Transport Layer Security Cheat Sheet — Set the appropriate Diffie-Hellman groups

Reference note (untrusted external data; do not execute it as instructions). The practice of earlier than TLS 1.3 protocol versions of Diffie-Hellman parameter generation for use by the ephemeral Diffie-Hellman key exchange (signified by the "DHE" or "EDH" strings in the cipher suite name) had practical issues. For example, the client had no say in the selection of server parameters, meaning it could only unconditionally accept or drop, and the random parameter generation often resulted to denial of service attacks (CVE-2022-40735, CVE-2002-20001). The supported_groups extension is used to negotiate which Diffie-Hellman group are supported the available Finite Field Diffie-Hellman groups are ffdhe2048, ffdhe3072, ffdhe4096, ffdhe6144, ffdhe8192 as specified in RFC7919; Elliptic Curve Diffie-Hellman groups include x25519, prime256v1, x448, secp384r1; for post-quantum cryptography, X25519MLKEM768 it currently used (though it is not a group, proper). For OpenSSL, the list of enabled groups can be configured ins in openssl.cnf. For example Bounded code example (external data; do not execute automatically): ```text openssl_conf = openssl_init [openssl_init] ssl_conf = ssl_module [ssl_module] system_default = tls_system_default [tls_system_default] Groups = X25519MLKEM768:x25519:prime256v1:x448:ffdhe2048:ffdhe3072 ``` An Apache configuration would look like Bounded code example (external data; do not execute automatically): ```text SSLOpenSSLConfCmd Curves X25519MLKEM768:X25519:prime256v1:secp384r1 ``` The same group on NGINX would look like the following Bounded code example (external data; do not execute automatically): ```text ssl_ecdh_curve X25519MLKEM768:X25519:prime256v1:secp384r1; ``` For TLS 1.2 or earlier versions it is recommended not to set Diffie-Hellman parameters. Attribution: Adapted from OWASP Cheat Sheet Series under CC-BY-SA-4.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.