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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" SSL_set1_host, SSL_add1_host, SSL_set_hostflags, SSL_get0_peername \- SSL server verification parameters .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #include <openssl/ssl.h> \& \& int SSL_set1_host(SSL *s, const char *hostname); \& int SSL_add1_host(SSL *s, const char *hostname); \& void SSL_set_hostflags(SSL *s, unsigned int flags); \& const char *SSL_get0_peername(SSL *s); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" These functions configure server hostname checks in the \s-1SSL\s0 client. .PP \&\fBSSL_set1_host()\fR sets the expected \s-1DNS\s0 hostname to \fBname\fR clearing any previously specified hostname or names. If \fBname\fR is \s-1NULL,\s0 or the empty string the list of hostnames is cleared, and name checks are not performed on the peer certificate. When a nonempty \&\fBname\fR is specified, certificate verification automatically checks the peer hostname via \fBX509_check_host\fR\|(3) with \fBflags\fR as specified via \fBSSL_set_hostflags()\fR. Clients that enable \s-1DANE TLSA\s0 authentication via \fBSSL_dane_enable\fR\|(3) should leave it to that function to set the primary reference identifier of the peer, and should not call \&\fBSSL_set1_host()\fR. .PP \&\fBSSL_add1_host()\fR adds \fBname\fR as an additional reference identifier that can match the peer's certificate. Any previous names set via \&\fBSSL_set1_host()\fR or \fBSSL_add1_host()\fR are retained, no change is made if \fBname\fR is \s-1NULL\s0 or empty. When multiple names are configured, the peer is considered verified when any name matches. This function is required for \s-1DANE TLSA\s0 in the presence of service name indirection via \s-1CNAME, MX\s0 or \s-1SRV\s0 records as specified in \s-1RFC7671, RFC7672\s0 or \&\s-1RFC7673.\s0 .PP \&\fBSSL_set_hostflags()\fR sets the \fBflags\fR that will be passed to \&\fBX509_check_host\fR\|(3) when name checks are applicable, by default the \fBflags\fR value is 0. See \fBX509_check_host\fR\|(3) for the list of available flags and their meaning. .PP \&\fBSSL_get0_peername()\fR returns the \s-1DNS\s0 hostname or subject CommonName from the peer certificate that matched one of the reference identifiers. When wildcard matching is not disabled, the name matched in the peer certificate may be a wildcard name. When one of the reference identifiers configured via \fBSSL_set1_host()\fR or \&\fBSSL_add1_host()\fR starts with \*(L".\*(R", which indicates a parent domain prefix rather than a fixed name, the matched peer name may be a sub-domain of the reference identifier. The returned string is allocated by the library and is no longer valid once the associated \fBssl\fR handle is cleared or freed, or a renegotiation takes place. Applications must not free the return value. .PP \&\s-1SSL\s0 clients are advised to use these functions in preference to explicitly calling \fBX509_check_host\fR\|(3). Hostname checks may be out of scope with the \s-1RFC7671 \fBDANE\-EE\s0\fR\|(3) certificate usage, and the internal check will be suppressed as appropriate when \s-1DANE\s0 is enabled. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fBSSL_set1_host()\fR and \fBSSL_add1_host()\fR return 1 for success and 0 for failure. .PP \&\fBSSL_get0_peername()\fR returns \s-1NULL\s0 if peername verification is not applicable (as with \s-1RFC7671 \fBDANE\-EE\s0\fR\|(3)), or no trusted peername was matched. Otherwise, it returns the matched peername. To determine whether verification succeeded call \fBSSL_get_verify_result\fR\|(3). .SH "EXAMPLES" .IX Header "EXAMPLES" Suppose \*(L"smtp.example.com\*(R" is the \s-1MX\s0 host of the domain \*(L"example.com\*(R". The calls below will arrange to match either the \s-1MX\s0 hostname or the destination domain name in the \s-1SMTP\s0 server certificate. Wildcards are supported, but must match the entire label. The actual name matched in the certificate (which might be a wildcard) is retrieved, and must be copied by the application if it is to be retained beyond the lifetime of the \s-1SSL\s0 connection. .PP .Vb 5 \& SSL_set_hostflags(ssl, X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS); \& if (!SSL_set1_host(ssl, "smtp.example.com")) \& /* error */ \& if (!SSL_add1_host(ssl, "example.com")) \& /* error */ \& \& /* XXX: Perform SSL_connect() handshake and handle errors here */ \& \& if (SSL_get_verify_result(ssl) == X509_V_OK) { \& const char *peername = SSL_get0_peername(ssl); \& \& if (peername != NULL) \& /* Name checks were in scope and matched the peername */ \& } .Ve .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBX509_check_host\fR\|(3), \&\fBSSL_get_verify_result\fR\|(3). \&\fBSSL_dane_enable\fR\|(3). .SH "HISTORY" .IX Header "HISTORY" These functions were added in OpenSSL 1.1.0. .SH "COPYRIGHT" .IX Header "COPYRIGHT" Copyright 2016\-2020 The OpenSSL Project Authors. All Rights Reserved. .PP Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.