|SSL_CTX_SET_OPTIONS(3)||Library Functions Manual||SSL_CTX_SET_OPTIONS(3)|
manipulate SSL options
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
SSL_clear_options() clears the options set
via bitmask in options to
SSL_CTX_get_options() returns the options
set for ctx.
SSL_get_options() returns the options set
indicates whether the peer supports secure renegotiation.
All these functions are implemented using macros.
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 (|).
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
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(3), 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:
It is usually safe to use
enable the bug workaround options if compatibility with somewhat broken
implementations is desired.
The following modifying options are available:
If this option is set this functionality is disabled and tickets will not be used by clients or servers.
The following options used to be supported at some point in the
past and no longer have any effect:
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.
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.
Connections and renegotiation are always permitted by OpenSSL implementations.
The initial connection succeeds but client renegotiation is denied by the server with a no_renegotiation warning alert.
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.
Note that 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 is because the OpenSSL API currently has no provision to indicate to an application that a renegotiation attempt was refused.
If the option
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.
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
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
OpenSSL client applications that want to ensure they can
not connect to unpatched servers (and thus avoid any
security issues) should always clear
SSL_set_options() return the new options bitmask
after adding options.
SSL_clear_options() return the new options bitmask
after clearing options.
SSL_get_options() return the current bitmask.
returns 1 is the peer supports secure renegotiation and 0 if it does
SSL_set_options() first appeared in SSLeay 0.9.0 and
have been available since OpenBSD 2.4.
SSL_get_options() first appeared in OpenSSL 0.9.2b
and have been available since OpenBSD 2.6.
appeared in OpenSSL 0.9.8m and have been available since
|April 11, 2018||OpenBSD-current|