[pki] Add documentation and check for NULLs
[pki] Add documentation and check for NULLs

nviennot/libssh,sebadoom/libssh,taikoo/libssh,sebadoom/libssh,pouete/libssh,rofl0r/libssh,bigcat26/libssh-mod,rofl0r/libssh,wangshawn/libssh,mwgoldsmith/libssh,bigcat26/libssh-mod,Distrotech/libssh,sebadoom/libssh,kedazo/libssh,nviennot/libssh,wangshawn/libssh,DouglasHeriot/libssh,mwgoldsmith/ssh,nviennot/libssh,wangshawn/libssh,mwgoldsmith/ssh,kedazo/libssh,nviennot/libssh,pouete/libssh,jt1/honeypot-libssh,rofl0r/libssh,sebadoom/libssh,jt1/honeypot-libssh,mwgoldsmith/libssh,taikoo/libssh,robxu9/libssh,pouete/libssh,DouglasHeriot/libssh,mwgoldsmith/libssh,wangshawn/libssh,bigcat26/libssh-mod,jt1/honeypot-libssh,taikoo/libssh,taikoo/libssh,Distrotech/libssh,Distrotech/libssh,DouglasHeriot/libssh,Distrotech/libssh,pouete/libssh,kedazo/libssh,DouglasHeriot/libssh,bigcat26/libssh-mod,elastichosts/libssh,mwgoldsmith/libssh,rofl0r/libssh,robxu9/libssh,robxu9/libssh,jt1/honeypot-libssh,mwgoldsmith/ssh,mwgoldsmith/ssh,elastichosts/libssh,kedazo/libssh,robxu9/libssh,elastichosts/libssh