235 lines
7.5 KiB
Text
235 lines
7.5 KiB
Text
=pod
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=head1 NAME
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SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options, SSL_get_options - manipulate SSL engine options
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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long SSL_CTX_set_options(SSL_CTX *ctx, long options);
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long SSL_set_options(SSL *ssl, long options);
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long SSL_CTX_get_options(SSL_CTX *ctx);
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long SSL_get_options(SSL *ssl);
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=head1 DESCRIPTION
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SSL_CTX_set_options() adds the options set via bitmask in B<options> to B<ctx>.
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Options already set before are not cleared!
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SSL_set_options() adds the options set via bitmask in B<options> to B<ssl>.
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Options already set before are not cleared!
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SSL_CTX_get_options() returns the options set for B<ctx>.
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SSL_get_options() returns the options set for B<ssl>.
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=head1 NOTES
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The behaviour of the SSL library can be changed by setting several options.
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The options are coded as bitmasks and can be combined by a logical B<or>
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operation (|). Options can only be added but can never be reset.
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SSL_CTX_set_options() and SSL_set_options() affect the (external)
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protocol behaviour of the SSL library. The (internal) behaviour of
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the API can be changed by using the similar
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L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> and SSL_set_mode() functions.
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During a handshake, the option settings of the SSL object are used. When
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a new SSL object is created from a context using SSL_new(), the current
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option setting is copied. Changes to B<ctx> do not affect already created
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SSL objects. SSL_clear() does not affect the settings.
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The following B<bug workaround> options are available:
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=over 4
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=item SSL_OP_MICROSOFT_SESS_ID_BUG
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www.microsoft.com - when talking SSLv2, if session-id reuse is
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performed, the session-id passed back in the server-finished message
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is different from the one decided upon.
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=item SSL_OP_NETSCAPE_CHALLENGE_BUG
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Netscape-Commerce/1.12, when talking SSLv2, accepts a 32 byte
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challenge but then appears to only use 16 bytes when generating the
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encryption keys. Using 16 bytes is ok but it should be ok to use 32.
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According to the SSLv3 spec, one should use 32 bytes for the challenge
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when operating in SSLv2/v3 compatibility mode, but as mentioned above,
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this breaks this server so 16 bytes is the way to go.
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=item SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
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ssl3.netscape.com:443, first a connection is established with RC4-MD5.
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If it is then resumed, we end up using DES-CBC3-SHA. It should be
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RC4-MD5 according to 7.6.1.3, 'cipher_suite'.
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Netscape-Enterprise/2.01 (https://merchant.netscape.com) has this bug.
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It only really shows up when connecting via SSLv2/v3 then reconnecting
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via SSLv3. The cipher list changes....
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NEW INFORMATION. Try connecting with a cipher list of just
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DES-CBC-SHA:RC4-MD5. For some weird reason, each new connection uses
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RC4-MD5, but a re-connect tries to use DES-CBC-SHA. So netscape, when
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doing a re-connect, always takes the first cipher in the cipher list.
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=item SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
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...
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=item SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
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...
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=item SSL_OP_MSIE_SSLV2_RSA_PADDING
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...
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=item SSL_OP_SSLEAY_080_CLIENT_DH_BUG
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...
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=item SSL_OP_TLS_D5_BUG
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...
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=item SSL_OP_TLS_BLOCK_PADDING_BUG
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...
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=item SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
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Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol
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vulnerability affecting CBC ciphers, which cannot be handled by some
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broken SSL implementations. This option has no effect for connections
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using other ciphers.
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=item SSL_OP_ALL
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All of the above bug workarounds.
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=back
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It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround
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options if compatibility with somewhat broken implementations is
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desired.
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The following B<modifying> options are available:
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=over 4
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=item SSL_OP_TLS_ROLLBACK_BUG
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Disable version rollback attack detection.
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During the client key exchange, the client must send the same information
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about acceptable SSL/TLS protocol levels as during the first hello. Some
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clients violate this rule by adapting to the server's answer. (Example:
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the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
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only understands up to SSLv3. In this case the client must still use the
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same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
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to the server's answer and violate the version rollback protection.)
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=item SSL_OP_SINGLE_DH_USE
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Always create a new key when using temporary/ephemeral DH parameters
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(see L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>).
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This option must be used to prevent small subgroup attacks, when
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the DH parameters were not generated using "strong" primes
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(e.g. when using DSA-parameters, see L<dhparam(1)|dhparam(1)>).
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If "strong" primes were used, it is not strictly necessary to generate
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a new DH key during each handshake but it is also recommended.
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B<SSL_OP_SINGLE_DH_USE> should therefore be enabled whenever
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temporary/ephemeral DH parameters are used.
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=item SSL_OP_EPHEMERAL_RSA
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Always use ephemeral (temporary) RSA key when doing RSA operations
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(see L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>).
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According to the specifications this is only done, when a RSA key
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can only be used for signature operations (namely under export ciphers
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with restricted RSA keylength). By setting this option, ephemeral
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RSA keys are always used. This option breaks compatibility with the
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SSL/TLS specifications and may lead to interoperability problems with
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clients and should therefore never be used. Ciphers with EDH (ephemeral
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Diffie-Hellman) key exchange should be used instead.
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=item SSL_OP_CIPHER_SERVER_PREFERENCE
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When choosing a cipher, use the server's preferences instead of the client
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preferences. When not set, the SSL server will always follow the clients
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preferences. When set, the SSLv3/TLSv1 server will choose following its
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own preferences. Because of the different protocol, for SSLv2 the server
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will send his list of preferences to the client and the client chooses.
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=item SSL_OP_PKCS1_CHECK_1
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...
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=item SSL_OP_PKCS1_CHECK_2
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...
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=item SSL_OP_NETSCAPE_CA_DN_BUG
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If we accept a netscape connection, demand a client cert, have a
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non-self-signed CA which does not have its CA in netscape, and the
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browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta
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=item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
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...
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=item SSL_OP_NO_SSLv2
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Do not use the SSLv2 protocol.
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=item SSL_OP_NO_SSLv3
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Do not use the SSLv3 protocol.
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=item SSL_OP_NO_TLSv1
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Do not use the TLSv1 protocol.
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=item SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
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When performing renegotiation as a server, always start a new session
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(i.e., session resumption requests are only accepted in the initial
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handshake). This option is not needed for clients.
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=back
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=head1 RETURN VALUES
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SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
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after adding B<options>.
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SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
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=head1 SEE ALSO
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L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,
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L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
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L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
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L<dhparam(1)|dhparam(1)>
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=head1 HISTORY
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B<SSL_OP_CIPHER_SERVER_PREFERENCE> and
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B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in
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OpenSSL 0.9.7.
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B<SSL_OP_TLS_ROLLBACK_BUG> has been added in OpenSSL 0.9.6 and was automatically
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enabled with B<SSL_OP_ALL>. As of 0.9.7, it is no longer included in B<SSL_OP_ALL>
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and must be explicitly set.
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B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> has been added in OpenSSL 0.9.6e.
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Versions up to OpenSSL 0.9.6c do not include the countermeasure that
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can be disabled with this option (in OpenSSL 0.9.6d, it was always
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enabled).
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=cut
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