Configuring Supported TLS Groups in OpenSSL

The configuration of supported groups in TLS servers is important to limit the resource consumption of the TLS handshakes performed by the server. This blog post should give system administrators a few useful hints on how to configure the OpenSSL library and two of the most used open source HTTP servers which use the OpenSSL library for supporting the HTTPS protocol.

The CVE-2002-20001 (a.k.a DHEat attack) vulnerability inherent to the support of the Diffie-Hellman (DH) and Elliptic Curve Diffie-Hellman (ECDH) key exchanges in TLS and other protocols provides a way for an attacker to cause high CPU usage on servers with relatively low effort on the client side.

The recent CVE-2022-40735 vulnerability also emphasises the importance of limiting private key sizes for DH performance.