227 lines
8.4 KiB
Groff
227 lines
8.4 KiB
Groff
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.\" ========================================================================
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.\"
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.IX Title "SSL_CTX_new 3"
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.TH SSL_CTX_new 3 "2015-06-11" "1.0.1n" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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SSL_CTX_new \- create a new SSL_CTX object as framework for TLS/SSL enabled functions
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/ssl.h>
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\&
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\& SSL_CTX *SSL_CTX_new(const SSL_METHOD *method);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fISSL_CTX_new()\fR creates a new \fB\s-1SSL_CTX\s0\fR object as framework to establish
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\&\s-1TLS/SSL\s0 enabled connections.
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.SH "NOTES"
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.IX Header "NOTES"
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The \s-1SSL_CTX\s0 object uses \fBmethod\fR as connection method. The methods exist
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in a generic type (for client and server use), a server only type, and a
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client only type. \fBmethod\fR can be of the following types:
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.IP "SSLv2_method(void), SSLv2_server_method(void), SSLv2_client_method(void)" 4
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.IX Item "SSLv2_method(void), SSLv2_server_method(void), SSLv2_client_method(void)"
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A \s-1TLS/SSL\s0 connection established with these methods will only understand
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the SSLv2 protocol. A client will send out SSLv2 client hello messages
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and will also indicate that it only understand SSLv2. A server will only
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understand SSLv2 client hello messages.
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.IP "SSLv3_method(void), SSLv3_server_method(void), SSLv3_client_method(void)" 4
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.IX Item "SSLv3_method(void), SSLv3_server_method(void), SSLv3_client_method(void)"
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A \s-1TLS/SSL\s0 connection established with these methods will only understand the
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SSLv3 protocol. A client will send out SSLv3 client hello messages
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and will indicate that it only understands SSLv3. A server will only understand
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SSLv3 client hello messages. This especially means, that it will
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not understand SSLv2 client hello messages which are widely used for
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compatibility reasons, see SSLv23_*\fI_method()\fR.
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.IP "TLSv1_method(void), TLSv1_server_method(void), TLSv1_client_method(void)" 4
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.IX Item "TLSv1_method(void), TLSv1_server_method(void), TLSv1_client_method(void)"
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A \s-1TLS/SSL\s0 connection established with these methods will only understand the
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TLSv1 protocol. A client will send out TLSv1 client hello messages
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and will indicate that it only understands TLSv1. A server will only understand
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TLSv1 client hello messages. This especially means, that it will
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not understand SSLv2 client hello messages which are widely used for
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compatibility reasons, see SSLv23_*\fI_method()\fR. It will also not understand
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SSLv3 client hello messages.
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.IP "SSLv23_method(void), SSLv23_server_method(void), SSLv23_client_method(void)" 4
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.IX Item "SSLv23_method(void), SSLv23_server_method(void), SSLv23_client_method(void)"
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A \s-1TLS/SSL\s0 connection established with these methods may understand the SSLv2,
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SSLv3, TLSv1, TLSv1.1 and TLSv1.2 protocols.
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.Sp
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If the cipher list does not contain any SSLv2 ciphersuites (the default
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cipher list does not) or extensions are required (for example server name)
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a client will send out TLSv1 client hello messages including extensions and
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will indicate that it also understands TLSv1.1, TLSv1.2 and permits a
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fallback to SSLv3. A server will support SSLv3, TLSv1, TLSv1.1 and TLSv1.2
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protocols. This is the best choice when compatibility is a concern.
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.Sp
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If any SSLv2 ciphersuites are included in the cipher list and no extensions
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are required then SSLv2 compatible client hellos will be used by clients and
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SSLv2 will be accepted by servers. This is \fBnot\fR recommended due to the
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insecurity of SSLv2 and the limited nature of the SSLv2 client hello
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prohibiting the use of extensions.
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.PP
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The list of protocols available can later be limited using the SSL_OP_NO_SSLv2,
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SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1 and SSL_OP_NO_TLSv1_2
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options of the \fISSL_CTX_set_options()\fR or \fISSL_set_options()\fR functions.
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Using these options it is possible to choose e.g. \fISSLv23_server_method()\fR and
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be able to negotiate with all possible clients, but to only allow newer
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protocols like TLSv1, TLSv1.1 or \s-1TLS\s0 v1.2.
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.PP
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Applications which never want to support SSLv2 (even is the cipher string
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is configured to use SSLv2 ciphersuites) can set SSL_OP_NO_SSLv2.
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.PP
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\&\fISSL_CTX_new()\fR initializes the list of ciphers, the session cache setting,
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the callbacks, the keys and certificates and the options to its default
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values.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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The following return values can occur:
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.IP "\s-1NULL\s0" 4
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.IX Item "NULL"
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The creation of a new \s-1SSL_CTX\s0 object failed. Check the error stack to
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find out the reason.
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.IP "Pointer to an \s-1SSL_CTX\s0 object" 4
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.IX Item "Pointer to an SSL_CTX object"
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The return value points to an allocated \s-1SSL_CTX\s0 object.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fISSL_CTX_free\fR\|(3), \fISSL_accept\fR\|(3),
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\&\fIssl\fR\|(3), \fISSL_set_connect_state\fR\|(3)
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