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authorbeck <beck@openbsd.org>2016-09-03 11:33:34 +0000
committerbeck <beck@openbsd.org>2016-09-03 11:33:34 +0000
commit8204a9859e29f943f9d45fa3c5bacf005da87a21 (patch)
tree3d72799b17122728ed1ce817d171df956c52a633 /lib/libssl/src/doc/ssl/SSL_CTX_set_options.3
parentRemove NULL pointer checks before calls to free(). (diff)
downloadwireguard-openbsd-8204a9859e29f943f9d45fa3c5bacf005da87a21.tar.xz
wireguard-openbsd-8204a9859e29f943f9d45fa3c5bacf005da87a21.zip
Remove the libssl/src directory
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-.\"
-.\" $OpenBSD: SSL_CTX_set_options.3,v 1.10 2015/07/18 19:41:54 doug Exp $
-.\"
-.Dd $Mdocdate: July 18 2015 $
-.Dt SSL_CTX_SET_OPTIONS 3
-.Os
-.Sh NAME
-.Nm SSL_CTX_set_options ,
-.Nm SSL_set_options ,
-.Nm SSL_CTX_clear_options ,
-.Nm SSL_clear_options ,
-.Nm SSL_CTX_get_options ,
-.Nm SSL_get_options ,
-.Nm SSL_get_secure_renegotiation_support
-.Nd manipulate SSL options
-.Sh SYNOPSIS
-.In openssl/ssl.h
-.Ft long
-.Fn SSL_CTX_set_options "SSL_CTX *ctx" "long options"
-.Ft long
-.Fn SSL_set_options "SSL *ssl" "long options"
-.Ft long
-.Fn SSL_CTX_clear_options "SSL_CTX *ctx" "long options"
-.Ft long
-.Fn SSL_clear_options "SSL *ssl" "long options"
-.Ft long
-.Fn SSL_CTX_get_options "SSL_CTX *ctx"
-.Ft long
-.Fn SSL_get_options "SSL *ssl"
-.Ft long
-.Fn SSL_get_secure_renegotiation_support "SSL *ssl"
-.Sh DESCRIPTION
-Note: all these functions are implemented using macros.
-.Pp
-.Fn SSL_CTX_set_options
-adds the options set via bitmask in
-.Fa options
-to
-.Fa ctx .
-Options already set before are not cleared!
-.Pp
-.Fn SSL_set_options
-adds the options set via bitmask in
-.Fa options
-to
-.Fa ssl .
-Options already set before are not cleared!
-.Pp
-.Fn SSL_CTX_clear_options
-clears the options set via bitmask in
-.Fa options
-to
-.Fa ctx .
-.Pp
-.Fn SSL_clear_options
-clears the options set via bitmask in
-.Fa options
-to
-.Fa ssl .
-.Pp
-.Fn SSL_CTX_get_options
-returns the options set for
-.Fa ctx .
-.Pp
-.Fn SSL_get_options
-returns the options set for
-.Fa ssl .
-.Pp
-.Fn SSL_get_secure_renegotiation_support
-indicates whether the peer supports secure renegotiation.
-.Sh NOTES
-The behaviour of the SSL library can be changed by setting several options.
-The options are coded as bitmasks and can be combined by a bitwise OR
-operation (|).
-.Pp
-.Fn SSL_CTX_set_options
-and
-.Fn SSL_set_options
-affect the (external) protocol behaviour of the SSL library.
-The (internal) behaviour of the API can be changed by using the similar
-.Xr SSL_CTX_set_mode 3
-and
-.Xr SSL_set_mode 3
-functions.
-.Pp
-During a handshake, the option settings of the SSL object are used.
-When a new SSL object is created from a context using
-.Xr SSL_new 3 ,
-the current option setting is copied.
-Changes to
-.Fa ctx
-do not affect already created
-.Vt SSL
-objects.
-.Fn SSL_clear
-does not affect the settings.
-.Pp
-The following
-.Em bug workaround
-options are available:
-.Bl -tag -width Ds
-.It Dv SSL_OP_MICROSOFT_SESS_ID_BUG
-As of
-.Ox 5.8 ,
-this option has no effect.
-.It Dv SSL_OP_NETSCAPE_CHALLENGE_BUG
-As of
-.Ox 5.8 ,
-this option has no effect.
-.It Dv SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
-As of OpenSSL 0.9.8q and 1.0.0c, this option has no effect.
-.It Dv SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
-As of
-.Ox 5.8 ,
-this option has no effect.
-.It Dv SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
-As of
-.Ox 5.8 ,
-this option has no effect.
-.It Dv SSL_OP_SAFARI_ECDHE_ECDSA_BUG
-As of
-.Ox 5.8 ,
-this option has no effect.
-.It Dv SSL_OP_SSLEAY_080_CLIENT_DH_BUG
-As of
-.Ox 5.8 ,
-this option has no effect.
-.It Dv SSL_OP_TLS_D5_BUG
-As of
-.Ox 5.8 ,
-this option has no effect.
-.It Dv SSL_OP_TLS_BLOCK_PADDING_BUG
-As of
-.Ox 5.8 ,
-this option has no effect.
-.It Dv SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
-Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol vulnerability
-affecting CBC ciphers, which cannot be handled by some broken SSL
-implementations.
-This option has no effect for connections using other ciphers.
-.It Dv SSL_OP_TLSEXT_PADDING
-Adds a padding extension to ensure the ClientHello size is never between 256
-and 511 bytes in length.
-This is needed as a workaround for some implementations.
-.It Dv SSL_OP_ALL
-All of the above bug workarounds.
-.El
-.Pp
-It is usually safe to use
-.Dv SSL_OP_ALL
-to enable the bug workaround options if compatibility with somewhat broken
-implementations is desired.
-.Pp
-The following
-.Em modifying
-options are available:
-.Bl -tag -width Ds
-.It Dv SSL_OP_TLS_ROLLBACK_BUG
-Disable version rollback attack detection.
-.Pp
-During the client key exchange, the client must send the same information
-about acceptable SSL/TLS protocol levels as during the first hello.
-Some clients violate this rule by adapting to the server's answer.
-(Example: the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1,
-the server only understands up to SSLv3.
-In this case the client must still use the same SSLv3.1=TLSv1 announcement.
-Some clients step down to SSLv3 with respect to the server's answer and violate
-the version rollback protection.)
-.It Dv SSL_OP_SINGLE_DH_USE
-Always create a new key when using temporary/ephemeral DH parameters
-(see
-.Xr SSL_CTX_set_tmp_dh_callback 3 ) .
-This option must be used to prevent small subgroup attacks, when the DH
-parameters were not generated using
-.Dq strong
-primes (e.g., when using DSA-parameters, see
-.Xr openssl 1 ) .
-If
-.Dq strong
-primes were used, it is not strictly necessary to generate a new DH key during
-each handshake but it is also recommended.
-.Dv SSL_OP_SINGLE_DH_USE
-should therefore be enabled whenever temporary/ephemeral DH parameters are used.
-.It SSL_OP_EPHEMERAL_RSA
-Always use ephemeral (temporary) RSA key when doing RSA operations (see
-.Xr SSL_CTX_set_tmp_rsa_callback 3 ) .
-According to the specifications, this is only done when a RSA key can only be
-used for signature operations (namely under export ciphers with restricted RSA
-keylength).
-By setting this option, ephemeral RSA keys are always used.
-This option breaks compatibility with the SSL/TLS specifications and may lead
-to interoperability problems with clients and should therefore never be used.
-Ciphers with EDH (ephemeral Diffie-Hellman) key exchange should be used instead.
-.It Dv SSL_OP_CIPHER_SERVER_PREFERENCE
-When choosing a cipher, use the server's preferences instead of the client
-preferences.
-When not set, the SSL server will always follow the client's preferences.
-When set, the SSLv3/TLSv1 server will choose following its own preferences.
-Because of the different protocol, for SSLv2 the server will send its list of
-preferences to the client and the client chooses.
-.It Dv SSL_OP_NETSCAPE_CA_DN_BUG
-As of
-.Ox 5.8 ,
-this option has no effect.
-.It Dv SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
-As of
-.Ox 5.8 ,
-this option has no effect.
-.It Dv SSL_OP_NO_SSLv2
-As of
-.Ox 5.6 ,
-this option has no effect as SSLv2 support has been removed.
-In previous versions it disabled use of the SSLv2 protocol.
-.It Dv SSL_OP_NO_SSLv3
-Do not use the SSLv3 protocol.
-.It Dv SSL_OP_NO_TLSv1
-Do not use the TLSv1.0 protocol.
-.It Dv SSL_OP_NO_TLSv1_1
-Do not use the TLSv1.1 protocol.
-.It Dv SSL_OP_NO_TLSv1_2
-Do not use the TLSv1.2 protocol.
-.It Dv SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
-When performing renegotiation as a server, always start a new session (i.e.,
-session resumption requests are only accepted in the initial handshake).
-This option is not needed for clients.
-.It Dv SSL_OP_NO_TICKET
-Normally clients and servers will, where possible, transparently make use of
-RFC4507bis tickets for stateless session resumption.
-.Pp
-If this option is set this functionality is disabled and tickets will not be
-used by clients or servers.
-.It Dv SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
-As of
-.Ox 5.6 ,
-this option has no effect.
-In previous versions it allowed legacy insecure renegotiation between OpenSSL
-and unpatched clients or servers.
-See the
-.Sx SECURE RENEGOTIATION
-section for more details.
-.It Dv SSL_OP_LEGACY_SERVER_CONNECT
-Allow legacy insecure renegotiation between OpenSSL and unpatched servers
-.Em only :
-this option is currently set by default.
-See the
-.Sx SECURE RENEGOTIATION
-section for more details.
-.El
-.Sh SECURE RENEGOTIATION
-OpenSSL 0.9.8m and later always attempts to use secure renegotiation as
-described in RFC5746.
-This counters the prefix attack described in CVE-2009-3555 and elsewhere.
-.Pp
-The deprecated and highly broken SSLv2 protocol does not support renegotiation
-at all; its use is
-.Em strongly
-discouraged.
-.Pp
-This attack has far-reaching consequences which application writers should be
-aware of.
-In the description below an implementation supporting secure renegotiation is
-referred to as
-.Dq patched .
-A server not supporting secure
-renegotiation is referred to as
-.Dq unpatched .
-.Pp
-The following sections describe the operations permitted by OpenSSL's secure
-renegotiation implementation.
-.Ss Patched client and server
-Connections and renegotiation are always permitted by OpenSSL implementations.
-.Ss Unpatched client and patched OpenSSL server
-The initial connection succeeds but client renegotiation is denied by the
-server with a
-.Em no_renegotiation
-warning alert if TLS v1.0 is used or a fatal
-.Em handshake_failure
-alert in SSL v3.0.
-.Pp
-If the patched OpenSSL server attempts to renegotiate a fatal
-.Em handshake_failure
-alert is sent.
-This is because the server code may be unaware of the unpatched nature of the
-client.
-.Pp
-.Em N.B.:
-a bug in OpenSSL clients earlier than 0.9.8m (all of which are unpatched) will
-result in the connection hanging if it receives a
-.Em no_renegotiation
-alert.
-OpenSSL versions 0.9.8m and later will regard a
-.Em no_renegotiation
-alert as fatal and respond with a fatal
-.Em handshake_failure
-alert.
-This is because the OpenSSL API currently has no provision to indicate to an
-application that a renegotiation attempt was refused.
-.Ss Patched OpenSSL client and unpatched server
-If the option
-.Dv SSL_OP_LEGACY_SERVER_CONNECT
-is set then initial connections and renegotiation between patched OpenSSL
-clients and unpatched servers succeeds.
-If neither option is set then initial connections to unpatched servers will
-fail.
-.Pp
-The option
-.Dv SSL_OP_LEGACY_SERVER_CONNECT
-is currently set by default even though it has security implications:
-otherwise it would be impossible to connect to unpatched servers (i.e., all of
-them initially) and this is clearly not acceptable.
-Renegotiation is permitted because this does not add any additional security
-issues: during an attack clients do not see any renegotiations anyway.
-.Pp
-As more servers become patched the option
-.Dv SSL_OP_LEGACY_SERVER_CONNECT
-will
-.Em not
-be set by default in a future version of OpenSSL.
-.Pp
-OpenSSL client applications wishing to ensure they can connect to unpatched
-servers should always
-.Em set
-.Dv SSL_OP_LEGACY_SERVER_CONNECT
-.Pp
-OpenSSL client applications that want to ensure they can
-.Em not
-connect to unpatched servers (and thus avoid any security issues) should always
-.Em clear
-.Dv SSL_OP_LEGACY_SERVER_CONNECT
-using
-.Fn SSL_CTX_clear_options
-or
-.Fn SSL_clear_options .
-.Sh RETURN VALUES
-.Fn SSL_CTX_set_options
-and
-.Fn SSL_set_options
-return the new options bitmask after adding
-.Fa options .
-.Pp
-.Fn SSL_CTX_clear_options
-and
-.Fn SSL_clear_options
-return the new options bitmask after clearing
-.Fa options .
-.Pp
-.Fn SSL_CTX_get_options
-and
-.Fn SSL_get_options
-return the current bitmask.
-.Pp
-.Fn SSL_get_secure_renegotiation_support
-returns 1 is the peer supports secure renegotiation and 0 if it does not.
-.Sh SEE ALSO
-.Xr openssl 1 ,
-.Xr ssl 3 ,
-.Xr SSL_clear 3 ,
-.Xr SSL_CTX_set_tmp_dh_callback 3 ,
-.Xr SSL_CTX_set_tmp_rsa_callback 3 ,
-.Xr SSL_new 3
-.Sh HISTORY
-.Dv SSL_OP_CIPHER_SERVER_PREFERENCE
-and
-.Dv SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
-have been added in
-OpenSSL 0.9.7.
-.Pp
-.Dv SSL_OP_TLS_ROLLBACK_BUG
-has been added in OpenSSL 0.9.6 and was automatically enabled with
-.Dv SSL_OP_ALL .
-As of 0.9.7, it is no longer included in
-.Dv SSL_OP_ALL
-and must be explicitly set.
-.Pp
-.Dv SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
-has been added in OpenSSL 0.9.6e.
-Versions up to OpenSSL 0.9.6c do not include the countermeasure that can be
-disabled with this option (in OpenSSL 0.9.6d, it was always enabled).
-.Pp
-.Fn SSL_CTX_clear_options
-and
-.Fn SSL_clear_options
-were first added in OpenSSL 0.9.8m.
-.Pp
-.Dv SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION ,
-.Dv SSL_OP_LEGACY_SERVER_CONNECT
-and the function
-.Fn SSL_get_secure_renegotiation_support
-were first added in OpenSSL 0.9.8m.
-.Pp
-.Dv SSL_OP_NO_SSLv2
-and
-.Dv SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
-were changed to have no effect in
-.Ox 5.6 .