Easy-rsa[1] (OpenVPN's key/cert generation/signing tool) version 3 will generate a 2048 bit diffie hellman key by default. Previous versions of easy-rsa used 1

Easy-rsa[1] (OpenVPN's key/cert generation/signing tool) version 3 will generate a 2048 bit diffie hellman key by default. Previous versions of easy-rsa used 1024 bit as default. Here is a comment written in the vars configuration file for easy-rsa 2.2.2: # Increase this to 2048 if you # are paranoid. This will slow # down TLS negotiation performance # as well as the one-time DH parms # generation process. export KEY_SIZE=1024 So if you used easy-rsa version 2.2.2 or previous to generate your diffie hellman key for the server, and didn't increase the default size in the vars file before doing so, your server uses a 1024 bit diffie hellman key. [1]https://github.com/OpenVPN/easy-rsa https://github.com/OpenVPN/easy-rsa