On Thu, May 19, 2016 at 05:58:11PM +0200, Jakob Bohm wrote: > What kind (and size) of keys are in your certificates? > > That sounds like the most likely issue. Perhaps that dhparam2049.pem does not actually contain a 2048-bit prime. I don't recall a floor on RSA key sizes in 1.0.1. The CHANGES file lists for 1.0.1q: *) Reject DH handshakes with parameters shorter than 1024 bits. [Kurt Roeckx] Otherwise, I don't see any enforcement of key size floors in 1.0.1. > > >- I've set up a PKI with a ca.crt file and a server.crt/server.key > > > keypair Not posting the certs makes it rather difficult to offer any help. > > >- next , I run > >> > >> ~/src/openssl-1.0.1t/apps/openssl s_server -CAfile ca.crt -cert > >>server.crt -key server.key -dhparam dh2048.pem I don't see a "-accept 4433" in that command. > >>- then, with s_client > >> > >> ~/src/openssl-1.0.1t/apps/openssl s_client -CAfile ca.crt -connect > >>127.0.0.1:4433 What's listening on "4433"? > >>and I always end up with > >> > >> Verify return code: 21 (unable to verify the first certificate) > >> > >>If I either change s_server *or* s_client to use openssl 0.9.8 then the > >>above commands work! With 0.9.8 s_client or s_server will be able to use the default CApath that is probably hashed with the 0.9.8-compatible hash algorithm, allowing either or both to construct a more complete chain, Likely the "ca.crt" you're using is not the (immediate?) issuer of the server certificate. -- Viktor.