Hi, I think it's a bug in libtommath. Compiling both 2017.75 and 2017.75 with updated libtom*, the latter one works while the original one doesn't. And for other parts, such as kernel, busybox, userspace programs, etc. , all of them are working perfectly. That's the reason why I think it isn't a compiler bug.
Sorry, since I cannot access the router, which means I cannot execute any commands, it's not trivial to get the backtrace. Based on Kevin's report, > ssh -vvv' shows things hanging during the initial ECDH key exchange it might be something wrong with key verification, I'm not sure about it, totally wildly guess. You may want to contact Kevin off-list to know how he finds the issue resides in libtommath, I just follow his guess and replace libtom* to verify his idea. Kevin Darbyshire-Bryant <kevin at darbyshire-bryant.me.uk> Best Regards, Syrone Wong