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Title "SSL_SET1_HOST 3" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
SSL_set1_host, SSL_add1_host, SSL_set_hostflags, SSL_get0_peername - SSL server verification parameters 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 Header "DESCRIPTION" These functions configure server hostname checks in the \s-1SSL\s0 client.

\fBSSL_set1_host() sets the expected \s-1DNS\s0 hostname to name clearing any previously specified hostname. If name 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 is specified, certificate verification automatically checks the peer hostname via X509_check_host\|(3) with flags as specified via SSL_set_hostflags(). Clients that enable \s-1DANE TLSA\s0 authentication via SSL_dane_enable\|(3) should leave it to that function to set the primary reference identifier of the peer, and should not call \fBSSL_set1_host().

\fBSSL_add1_host() adds name as an additional reference identifier that can match the peer's certificate. Any previous names set via \fBSSL_set1_host() or SSL_add1_host() are retained, no change is made if name 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

\fBSSL_set_hostflags() sets the flags that will be passed to \fBX509_check_host\|(3) when name checks are applicable, by default the flags value is 0. See X509_check_host\|(3) for the list of available flags and their meaning.

\fBSSL_get0_peername() 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 SSL_set1_host() or \fBSSL_add1_host() 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 ssl handle is cleared or freed, or a renegotiation takes place. Applications must not free the return value.

\s-1SSL\s0 clients are advised to use these functions in preference to explicitly calling X509_check_host\|(3). Hostname checks may be out of scope with the \s-1RFC7671 DANE-EE\s0\|(3) certificate usage, and the internal check will be suppressed as appropriate when \s-1DANE\s0 is enabled.

Header "RETURN VALUES" \fBSSL_set1_host() and SSL_add1_host() return 1 for success and 0 for failure.

\fBSSL_get0_peername() returns \s-1NULL\s0 if peername verification is not applicable (as with \s-1RFC7671 DANE-EE\s0\|(3)), or no trusted peername was matched. Otherwise, it returns the matched peername. To determine whether verification succeeded call SSL_get_verify_result\|(3).

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.

.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

Header "SEE ALSO" \fBssl\|(7), \fBX509_check_host\|(3), \fBSSL_get_verify_result\|(3). \fBSSL_dane_enable\|(3). Header "HISTORY" These functions were added in OpenSSL 1.1.0. Header "COPYRIGHT" Copyright 2016-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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>.