diff options
Diffstat (limited to 'doc/ssl/SSL_CTX_set_options.pod')
| -rw-r--r-- | doc/ssl/SSL_CTX_set_options.pod | 120 |
1 files changed, 117 insertions, 3 deletions
diff --git a/doc/ssl/SSL_CTX_set_options.pod b/doc/ssl/SSL_CTX_set_options.pod index eaed19080975..06025d13fafb 100644 --- a/doc/ssl/SSL_CTX_set_options.pod +++ b/doc/ssl/SSL_CTX_set_options.pod @@ -2,7 +2,7 @@ =head1 NAME -SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options, SSL_get_options - manipulate SSL engine options +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 =head1 SYNOPSIS @@ -11,26 +11,41 @@ SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options, SSL_get_options - man 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); + =head1 DESCRIPTION +Note: all these functions are implemented using macros. + SSL_CTX_set_options() adds the options set via bitmask in B<options> to B<ctx>. Options already set before are not cleared! SSL_set_options() adds the options set via bitmask in B<options> to B<ssl>. Options already set before are not cleared! +SSL_CTX_clear_options() clears the options set via bitmask in B<options> +to B<ctx>. + +SSL_clear_options() clears the options set via bitmask in B<options> to B<ssl>. + SSL_CTX_get_options() returns the options set for B<ctx>. SSL_get_options() returns the options set for B<ssl>. +SSL_get_secure_renegotiation_support() indicates whether the peer supports +secure renegotiation. + =head1 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 B<or> -operation (|). Options can only be added but can never be reset. +operation (|). SSL_CTX_set_options() and SSL_set_options() affect the (external) protocol behaviour of the SSL library. The (internal) behaviour of @@ -199,7 +214,7 @@ Do not use the TLSv1 protocol. 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. +handshake). This option is not needed for clients. =item SSL_OP_NO_TICKET @@ -210,15 +225,107 @@ is explicitly set when OpenSSL is compiled. If this option is set this functionality is disabled and tickets will not be used by clients or servers. +=item SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION + +Allow legacy insecure renegotiation between OpenSSL and unpatched clients or +servers. See the B<SECURE RENEGOTIATION> section for more details. + +=item SSL_OP_LEGACY_SERVER_CONNECT + +Allow legacy insecure renegotiation between OpenSSL and unpatched servers +B<only>: this option is currently set by default. See the +B<SECURE RENEGOTIATION> section for more details. + =back +=head1 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 B<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 I<patched>. A server not supporting secure +renegotiation is referred to as I<unpatched>. + +The following sections describe the operations permitted by OpenSSL's secure +renegotiation implementation. + +=head2 Patched client and server + +Connections and renegotiation are always permitted by OpenSSL implementations. + +=head2 Unpatched client and patched OpenSSL server + +The initial connection suceeds but client renegotiation is denied by the +server with a B<no_renegotiation> warning alert if TLS v1.0 is used or a fatal +B<handshake_failure> alert in SSL v3.0. + +If the patched OpenSSL server attempts to renegotiate a fatal +B<handshake_failure> alert is sent. This is because the server code may be +unaware of the unpatched nature of the client. + +If the option B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then +renegotiation B<always> succeeds. + +B<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 +B<no_renegotiation> alert. OpenSSL versions 0.9.8m and later will regard +a B<no_renegotiation> alert as fatal and respond with a fatal +B<handshake_failure> alert. This is because the OpenSSL API currently has +no provision to indicate to an application that a renegotiation attempt +was refused. + +=head2 Patched OpenSSL client and unpatched server. + +If the option B<SSL_OP_LEGACY_SERVER_CONNECT> or +B<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 B<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 B<SSL_OP_LEGACY_SERVER_CONNECT> will +B<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 B<set> B<SSL_OP_LEGACY_SERVER_CONNECT> + +OpenSSL client applications that want to ensure they can B<not> connect to +unpatched servers (and thus avoid any security issues) should always B<clear> +B<SSL_OP_LEGACY_SERVER_CONNECT> using SSL_CTX_clear_options() or +SSL_clear_options(). + +The difference between the B<SSL_OP_LEGACY_SERVER_CONNECT> and +B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> options is that +B<SSL_OP_LEGACY_SERVER_CONNECT> enables initial connections and secure +renegotiation between OpenSSL clients and unpatched servers B<only>, while +B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> allows initial connections +and renegotiation between OpenSSL and unpatched clients or servers. + =head1 RETURN VALUES SSL_CTX_set_options() and SSL_set_options() return the new options bitmask after adding B<options>. +SSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask +after clearing B<options>. + SSL_CTX_get_options() and SSL_get_options() return the current bitmask. +SSL_get_secure_renegotiation_support() returns 1 is the peer supports +secure renegotiation and 0 if it does not. + =head1 SEE ALSO L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>, @@ -241,4 +348,11 @@ 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. + +B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>, B<SSL_OP_LEGACY_SERVER_CONNECT> +and the function SSL_get_secure_renegotiation_support() were first added in +OpenSSL 0.9.8m. + =cut |