/usr/man/cat.3/SSL_set_options.3
SSL_CTX_set_options(3) OpenSSL SSL_CTX_set_options(3)
NAME
SSL_CTX_set_options, SSL_set_options, SSL_CTX_clear_options,
SSL_clear_options, SSL_CTX_get_options, SSL_get_options,
SSL_get_secure_renegotiation_support - manipulate SSL
options
SYNOPSIS
#include <openssl/ssl.h>
long SSL_CTX_set_options(SSL_CTX *ctx, long options);
long SSL_set_options(SSL *ssl, long options);
long SSL_CTX_clear_options(SSL_CTX *ctx, long options);
long SSL_clear_options(SSL *ssl, long options);
long SSL_CTX_get_options(SSL_CTX *ctx);
long SSL_get_options(SSL *ssl);
long SSL_get_secure_renegotiation_support(SSL *ssl);
DESCRIPTION
Note: all these functions are implemented using macros.
SSL_CTX_set_options() adds the options set via bitmask in
options to ctx. Options already set before are not cleared!
SSL_set_options() adds the options set via bitmask in
options to ssl. Options already set before are not cleared!
SSL_CTX_clear_options() clears the options set via bitmask
in options to ctx.
SSL_clear_options() clears the options set via bitmask in
options to ssl.
SSL_CTX_get_options() returns the options set for ctx.
SSL_get_options() returns the options set for ssl.
SSL_get_secure_renegotiation_support() indicates whether the
peer supports secure renegotiation.
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 logical or operation (|).
SSL_CTX_set_options() and 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 SSL_CTX_set_mode(3) and SSL_set_mode() functions.
1.0.2t Last change: 2019-09-10 1
SSL_CTX_set_options(3) OpenSSL SSL_CTX_set_options(3)
During a handshake, the option settings of the SSL object
are used. When a new SSL object is created from a context
using SSL_new(), the current option setting is copied.
Changes to ctx do not affect already created SSL objects.
SSL_clear() does not affect the settings.
The following bug workaround options are available:
SSL_OP_MICROSOFT_SESS_ID_BUG
www.microsoft.com - when talking SSLv2, if session-id
reuse is performed, the session-id passed back in the
server-finished message is different from the one
decided upon.
SSL_OP_NETSCAPE_CHALLENGE_BUG
Netscape-Commerce/1.12, when talking SSLv2, accepts a 32
byte challenge but then appears to only use 16 bytes
when generating the encryption keys. Using 16 bytes is
ok but it should be ok to use 32. According to the
SSLv3 spec, one should use 32 bytes for the challenge
when operating in SSLv2/v3 compatibility mode, but as
mentioned above, this breaks this server so 16 bytes is
the way to go.
SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
As of OpenSSL 0.9.8q and 1.0.0c, this option has no
effect.
SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
...
SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
...
SSL_OP_SAFARI_ECDHE_ECDSA_BUG
Don't prefer ECDHE-ECDSA ciphers when the client appears
to be Safari on OS X. OS X 10.8..10.8.3 has broken
support for ECDHE-ECDSA ciphers.
SSL_OP_SSLEAY_080_CLIENT_DH_BUG
...
SSL_OP_TLS_D5_BUG
...
SSL_OP_TLS_BLOCK_PADDING_BUG
...
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.
1.0.2t Last change: 2019-09-10 2
SSL_CTX_set_options(3) OpenSSL SSL_CTX_set_options(3)
This option has no effect for connections using other
ciphers.
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.
SSL_OP_ALL
All of the above bug workarounds.
It is usually safe to use SSL_OP_ALL to enable the bug
workaround options if compatibility with somewhat broken
implementations is desired.
The following modifying options are available:
SSL_OP_TLS_ROLLBACK_BUG
Disable version rollback attack detection.
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.)
SSL_OP_SINGLE_DH_USE
Always create a new key when using temporary/ephemeral
DH parameters (see 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
"strong" primes (e.g. when using DSA-parameters, see
dhparam(1)). If "strong" primes were used, it is not
strictly necessary to generate a new DH key during each
handshake but it is also recommended.
SSL_OP_SINGLE_DH_USE should therefore be enabled
whenever temporary/ephemeral DH parameters are used.
SSL_OP_EPHEMERAL_RSA
This option is no longer implemented and is treated as
no op.
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 clients preferences. When
set, the SSLv3/TLSv1 server will choose following its
1.0.2t Last change: 2019-09-10 3
SSL_CTX_set_options(3) OpenSSL SSL_CTX_set_options(3)
own preferences. Because of the different protocol, for
SSLv2 the server will send its list of preferences to
the client and the client chooses.
SSL_OP_PKCS1_CHECK_1
...
SSL_OP_PKCS1_CHECK_2
...
SSL_OP_NETSCAPE_CA_DN_BUG
If we accept a netscape connection, demand a client
cert, have a non-self-signed CA which does not have its
CA in netscape, and the browser has a cert, it will
crash/hang. Works for 3.x and 4.xbeta
SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
...
SSL_OP_NO_SSLv2
Do not use the SSLv2 protocol. As of OpenSSL 1.0.2g the
SSL_OP_NO_SSLv2 option is set by default.
SSL_OP_NO_SSLv3
Do not use the SSLv3 protocol. It is recommended that
applications should set this option.
SSL_OP_NO_TLSv1
Do not use the TLSv1 protocol.
SSL_OP_NO_TLSv1_1
Do not use the TLSv1.1 protocol.
SSL_OP_NO_TLSv1_2
Do not use the TLSv1.2 protocol.
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.
SSL_OP_NO_TICKET
Normally clients and servers will, where possible,
transparently make use of RFC4507bis tickets for
stateless session resumption.
If this option is set this functionality is disabled and
tickets will not be used by clients or servers.
SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
Allow legacy insecure renegotiation between OpenSSL and
1.0.2t Last change: 2019-09-10 4
SSL_CTX_set_options(3) OpenSSL SSL_CTX_set_options(3)
unpatched clients or servers. See the SECURE
RENEGOTIATION section for more details.
SSL_OP_LEGACY_SERVER_CONNECT
Allow legacy insecure renegotiation between OpenSSL and
unpatched servers only: this option is currently set by
default. See the SECURE RENEGOTIATION section for more
details.
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.
The deprecated and highly broken SSLv2 protocol does not
support renegotiation at all: its use is strongly
discouraged.
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 patched. A server not supporting secure renegotiation
is referred to as unpatched.
The following sections describe the operations permitted by
OpenSSL's secure renegotiation implementation.
Patched client and server
Connections and renegotiation are always permitted by
OpenSSL implementations.
Unpatched client and patched OpenSSL server
The initial connection succeeds but client renegotiation is
denied by the server with a no_renegotiation warning alert
if TLS v1.0 is used or a fatal handshake_failure alert in
SSL v3.0.
If the patched OpenSSL server attempts to renegotiate a
fatal handshake_failure alert is sent. This is because the
server code may be unaware of the unpatched nature of the
client.
If the option SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION is
set then renegotiation always succeeds.
NB: 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 no_renegotiation alert. OpenSSL versions
0.9.8m and later will regard a no_renegotiation alert as
fatal and respond with a fatal handshake_failure alert. This
1.0.2t Last change: 2019-09-10 5
SSL_CTX_set_options(3) OpenSSL SSL_CTX_set_options(3)
is because the OpenSSL API currently has no provision to
indicate to an application that a renegotiation attempt was
refused.
Patched OpenSSL client and unpatched server.
If the option SSL_OP_LEGACY_SERVER_CONNECT or
SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION 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.
The option 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.
As more servers become patched the option
SSL_OP_LEGACY_SERVER_CONNECT will not be set by default in a
future version of OpenSSL.
OpenSSL client applications wishing to ensure they can
connect to unpatched servers should always set
SSL_OP_LEGACY_SERVER_CONNECT
OpenSSL client applications that want to ensure they can not
connect to unpatched servers (and thus avoid any security
issues) should always clear SSL_OP_LEGACY_SERVER_CONNECT
using SSL_CTX_clear_options() or SSL_clear_options().
The difference between the SSL_OP_LEGACY_SERVER_CONNECT and
SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION options is that
SSL_OP_LEGACY_SERVER_CONNECT enables initial connections and
secure renegotiation between OpenSSL clients and unpatched
servers only, while SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
allows initial connections and renegotiation between OpenSSL
and unpatched clients or servers.
RETURN VALUES
SSL_CTX_set_options() and SSL_set_options() return the new
options bitmask after adding options.
SSL_CTX_clear_options() and SSL_clear_options() return the
new options bitmask after clearing options.
SSL_CTX_get_options() and SSL_get_options() return the
current bitmask.
1.0.2t Last change: 2019-09-10 6
SSL_CTX_set_options(3) OpenSSL SSL_CTX_set_options(3)
SSL_get_secure_renegotiation_support() returns 1 is the peer
supports secure renegotiation and 0 if it does not.
SEE ALSO
ssl(3), SSL_new(3), SSL_clear(3),
SSL_CTX_set_tmp_dh_callback(3),
SSL_CTX_set_tmp_rsa_callback(3), dhparam(1)
HISTORY
SSL_OP_CIPHER_SERVER_PREFERENCE and
SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION have been
added in OpenSSL 0.9.7.
SSL_OP_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6 and
was automatically enabled with SSL_OP_ALL. As of 0.9.7, it
is no longer included in SSL_OP_ALL and must be explicitly
set.
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).
SSL_CTX_clear_options() and SSL_clear_options() were first
added in OpenSSL 0.9.8m.
SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION,
SSL_OP_LEGACY_SERVER_CONNECT and the function
SSL_get_secure_renegotiation_support() were first added in
OpenSSL 0.9.8m.
1.0.2t Last change: 2019-09-10 7
See also SSL_CTX_clear_options(3)
See also SSL_CTX_get_options(3)
See also SSL_CTX_set_options(3)
See also SSL_clear_options(3)
See also SSL_get_options(3)
See also SSL_get_secure_renegotiation_support(3)
Man(1) output converted with
man2html