OpenSSL SSL_CTX_set_options(3openssl)
NNNNAAAAMMMMEEEESSL_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 SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS#include
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);
DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN Note: all these functions are implemented using macros.SSL_CTX_set_options() adds the options set via bitmask in
ooooppppttttiiiioooonnnnssss to ccccttttxxxx. Options already set before are not cleared!SSL_set_options() adds the options set via bitmask in
ooooppppttttiiiioooonnnnssss to ssssssssllll. Options already set before are not cleared!SSL_CTX_clear_options() clears the options set via bitmask
in ooooppppttttiiiioooonnnnssss to ccccttttxxxx.SSL_clear_options() clears the options set via bitmask in
ooooppppttttiiiioooonnnnssss to ssssssssllll.SSL_CTX_get_options() returns the options set for ccccttttxxxx.
SSL_get_options() returns the options set for ssssssssllll.
SSL_get_secure_renegotiation_support() indicates whether the
peer supports secure renegotiation. NNNNOOOOTTTTEEEESSSS 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 oooorrrr 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 thesimilar SSL_CTX_set_mode(3) and SSL_set_mode() functions.
18/Feb/2010 Last change: 0.9.8o 1
OpenSSL SSL_CTX_set_options(3openssl)
During a handshake, the option settings of the SSL object are used. When a new SSL object is created from a contextusing SSL_new(), the current option setting is copied.
Changes to ccccttttxxxx do not affect already created SSL objects.SSL_clear() does not affect the settings.
The following bbbbuuuugggg wwwwoooorrrrkkkkaaaarrrroooouuuunnnndddd 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
ssl3.netscape.com:443, first a connection is establishedwith RC4-MD5. If it is then resumed, we end up using
DES-CBC3-SHA. It should be RC4-MD5 according to
7.6.1.3, 'cipher_suite'.
Netscape-Enterprise/2.01 (https://merchant.netscape.com)
has this bug. It only really shows up when connecting via SSLv2/v3 then reconnecting via SSLv3. The cipher list changes.... NEW INFORMATION. Try connecting with a cipher list ofjust DES-CBC-SHA:RC4-MD5. For some weird reason, each
new connection uses RC4-MD5, but a re-connect tries to
use DES-CBC-SHA. So netscape, when doing a re-connect,
always takes the first cipher in the cipher list.SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
...SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
...SSL_OP_MSIE_SSLV2_RSA_PADDING
As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect.18/Feb/2010 Last change: 0.9.8o 2
OpenSSL SSL_CTX_set_options(3openssl)
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. This option has no effect for connections using other ciphers.
SSL_OP_ALL
All of the above bug workarounds.It is usually safe to use SSSSSSSSLLLL_OOOOPPPP_AAAALLLLLLLL to enable the bug
workaround options if compatibility with somewhat broken implementations is desired. The following mmmmooooddddiiiiffffyyyyiiiinnnngggg options are available:SSL_OP_TLS_ROLLBACK_BUG
Disable version rollback attack detection. During the client key exchange, the client must send thesame 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/ephemeralDH 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.SSSSSSSSLLLL_OOOOPPPP_SSSSIIIINNNNGGGGLLLLEEEE_DDDDHHHH_UUUUSSSSEEEE should therefore be enabled
whenever temporary/ephemeral DH parameters are used.18/Feb/2010 Last change: 0.9.8o 3
OpenSSL SSL_CTX_set_options(3openssl)
SSL_OP_EPHEMERAL_RSA
Always use ephemeral (temporary) RSA key when doing RSAoperations (see 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 withthe 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.
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. Whenset, 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.
SSL_OP_PKCS1_CHECK_1
...SSL_OP_PKCS1_CHECK_2
...SSL_OP_NETSCAPE_CA_DN_BUG
If we accept a netscape connection, demand a clientcert, 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.xbetaSSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
...SSL_OP_NO_SSLv2
Do not use the SSLv2 protocol.SSL_OP_NO_SSLv3
Do not use the SSLv3 protocol.SSL_OP_NO_TLSv1
Do not use the TLSv1 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.18/Feb/2010 Last change: 0.9.8o 4
OpenSSL SSL_CTX_set_options(3openssl)
SSL_OP_NO_TICKET
Normally clients and servers will, where possible, transparently make use of RFC4507bis tickets for stateless session resumption if extension support 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.SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
Allow legacy insecure renegotiation between OpenSSL and unpatched clients or servers. See the SSSSEEEECCCCUUUURRRREEEE RRRREEEENNNNEEEEGGGGOOOOTTTTIIIIAAAATTTTIIIIOOOONNNN section for more details.SSL_OP_LEGACY_SERVER_CONNECT
Allow legacy insecure renegotiation between OpenSSL and unpatched servers oooonnnnllllyyyy: this option is currently set by default. See the SSSSEEEECCCCUUUURRRREEEE RRRREEEENNNNEEEEGGGGOOOOTTTTIIIIAAAATTTTIIIIOOOONNNN section for more details. SSSSEEEECCCCUUUURRRREEEE RRRREEEENNNNEEEEGGGGOOOOTTTTIIIIAAAATTTTIIIIOOOONNNN OpenSSL 0.9.8m and later always attempts to use secure renegotiation as described in RFC5746. This counters theprefix attack described in CVE-2009-3555 and elsewhere.
The deprecated and highly broken SSLv2 protocol does not support renegotiation at all: its use is ssssttttrrrroooonnnnggggllllyyyy 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. PPPPaaaattttcccchhhheeeedddd cccclllliiiieeeennnntttt aaaannnndddd sssseeeerrrrvvvveeeerrrr Connections and renegotiation are always permitted by OpenSSL implementations. UUUUnnnnppppaaaattttcccchhhheeeedddd cccclllliiiieeeennnntttt aaaannnndddd ppppaaaattttcccchhhheeeedddd OOOOppppeeeennnnSSSSSSSSLLLL sssseeeerrrrvvvveeeerrrr The initial connection suceeds but client renegotiation isdenied by the server with a nnnnoooo_rrrreeeennnneeeeggggoooottttiiiiaaaattttiiiioooonnnn warning alert
if TLS v1.0 is used or a fatal hhhhaaaannnnddddsssshhhhaaaakkkkeeee_ffffaaaaiiiilllluuuurrrreeee alert in
SSL v3.0. If the patched OpenSSL server attempts to renegotiate afatal hhhhaaaannnnddddsssshhhhaaaakkkkeeee_ffffaaaaiiiilllluuuurrrreeee alert is sent. This is because the
18/Feb/2010 Last change: 0.9.8o 5
OpenSSL SSL_CTX_set_options(3openssl)
server code may be unaware of the unpatched nature of the client.If the option SSSSSSSSLLLL_OOOOPPPP_AAAALLLLLLLLOOOOWWWW_UUUUNNNNSSSSAAAAFFFFEEEE_LLLLEEEEGGGGAAAACCCCYYYY_RRRREEEENNNNEEEEGGGGOOOOTTTTIIIIAAAATTTTIIIIOOOONNNN is
set then renegotiation aaaallllwwwwaaaayyyyssss succeeds. NNNNBBBB:::: a bug in OpenSSL clients earlier than 0.9.8m (all of which are unpatched) will result in the connection hangingif it receives a nnnnoooo_rrrreeeennnneeeeggggoooottttiiiiaaaattttiiiioooonnnn alert. OpenSSL versions
0.9.8m and later will regard a nnnnoooo_rrrreeeennnneeeeggggoooottttiiiiaaaattttiiiioooonnnn alert as
fatal and respond with a fatal hhhhaaaannnnddddsssshhhhaaaakkkkeeee_ffffaaaaiiiilllluuuurrrreeee alert. This
is because the OpenSSL API currently has no provision to indicate to an application that a renegotiation attempt was refused. PPPPaaaattttcccchhhheeeedddd OOOOppppeeeennnnSSSSSSSSLLLL cccclllliiiieeeennnntttt aaaannnndddd uuuunnnnppppaaaattttcccchhhheeeedddd sssseeeerrrrvvvveeeerrrr....If the option SSSSSSSSLLLL_OOOOPPPP_LLLLEEEEGGGGAAAACCCCYYYY_SSSSEEEERRRRVVVVEEEERRRR_CCCCOOOONNNNNNNNEEEECCCCTTTT or
SSSSSSSSLLLL_OOOOPPPP_AAAALLLLLLLLOOOOWWWW_UUUUNNNNSSSSAAAAFFFFEEEE_LLLLEEEEGGGGAAAACCCCYYYY_RRRREEEENNNNEEEEGGGGOOOOTTTTIIIIAAAATTTTIIIIOOOONNNN 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 SSSSSSSSLLLL_OOOOPPPP_LLLLEEEEGGGGAAAACCCCYYYY_SSSSEEEERRRRVVVVEEEERRRR_CCCCOOOONNNNNNNNEEEECCCCTTTT 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 optionSSSSSSSSLLLL_OOOOPPPP_LLLLEEEEGGGGAAAACCCCYYYY_SSSSEEEERRRRVVVVEEEERRRR_CCCCOOOONNNNNNNNEEEECCCCTTTT will nnnnooootttt be set by default in a
future version of OpenSSL. OpenSSL client applications wishing to ensure they can connect to unpatched servers should always sssseeeettttSSSSSSSSLLLL_OOOOPPPP_LLLLEEEEGGGGAAAACCCCYYYY_SSSSEEEERRRRVVVVEEEERRRR_CCCCOOOONNNNNNNNEEEECCCCTTTT
OpenSSL client applications that want to ensure they can nnnnooootttt connect to unpatched servers (and thus avoid any securityissues) should always cccclllleeeeaaaarrrr SSSSSSSSLLLL_OOOOPPPP_LLLLEEEEGGGGAAAACCCCYYYY_SSSSEEEERRRRVVVVEEEERRRR_CCCCOOOONNNNNNNNEEEECCCCTTTT
using SSL_CTX_clear_options() or SSL_clear_options().
The difference between the SSSSSSSSLLLL_OOOOPPPP_LLLLEEEEGGGGAAAACCCCYYYY_SSSSEEEERRRRVVVVEEEERRRR_CCCCOOOONNNNNNNNEEEECCCCTTTT and
SSSSSSSSLLLL_OOOOPPPP_AAAALLLLLLLLOOOOWWWW_UUUUNNNNSSSSAAAAFFFFEEEE_LLLLEEEEGGGGAAAACCCCYYYY_RRRREEEENNNNEEEEGGGGOOOOTTTTIIIIAAAATTTTIIIIOOOONNNN options is that
SSSSSSSSLLLL_OOOOPPPP_LLLLEEEEGGGGAAAACCCCYYYY_SSSSEEEERRRRVVVVEEEERRRR_CCCCOOOONNNNNNNNEEEECCCCTTTT enables initial connections and
secure renegotiation between OpenSSL clients and unpatchedservers oooonnnnllllyyyy, while SSSSSSSSLLLL_OOOOPPPP_AAAALLLLLLLLOOOOWWWW_UUUUNNNNSSSSAAAAFFFFEEEE_LLLLEEEEGGGGAAAACCCCYYYY_RRRREEEENNNNEEEEGGGGOOOOTTTTIIIIAAAATTTTIIIIOOOONNNN
allows initial connections and renegotiation between OpenSSL and unpatched clients or servers.18/Feb/2010 Last change: 0.9.8o 6
OpenSSL SSL_CTX_set_options(3openssl)
RRRREEEETTTTUUUURRRRNNNN VVVVAAAALLLLUUUUEEEESSSSSSL_CTX_set_options() and SSL_set_options() return the new
options bitmask after adding ooooppppttttiiiioooonnnnssss.SSL_CTX_clear_options() and SSL_clear_options() return the
new options bitmask after clearing ooooppppttttiiiioooonnnnssss.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. SSSSEEEEEEEE AAAALLLLSSSSOOOOssl(3), SSL_new(3), SSL_clear(3),
SSL_CTX_set_tmp_dh_callback(3),
SSL_CTX_set_tmp_rsa_callback(3), dhparam(1)
HHHHIIIISSSSTTTTOOOORRRRYYYYSSSSSSSSLLLL_OOOOPPPP_CCCCIIIIPPPPHHHHEEEERRRR_SSSSEEEERRRRVVVVEEEERRRR_PPPPRRRREEEEFFFFEEEERRRREEEENNNNCCCCEEEE and
SSSSSSSSLLLL_OOOOPPPP_NNNNOOOO_SSSSEEEESSSSSSSSIIIIOOOONNNN_RRRREEEESSSSUUUUMMMMPPPPTTTTIIIIOOOONNNN_OOOONNNN_RRRREEEENNNNEEEEGGGGOOOOTTTTIIIIAAAATTTTIIIIOOOONNNN have been
added in OpenSSL 0.9.7.SSSSSSSSLLLL_OOOOPPPP_TTTTLLLLSSSS_RRRROOOOLLLLLLLLBBBBAAAACCCCKKKK_BBBBUUUUGGGG has been added in OpenSSL 0.9.6 and
was automatically enabled with SSSSSSSSLLLL_OOOOPPPP_AAAALLLLLLLL. As of 0.9.7, it
is no longer included in SSSSSSSSLLLL_OOOOPPPP_AAAALLLLLLLL and must be explicitly
set.SSSSSSSSLLLL_OOOOPPPP_DDDDOOOONNNNTTTT_IIIINNNNSSSSEEEERRRRTTTT_EEEEMMMMPPPPTTTTYYYY_FFFFRRRRAAAAGGGGMMMMEEEENNNNTTTTSSSS 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.SSSSSSSSLLLL_OOOOPPPP_AAAALLLLLLLLOOOOWWWW_UUUUNNNNSSSSAAAAFFFFEEEE_LLLLEEEEGGGGAAAACCCCYYYY_RRRREEEENNNNEEEEGGGGOOOOTTTTIIIIAAAATTTTIIIIOOOONNNN,
SSSSSSSSLLLL_OOOOPPPP_LLLLEEEEGGGGAAAACCCCYYYY_SSSSEEEERRRRVVVVEEEERRRR_CCCCOOOONNNNNNNNEEEECCCCTTTT and the function
SSL_get_secure_renegotiation_support() were first added in
OpenSSL 0.9.8m.18/Feb/2010 Last change: 0.9.8o 7
OpenSSL SSL_CTX_set_options(3openssl)
18/Feb/2010 Last change: 0.9.8o 8