, yes they are quite important, well for me of course, the most importants are an ocarina of time save with a good progression, and the second important save is a bravely default save, with also a quite good progression. Thing is, those games I have saves of are 7 years old saves, I wanted to play them again as well as a new game "fire emblem fates" but since this last one wasn't compatible with my 4.5 firmware (locked on 3DS launch splashscreen once I tried to execute it from my gateway) then I've read this game is only compatible with at least 10.3 firmware, that what leads me to upgrade my 3DS to a more "recent" type of custom firmware and get rid of gateway, thing is, it was never mentionned about the crypted gateway saves and I discovered, of course, after upgrading my 3DS to 11.14 + last Luma3DS sysnand that my gateway saves weren't in same format and unusable on luma... that's why I'm asking for any help to convert them for luma3ds sysnand ^^