SSL: logging level of "no suitable key share". The "no suitable key share" errors are reported by OpenSSL 1.1.1 when using TLSv1.3 if there are no shared groups (that is, elliptic curves). In particular, it is easy enough to trigger by using only a single curve in ssl_ecdh_curve: ssl_ecdh_curve secp384r1; and using a different curve in the client: openssl s_client -connect 127.0.0.1:443 -curves prime256v1 On the client side it is seen as "sslv3 alert handshake failure", "SSL alert number 40": 0:error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert handshake failure:ssl/record/rec_layer_s3.c:1528:SSL alert number 40 It can be also triggered with default ssl_ecdh_curve by using a curve which is not in the default list (X25519, prime256v1, X448, secp521r1, secp384r1): openssl s_client -connect 127.0.0.1:8443 -curves brainpoolP512r1 Given that many clients hardcode prime256v1, these errors might become a common problem with TLSv1.3 if ssl_ecdh_curve is redefined. Previously this resulted in not using ECDH with such clients, but with TLSv1.3 it is no longer possible and will result in a handshake failure. The SSL_R_NO_SHARED_GROUP error is what BoringSSL returns in the same situation. Seen at: https://serverfault.com/questions/932102/nginx-ssl-handshake-error-no-suitable-key-share

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#ifndef _NGX_MAIL_SSL_H_INCLUDED_
#define _NGX_MAIL_SSL_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_mail.h>


#define NGX_MAIL_STARTTLS_OFF   0
#define NGX_MAIL_STARTTLS_ON    1
#define NGX_MAIL_STARTTLS_ONLY  2


typedef struct {
    ngx_flag_t       enable;
    ngx_flag_t       prefer_server_ciphers;

    ngx_ssl_t        ssl;

    ngx_uint_t       starttls;
    ngx_uint_t       listen;
    ngx_uint_t       protocols;

    ngx_uint_t       verify;
    ngx_uint_t       verify_depth;

    ssize_t          builtin_session_cache;

    time_t           session_timeout;

    ngx_array_t     *certificates;
    ngx_array_t     *certificate_keys;

    ngx_str_t        dhparam;
    ngx_str_t        ecdh_curve;
    ngx_str_t        client_certificate;
    ngx_str_t        trusted_certificate;
    ngx_str_t        crl;

    ngx_str_t        ciphers;

    ngx_array_t     *passwords;

    ngx_shm_zone_t  *shm_zone;

    ngx_flag_t       session_tickets;
    ngx_array_t     *session_ticket_keys;

    u_char          *file;
    ngx_uint_t       line;
} ngx_mail_ssl_conf_t;


extern ngx_module_t  ngx_mail_ssl_module;


#endif /* _NGX_MAIL_SSL_H_INCLUDED_ */