326 lines
12 KiB
Groff
326 lines
12 KiB
Groff
.\" $NetBSD: SSL_CTX_set_options.3,v 1.4 2002/07/31 01:45:27 itojun Exp $
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.\" ======================================================================
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.\"
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.IX Title "SSL_CTX_set_options 3"
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.TH SSL_CTX_set_options 3 "0.9.6e" "2002-07-31" "OpenSSL"
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.UC
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.SH "NAME"
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SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options, SSL_get_options \- manipulate \s-1SSL\s0 engine options
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.SH "LIBRARY"
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libcrypto, -lcrypto
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/ssl.h>
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.Ve
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.Vb 2
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\& long SSL_CTX_set_options(SSL_CTX *ctx, long options);
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\& long SSL_set_options(SSL *ssl, long options);
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.Ve
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.Vb 2
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\& long SSL_CTX_get_options(SSL_CTX *ctx);
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\& long SSL_get_options(SSL *ssl);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fISSL_CTX_set_options()\fR adds the options set via bitmask in \fBoptions\fR to \fBctx\fR.
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Options already set before are not cleared!
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.PP
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\&\fISSL_set_options()\fR adds the options set via bitmask in \fBoptions\fR to \fBssl\fR.
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Options already set before are not cleared!
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.PP
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\&\fISSL_CTX_get_options()\fR returns the options set for \fBctx\fR.
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.PP
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\&\fISSL_get_options()\fR returns the options set for \fBssl\fR.
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.SH "NOTES"
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.IX Header "NOTES"
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The behaviour of the \s-1SSL\s0 library can be changed by setting several options.
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The options are coded as bitmasks and can be combined by a logical \fBor\fR
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operation (|). Options can only be added but can never be reset.
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.PP
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\&\fISSL_CTX_set_options()\fR and \fISSL_set_options()\fR affect the (external)
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protocol behaviour of the \s-1SSL\s0 library. The (internal) behaviour of
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the \s-1API\s0 can be changed by using the similar
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SSL_CTX_set_mode(3) and \fISSL_set_mode()\fR functions.
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.PP
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During a handshake, the option settings of the \s-1SSL\s0 object are used. When
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a new \s-1SSL\s0 object is created from a context using \fISSL_new()\fR, the current
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option setting is copied. Changes to \fBctx\fR do not affect already created
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\&\s-1SSL\s0 objects. \fISSL_clear()\fR does not affect the settings.
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.PP
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The following \fBbug workaround\fR options are available:
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.Ip "\s-1SSL_OP_MICROSOFT_SESS_ID_BUG\s0" 4
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.IX Item "SSL_OP_MICROSOFT_SESS_ID_BUG"
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www.microsoft.com \- when talking SSLv2, if session-id reuse is
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performed, the session-id passed back in the server-finished message
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is different from the one decided upon.
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.Ip "\s-1SSL_OP_NETSCAPE_CHALLENGE_BUG\s0" 4
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.IX Item "SSL_OP_NETSCAPE_CHALLENGE_BUG"
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Netscape-Commerce/1.12, when talking SSLv2, accepts a 32 byte
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challenge but then appears to only use 16 bytes when generating the
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encryption keys. Using 16 bytes is ok but it should be ok to use 32.
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According to the SSLv3 spec, one should use 32 bytes for the challenge
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when operating in SSLv2/v3 compatibility mode, but as mentioned above,
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this breaks this server so 16 bytes is the way to go.
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.Ip "\s-1SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG\s0" 4
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.IX Item "SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG"
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ssl3.netscape.com:443, first a connection is established with \s-1RC4\-MD5\s0.
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If it is then resumed, we end up using \s-1DES-CBC3\-SHA\s0. It should be
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\&\s-1RC4\-MD5\s0 according to 7.6.1.3, 'cipher_suite'.
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.Sp
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Netscape-Enterprise/2.01 (https://merchant.netscape.com) has this bug.
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It only really shows up when connecting via SSLv2/v3 then reconnecting
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via SSLv3. The cipher list changes....
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.Sp
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\&\s-1NEW\s0 \s-1INFORMATION\s0. Try connecting with a cipher list of just
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\&\s-1DES-CBC-SHA:RC4\-MD5\s0. For some weird reason, each new connection uses
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\&\s-1RC4\-MD5\s0, but a re-connect tries to use \s-1DES-CBC-SHA\s0. So netscape, when
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doing a re-connect, always takes the first cipher in the cipher list.
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.Ip "\s-1SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG\s0" 4
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.IX Item "SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG"
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\&...
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.Ip "\s-1SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER\s0" 4
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.IX Item "SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER"
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\&...
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.Ip "\s-1SSL_OP_MSIE_SSLV2_RSA_PADDING\s0" 4
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.IX Item "SSL_OP_MSIE_SSLV2_RSA_PADDING"
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\&...
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.Ip "\s-1SSL_OP_SSLEAY_080_CLIENT_DH_BUG\s0" 4
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.IX Item "SSL_OP_SSLEAY_080_CLIENT_DH_BUG"
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\&...
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.Ip "\s-1SSL_OP_TLS_D5_BUG\s0" 4
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.IX Item "SSL_OP_TLS_D5_BUG"
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\&...
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.Ip "\s-1SSL_OP_TLS_BLOCK_PADDING_BUG\s0" 4
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.IX Item "SSL_OP_TLS_BLOCK_PADDING_BUG"
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\&...
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.Ip "\s-1SSL_OP_TLS_ROLLBACK_BUG\s0" 4
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.IX Item "SSL_OP_TLS_ROLLBACK_BUG"
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Disable version rollback attack detection.
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.Sp
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During the client key exchange, the client must send the same information
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about acceptable \s-1SSL/TLS\s0 protocol levels as during the first hello. Some
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clients violate this rule by adapting to the server's answer. (Example:
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the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
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only understands up to SSLv3. In this case the client must still use the
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same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
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to the server's answer and violate the version rollback protection.)
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.Ip "\s-1SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS\s0" 4
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.IX Item "SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS"
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Disables a countermeasure against a \s-1SSL\s0 3.0/TLS 1.0 protocol
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vulnerability affecting \s-1CBC\s0 ciphers, which cannot be handled by some
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broken \s-1SSL\s0 implementations. This option has no effect for connections
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using other ciphers.
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.Ip "\s-1SSL_OP_ALL\s0" 4
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.IX Item "SSL_OP_ALL"
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All of the above bug workarounds.
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.PP
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It is usually safe to use \fB\s-1SSL_OP_ALL\s0\fR to enable the bug workaround
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options if compatibility with somewhat broken implementations is
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desired.
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.PP
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The following \fBmodifying\fR options are available:
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.Ip "\s-1SSL_OP_SINGLE_DH_USE\s0" 4
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.IX Item "SSL_OP_SINGLE_DH_USE"
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Always create a new key when using temporary/ephemeral \s-1DH\s0 parameters
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(see SSL_CTX_set_tmp_dh_callback(3)).
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This option must be used to prevent small subgroup attacks, when
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the \s-1DH\s0 parameters were not generated using \*(L"strong\*(R" primes
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(e.g. when using DSA-parameters, see openssl_dhparam(1)).
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If \*(L"strong\*(R" primes were used, it is not strictly necessary to generate
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a new \s-1DH\s0 key during each handshake but it is also recommended.
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\&\s-1SSL_OP_SINGLE_DH_USE\s0 should therefore be enabled whenever
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temporary/ephemeral \s-1DH\s0 parameters are used.
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.Ip "\s-1SSL_OP_EPHEMERAL_RSA\s0" 4
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.IX Item "SSL_OP_EPHEMERAL_RSA"
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Always use ephemeral (temporary) \s-1RSA\s0 key when doing \s-1RSA\s0 operations
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(see SSL_CTX_set_tmp_rsa_callback(3)).
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According to the specifications this is only done, when a \s-1RSA\s0 key
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can only be used for signature operations (namely under export ciphers
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with restricted \s-1RSA\s0 keylength). By setting this option, ephemeral
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\&\s-1RSA\s0 keys are always used. This option breaks compatibility with the
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\&\s-1SSL/TLS\s0 specifications and may lead to interoperability problems with
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clients and should therefore never be used. Ciphers with \s-1EDH\s0 (ephemeral
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Diffie-Hellman) key exchange should be used instead.
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.Ip "\s-1SSL_OP_PKCS1_CHECK_1\s0" 4
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.IX Item "SSL_OP_PKCS1_CHECK_1"
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\&...
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.Ip "\s-1SSL_OP_PKCS1_CHECK_2\s0" 4
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.IX Item "SSL_OP_PKCS1_CHECK_2"
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\&...
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.Ip "\s-1SSL_OP_NETSCAPE_CA_DN_BUG\s0" 4
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.IX Item "SSL_OP_NETSCAPE_CA_DN_BUG"
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If we accept a netscape connection, demand a client cert, have a
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non-self-sighed \s-1CA\s0 which does not have it's \s-1CA\s0 in netscape, and the
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browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta
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.Ip "\s-1SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG\s0" 4
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.IX Item "SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG"
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\&...
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.Ip "SSL_OP_NO_SSLv2" 4
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.IX Item "SSL_OP_NO_SSLv2"
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Do not use the SSLv2 protocol.
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.Ip "SSL_OP_NO_SSLv3" 4
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.IX Item "SSL_OP_NO_SSLv3"
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Do not use the SSLv3 protocol.
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.Ip "SSL_OP_NO_TLSv1" 4
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.IX Item "SSL_OP_NO_TLSv1"
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Do not use the TLSv1 protocol.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fISSL_CTX_set_options()\fR and \fISSL_set_options()\fR return the new options bitmask
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after adding \fBoptions\fR.
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.PP
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\&\fISSL_CTX_get_options()\fR and \fISSL_get_options()\fR return the current bitmask.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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ssl(3), SSL_new(3), SSL_clear(3),
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SSL_CTX_set_tmp_dh_callback(3),
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SSL_CTX_set_tmp_rsa_callback(3),
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openssl_dhparam(1)
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\s-1SSL_OP_TLS_ROLLBACK_BUG\s0 has been added in OpenSSL 0.9.6.
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.PP
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\&\fB\s-1SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS\s0\fR has been added in OpenSSL 0.9.6e.
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Versions up to OpenSSL 0.9.6c do not include the countermeasure that
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can be disabled with this option (in OpenSSL 0.9.6d, it was always
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enabled).
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