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.\" ========================================================================
.\"
.IX Title "SSL_CTX_new 3"
.TH SSL_CTX_new 3 "2014-10-15" "1.0.1j" "OpenSSL"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
SSL_CTX_new \- create a new SSL_CTX object as framework for TLS/SSL enabled functions
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/ssl.h>
\&
\& SSL_CTX *SSL_CTX_new(const SSL_METHOD *method);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fISSL_CTX_new()\fR creates a new \fB\s-1SSL_CTX\s0\fR object as framework to establish
\&\s-1TLS/SSL\s0 enabled connections.
.SH "NOTES"
.IX Header "NOTES"
The \s-1SSL_CTX\s0 object uses \fBmethod\fR as connection method. The methods exist
in a generic type (for client and server use), a server only type, and a
client only type. \fBmethod\fR can be of the following types:
.IP "SSLv2_method(void), SSLv2_server_method(void), SSLv2_client_method(void)" 4
.IX Item "SSLv2_method(void), SSLv2_server_method(void), SSLv2_client_method(void)"
A \s-1TLS/SSL\s0 connection established with these methods will only understand
the SSLv2 protocol. A client will send out SSLv2 client hello messages
and will also indicate that it only understand SSLv2. A server will only
understand SSLv2 client hello messages.
.IP "SSLv3_method(void), SSLv3_server_method(void), SSLv3_client_method(void)" 4
.IX Item "SSLv3_method(void), SSLv3_server_method(void), SSLv3_client_method(void)"
A \s-1TLS/SSL\s0 connection established with these methods will only understand the
SSLv3 protocol. A client will send out SSLv3 client hello messages
and will indicate that it only understands SSLv3. A server will only understand
SSLv3 client hello messages. This especially means, that it will
not understand SSLv2 client hello messages which are widely used for
compatibility reasons, see SSLv23_*\fI_method()\fR.
.IP "TLSv1_method(void), TLSv1_server_method(void), TLSv1_client_method(void)" 4
.IX Item "TLSv1_method(void), TLSv1_server_method(void), TLSv1_client_method(void)"
A \s-1TLS/SSL\s0 connection established with these methods will only understand the
TLSv1 protocol. A client will send out TLSv1 client hello messages
and will indicate that it only understands TLSv1. A server will only understand
TLSv1 client hello messages. This especially means, that it will
not understand SSLv2 client hello messages which are widely used for
compatibility reasons, see SSLv23_*\fI_method()\fR. It will also not understand
SSLv3 client hello messages.
.IP "SSLv23_method(void), SSLv23_server_method(void), SSLv23_client_method(void)" 4
.IX Item "SSLv23_method(void), SSLv23_server_method(void), SSLv23_client_method(void)"
A \s-1TLS/SSL\s0 connection established with these methods may understand the SSLv2,
SSLv3, TLSv1, TLSv1.1 and TLSv1.2 protocols.
.Sp
If the cipher list does not contain any SSLv2 ciphersuites (the default
cipher list does not) or extensions are required (for example server name)
a client will send out TLSv1 client hello messages including extensions and
will indicate that it also understands TLSv1.1, TLSv1.2 and permits a
fallback to SSLv3. A server will support SSLv3, TLSv1, TLSv1.1 and TLSv1.2
protocols. This is the best choice when compatibility is a concern.
.Sp
If any SSLv2 ciphersuites are included in the cipher list and no extensions
are required then SSLv2 compatible client hellos will be used by clients and
SSLv2 will be accepted by servers. This is \fBnot\fR recommended due to the
insecurity of SSLv2 and the limited nature of the SSLv2 client hello
prohibiting the use of extensions.
.PP
The list of protocols available can later be limited using the SSL_OP_NO_SSLv2,
SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1 and SSL_OP_NO_TLSv1_2
options of the \fISSL_CTX_set_options()\fR or \fISSL_set_options()\fR functions.
Using these options it is possible to choose e.g. \fISSLv23_server_method()\fR and
be able to negotiate with all possible clients, but to only allow newer
protocols like TLSv1, TLSv1.1 or \s-1TLS\s0 v1.2.
.PP
Applications which never want to support SSLv2 (even is the cipher string
is configured to use SSLv2 ciphersuites) can set SSL_OP_NO_SSLv2.
.PP
\&\fISSL_CTX_new()\fR initializes the list of ciphers, the session cache setting,
the callbacks, the keys and certificates and the options to its default
values.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
The following return values can occur:
.IP "\s-1NULL\s0" 4
.IX Item "NULL"
The creation of a new \s-1SSL_CTX\s0 object failed. Check the error stack to
find out the reason.
.IP "Pointer to an \s-1SSL_CTX\s0 object" 4
.IX Item "Pointer to an SSL_CTX object"
The return value points to an allocated \s-1SSL_CTX\s0 object.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fISSL_CTX_free\fR\|(3), \fISSL_accept\fR\|(3),
\&\fIssl\fR\|(3), \fISSL_set_connect_state\fR\|(3)
|
