I created a GMP branch that replaces bignum with GMP. This should eliminate compile errors when using newer versions of libssl. I have tested on Ubuntu 16.04 and 18.04 with libssl 1.1. I was able to sync from scratch and have been running for a couple days with no issues.

I haven't updated the build system. For now you need to compile using ./configure LIBS=-lgmp
Can someone help with this?