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SSL_SET_PSK_USE_SESSION_CALLBACK(3) FreeBSD Library Functions Manual NAME SSL_set_psk_use_session_callback, SSL_psk_use_session_cb_func - set TLS pre-shared key client callback SYNOPSIS #include <openssl/ssl.h> typedef int (*SSL_psk_use_session_cb_func)(SSL *ssl, const EVP_MD *md, const unsigned char **id, size_t *idlen, SSL_SESSION **session); void SSL_set_psk_use_session_callback(SSL *ssl, SSL_psk_use_session_cb_func cb); DESCRIPTION LibreSSL provides the stub function SSL_set_psk_use_session_callback() to allow compiling application programs that contain optional support for TLSv1.3 pre-shared keys. LibreSSL does not support TLS pre-shared keys, and no action occurs when SSL_set_psk_use_session_callback() is called. In particular, both arguments are ignored. During session negotiation, LibreSSL never calls the callback cb and always behaves as if that callback succeeded and set the *session pointer to NULL. That is, LibreSSL never sends a pre-shared key to the server and never aborts the handshake for lack of a pre-shared key. With OpenSSL, a client application wishing to use TLSv1.3 pre-shared keys can install a callback function cb using SSL_set_psk_use_session_callback(). The OpenSSL library may call cb once or twice during session negotiation. If the callback fails, OpenSSL aborts connection setup. If the callback succeeds but sets the *session pointer to NULL, OpenSSL continues the handshake but does not send a pre- shared key to the server. RETURN VALUES The SSL_psk_use_session_cb_func() callback is expected to return 1 on success or 0 on failure. HISTORY SSL_set_psk_use_session_callback() and SSL_psk_use_session_cb_func() first appeared in OpenSSL 1.1.1 and have been available since OpenBSD 7.0. FreeBSD 14.1-RELEASE-p8 September 14, 2021 FreeBSD 14.1-RELEASE-p8