528b1f9a9f
Update protocols supported and note that SSLv2 is effectively disabled by default. PR#3184
119 lines
4.9 KiB
Text
119 lines
4.9 KiB
Text
=pod
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=head1 NAME
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SSL_CTX_new, SSLv2_method, SSLv2_server_method, SSLv2_client_method, SSLv3_method, SSLv3_server_method, SSLv3_client_method, TLSv1_method(void), TLSv1_server_method(void), TLSv1_client_method, TLSv1_1_method, TLSv1_1_server_method, TLSv1_1_client_method, SSLv23_method, SSLv23_server_method, SSLv23_client_method - create a new SSL_CTX object as framework for TLS/SSL enabled functions
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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SSL_CTX *SSL_CTX_new(const SSL_METHOD *method);
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=head1 DESCRIPTION
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SSL_CTX_new() creates a new B<SSL_CTX> object as framework to establish
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TLS/SSL enabled connections.
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=head1 NOTES
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The SSL_CTX object uses B<method> 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. B<method> can be of the following types:
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=over 4
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=item SSLv2_method(void), SSLv2_server_method(void), SSLv2_client_method(void)
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A TLS/SSL 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. The SSLv2 protocol is deprecated
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and very broken: its use is B<strongly> discouraged.
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=item SSLv3_method(void), SSLv3_server_method(void), SSLv3_client_method(void)
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A TLS/SSL 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_*_method().
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=item TLSv1_method(void), TLSv1_server_method(void), TLSv1_client_method(void)
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A TLS/SSL 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_*_method(). It will also not understand
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SSLv3 client hello messages.
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=item TLSv1_1_method(void), TLSv1_1_server_method(void), TLSv1_1_client_method(void)
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A TLS/SSL connection established with these methods will only understand the
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TLSv1.1 protocol. A client will send out TLSv1.1 client hello messages
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and will indicate that it only understands TLSv1.1. A server will only
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understand TLSv1.1 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_*_method(). It will also not understand
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SSLv3 client hello messages.
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=item SSLv23_method(void), SSLv23_server_method(void), SSLv23_client_method(void)
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A TLS/SSL 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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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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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 B<not> 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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=back
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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 SSL_CTX_set_options() or SSL_set_options() functions.
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Using these options it is possible to choose e.g. SSLv23_server_method() 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 TLS v1.2.
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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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SSL_CTX_new() 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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=head1 RETURN VALUES
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The following return values can occur:
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=over 4
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=item NULL
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The creation of a new SSL_CTX object failed. Check the error stack to
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find out the reason.
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=item Pointer to an SSL_CTX object
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The return value points to an allocated SSL_CTX object.
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=back
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=head1 SEE ALSO
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L<SSL_CTX_free(3)|SSL_CTX_free(3)>, L<SSL_accept(3)|SSL_accept(3)>,
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L<ssl(3)|ssl(3)>, L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>
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=cut
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