474 lines
20 KiB
Groff
Executable File
474 lines
20 KiB
Groff
Executable File
.\" Automatically generated by Pod::Man 2.25 (Pod::Simple 3.16)
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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 "2020-03-02" "3.0.0-dev" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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SSL_CTX_set_options, SSL_set_options, SSL_CTX_clear_options,
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SSL_clear_options, SSL_CTX_get_options, SSL_get_options,
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SSL_get_secure_renegotiation_support \- manipulate SSL options
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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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\&
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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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\&
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\& long SSL_CTX_clear_options(SSL_CTX *ctx, long options);
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\& long SSL_clear_options(SSL *ssl, long options);
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\&
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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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\&
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\& long SSL_get_secure_renegotiation_support(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 bit-mask 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 bit-mask 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_clear_options()\fR clears the options set via bit-mask in \fBoptions\fR
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to \fBctx\fR.
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.PP
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\&\fISSL_clear_options()\fR clears the options set via bit-mask in \fBoptions\fR to \fBssl\fR.
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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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.PP
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\&\fISSL_get_secure_renegotiation_support()\fR indicates whether the peer supports
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secure renegotiation.
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Note, this is implemented via a macro.
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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 bit-masks and can be combined by a bitwise \fBor\fR
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operation (|).
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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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\&\fISSL_CTX_set_mode\fR\|(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_SAFARI_ECDHE_ECDSA_BUG\s0" 4
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.IX Item "SSL_OP_SAFARI_ECDHE_ECDSA_BUG"
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Don't prefer ECDHE-ECDSA ciphers when the client appears to be Safari on \s-1OS\s0 X.
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\&\s-1OS\s0 X 10.8..10.8.3 has broken support for ECDHE-ECDSA ciphers.
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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_TLSEXT_PADDING\s0" 4
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.IX Item "SSL_OP_TLSEXT_PADDING"
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Adds a padding extension to ensure the ClientHello size is never between
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256 and 511 bytes in length. This is needed as a workaround for some
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implementations.
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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 plus \fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR as
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mentioned below.
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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_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_CIPHER_SERVER_PREFERENCE\s0" 4
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.IX Item "SSL_OP_CIPHER_SERVER_PREFERENCE"
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When choosing a cipher, use the server's preferences instead of the client
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preferences. When not set, the \s-1SSL\s0 server will always follow the clients
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preferences. When set, the \s-1SSL/TLS\s0 server will choose following its
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own preferences.
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.IP "SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1, SSL_OP_NO_TLSv1_2, SSL_OP_NO_TLSv1_3, SSL_OP_NO_DTLSv1, SSL_OP_NO_DTLSv1_2" 4
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.IX Item "SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1, SSL_OP_NO_TLSv1_2, SSL_OP_NO_TLSv1_3, SSL_OP_NO_DTLSv1, SSL_OP_NO_DTLSv1_2"
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These options turn off the SSLv3, TLSv1, TLSv1.1, TLSv1.2 or TLSv1.3 protocol
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versions with \s-1TLS\s0 or the DTLSv1, DTLSv1.2 versions with \s-1DTLS\s0,
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respectively.
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As of OpenSSL 1.1.0, these options are deprecated, use
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\&\fISSL_CTX_set_min_proto_version\fR\|(3) and
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\&\fISSL_CTX_set_max_proto_version\fR\|(3) instead.
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.IP "\s-1SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION\s0" 4
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.IX Item "SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION"
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When performing renegotiation as a server, always start a new session
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(i.e., session resumption requests are only accepted in the initial
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handshake). This option is not needed for clients.
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.IP "\s-1SSL_OP_NO_COMPRESSION\s0" 4
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.IX Item "SSL_OP_NO_COMPRESSION"
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Do not use compression even if it is supported.
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.IP "\s-1SSL_OP_NO_QUERY_MTU\s0" 4
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.IX Item "SSL_OP_NO_QUERY_MTU"
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Do not query the \s-1MTU\s0. Only affects \s-1DTLS\s0 connections.
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.IP "\s-1SSL_OP_COOKIE_EXCHANGE\s0" 4
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.IX Item "SSL_OP_COOKIE_EXCHANGE"
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Turn on Cookie Exchange as described in \s-1RFC4347\s0 Section 4.2.1. Only affects
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\&\s-1DTLS\s0 connections.
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.IP "\s-1SSL_OP_NO_TICKET\s0" 4
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.IX Item "SSL_OP_NO_TICKET"
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\&\s-1SSL/TLS\s0 supports two mechanisms for resuming sessions: session ids and stateless
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session tickets.
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.Sp
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When using session ids a copy of the session information is
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cached on the server and a unique id is sent to the client. When the client
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wishes to resume it provides the unique id so that the server can retrieve the
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session information from its cache.
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.Sp
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When using stateless session tickets the server uses a session ticket encryption
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key to encrypt the session information. This encrypted data is sent to the
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client as a \*(L"ticket\*(R". When the client wishes to resume it sends the encrypted
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data back to the server. The server uses its key to decrypt the data and resume
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the session. In this way the server can operate statelessly \- no session
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information needs to be cached locally.
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.Sp
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The TLSv1.3 protocol only supports tickets and does not directly support session
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ids. However OpenSSL allows two modes of ticket operation in TLSv1.3: stateful
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and stateless. Stateless tickets work the same way as in TLSv1.2 and below.
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Stateful tickets mimic the session id behaviour available in TLSv1.2 and below.
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The session information is cached on the server and the session id is wrapped up
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in a ticket and sent back to the client. When the client wishes to resume, it
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presents a ticket in the same way as for stateless tickets. The server can then
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extract the session id from the ticket and retrieve the session information from
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its cache.
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.Sp
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By default OpenSSL will use stateless tickets. The \s-1SSL_OP_NO_TICKET\s0 option will
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cause stateless tickets to not be issued. In TLSv1.2 and below this means no
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ticket gets sent to the client at all. In TLSv1.3 a stateful ticket will be
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sent. This is a server-side option only.
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.Sp
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In TLSv1.3 it is possible to suppress all tickets (stateful and stateless) from
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being sent by calling \fISSL_CTX_set_num_tickets\fR\|(3) or
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\&\fISSL_set_num_tickets\fR\|(3).
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.IP "\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0" 4
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.IX Item "SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION"
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Allow legacy insecure renegotiation between OpenSSL and unpatched clients or
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servers. See the \fB\s-1SECURE\s0 \s-1RENEGOTIATION\s0\fR section for more details.
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.IP "\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0" 4
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.IX Item "SSL_OP_LEGACY_SERVER_CONNECT"
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Allow legacy insecure renegotiation between OpenSSL and unpatched servers
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\&\fBonly\fR: this option is currently set by default. See the
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\&\fB\s-1SECURE\s0 \s-1RENEGOTIATION\s0\fR section for more details.
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.IP "\s-1SSL_OP_NO_ENCRYPT_THEN_MAC\s0" 4
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.IX Item "SSL_OP_NO_ENCRYPT_THEN_MAC"
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|
Normally clients and servers will transparently attempt to negotiate the
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\&\s-1RFC7366\s0 Encrypt-then-MAC option on \s-1TLS\s0 and \s-1DTLS\s0 connection.
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.Sp
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If this option is set, Encrypt-then-MAC is disabled. Clients will not
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propose, and servers will not accept the extension.
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.IP "\s-1SSL_OP_NO_EXTENDED_MASTER_SECRET\s0" 4
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.IX Item "SSL_OP_NO_EXTENDED_MASTER_SECRET"
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|
Normally clients and servers will transparently attempt to negotiate the
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\&\s-1RFC7627\s0 Extended Master Secret option on \s-1TLS\s0 and \s-1DTLS\s0 connection.
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.Sp
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If this option is set, Extended Master Secret is disabled. Clients will
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not propose, and servers will not accept the extension.
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.IP "\s-1SSL_OP_NO_RENEGOTIATION\s0" 4
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.IX Item "SSL_OP_NO_RENEGOTIATION"
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Disable all renegotiation in TLSv1.2 and earlier. Do not send HelloRequest
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messages, and ignore renegotiation requests via ClientHello.
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.IP "\s-1SSL_OP_ALLOW_NO_DHE_KEX\s0" 4
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.IX Item "SSL_OP_ALLOW_NO_DHE_KEX"
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In TLSv1.3 allow a non\-(ec)dhe based key exchange mode on resumption. This means
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that there will be no forward secrecy for the resumed session.
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.IP "\s-1SSL_OP_PRIORITIZE_CHACHA\s0" 4
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.IX Item "SSL_OP_PRIORITIZE_CHACHA"
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When \s-1SSL_OP_CIPHER_SERVER_PREFERENCE\s0 is set, temporarily reprioritize
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ChaCha20\-Poly1305 ciphers to the top of the server cipher list if a
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ChaCha20\-Poly1305 cipher is at the top of the client cipher list. This helps
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those clients (e.g. mobile) use ChaCha20\-Poly1305 if that cipher is anywhere
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in the server cipher list; but still allows other clients to use \s-1AES\s0 and other
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ciphers. Requires \fB\s-1SSL_OP_CIPHER_SERVER_PREFERENCE\s0\fR.
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.IP "\s-1SSL_OP_ENABLE_MIDDLEBOX_COMPAT\s0" 4
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.IX Item "SSL_OP_ENABLE_MIDDLEBOX_COMPAT"
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|
If set then dummy Change Cipher Spec (\s-1CCS\s0) messages are sent in TLSv1.3. This
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has the effect of making TLSv1.3 look more like TLSv1.2 so that middleboxes that
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do not understand TLSv1.3 will not drop the connection. Regardless of whether
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this option is set or not \s-1CCS\s0 messages received from the peer will always be
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ignored in TLSv1.3. This option is set by default. To switch it off use
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\&\fISSL_clear_options()\fR. A future version of OpenSSL may not set this by default.
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.IP "\s-1SSL_OP_NO_ANTI_REPLAY\s0" 4
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.IX Item "SSL_OP_NO_ANTI_REPLAY"
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By default, when a server is configured for early data (i.e., max_early_data > 0),
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OpenSSL will switch on replay protection. See \fISSL_read_early_data\fR\|(3) for a
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description of the replay protection feature. Anti-replay measures are required
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to comply with the TLSv1.3 specification. Some applications may be able to
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mitigate the replay risks in other ways and in such cases the built in OpenSSL
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functionality is not required. Those applications can turn this feature off by
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setting this option. This is a server-side opton only. It is ignored by
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clients.
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.PP
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The following options no longer have any effect but their identifiers are
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retained for compatibility purposes:
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.IP "\s-1SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG\s0" 4
|
|
.IX Item "SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG"
|
|
.PD 0
|
|
.IP "\s-1SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER\s0" 4
|
|
.IX Item "SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER"
|
|
.IP "\s-1SSL_OP_SSLEAY_080_CLIENT_DH_BUG\s0" 4
|
|
.IX Item "SSL_OP_SSLEAY_080_CLIENT_DH_BUG"
|
|
.IP "\s-1SSL_OP_TLS_D5_BUG\s0" 4
|
|
.IX Item "SSL_OP_TLS_D5_BUG"
|
|
.IP "\s-1SSL_OP_TLS_BLOCK_PADDING_BUG\s0" 4
|
|
.IX Item "SSL_OP_TLS_BLOCK_PADDING_BUG"
|
|
.IP "\s-1SSL_OP_MSIE_SSLV2_RSA_PADDING\s0" 4
|
|
.IX Item "SSL_OP_MSIE_SSLV2_RSA_PADDING"
|
|
.IP "\s-1SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG\s0" 4
|
|
.IX Item "SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG"
|
|
.IP "\s-1SSL_OP_MICROSOFT_SESS_ID_BUG\s0" 4
|
|
.IX Item "SSL_OP_MICROSOFT_SESS_ID_BUG"
|
|
.IP "\s-1SSL_OP_NETSCAPE_CHALLENGE_BUG\s0" 4
|
|
.IX Item "SSL_OP_NETSCAPE_CHALLENGE_BUG"
|
|
.IP "\s-1SSL_OP_PKCS1_CHECK_1\s0" 4
|
|
.IX Item "SSL_OP_PKCS1_CHECK_1"
|
|
.IP "\s-1SSL_OP_PKCS1_CHECK_2\s0" 4
|
|
.IX Item "SSL_OP_PKCS1_CHECK_2"
|
|
.IP "\s-1SSL_OP_SINGLE_DH_USE\s0" 4
|
|
.IX Item "SSL_OP_SINGLE_DH_USE"
|
|
.IP "\s-1SSL_OP_SINGLE_ECDH_USE\s0" 4
|
|
.IX Item "SSL_OP_SINGLE_ECDH_USE"
|
|
.IP "\s-1SSL_OP_EPHEMERAL_RSA\s0" 4
|
|
.IX Item "SSL_OP_EPHEMERAL_RSA"
|
|
.PD
|
|
.SH "SECURE RENEGOTIATION"
|
|
.IX Header "SECURE RENEGOTIATION"
|
|
OpenSSL always attempts to use secure renegotiation as
|
|
described in \s-1RFC5746\s0. This counters the prefix attack described in
|
|
\&\s-1CVE\-2009\-3555\s0 and elsewhere.
|
|
.PP
|
|
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 \fIpatched\fR. A server not supporting secure
|
|
renegotiation is referred to as \fIunpatched\fR.
|
|
.PP
|
|
The following sections describe the operations permitted by OpenSSL's secure
|
|
renegotiation implementation.
|
|
.SS "Patched client and server"
|
|
.IX Subsection "Patched client and server"
|
|
Connections and renegotiation are always permitted by OpenSSL implementations.
|
|
.SS "Unpatched client and patched OpenSSL server"
|
|
.IX Subsection "Unpatched client and patched OpenSSL server"
|
|
The initial connection succeeds but client renegotiation is denied by the
|
|
server with a \fBno_renegotiation\fR warning alert if \s-1TLS\s0 v1.0 is used or a fatal
|
|
\&\fBhandshake_failure\fR alert in \s-1SSL\s0 v3.0.
|
|
.PP
|
|
If the patched OpenSSL server attempts to renegotiate a fatal
|
|
\&\fBhandshake_failure\fR alert is sent. This is because the server code may be
|
|
unaware of the unpatched nature of the client.
|
|
.PP
|
|
If the option \fB\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0\fR is set then
|
|
renegotiation \fBalways\fR succeeds.
|
|
.SS "Patched OpenSSL client and unpatched server"
|
|
.IX Subsection "Patched OpenSSL client and unpatched server"
|
|
If the option \fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR or
|
|
\&\fB\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0\fR 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.
|
|
.PP
|
|
The option \fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR 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.
|
|
.PP
|
|
As more servers become patched the option \fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR will
|
|
\&\fBnot\fR be set by default in a future version of OpenSSL.
|
|
.PP
|
|
OpenSSL client applications wishing to ensure they can connect to unpatched
|
|
servers should always \fBset\fR \fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR
|
|
.PP
|
|
OpenSSL client applications that want to ensure they can \fBnot\fR connect to
|
|
unpatched servers (and thus avoid any security issues) should always \fBclear\fR
|
|
\&\fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR using \fISSL_CTX_clear_options()\fR or
|
|
\&\fISSL_clear_options()\fR.
|
|
.PP
|
|
The difference between the \fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR and
|
|
\&\fB\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0\fR options is that
|
|
\&\fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR enables initial connections and secure
|
|
renegotiation between OpenSSL clients and unpatched servers \fBonly\fR, while
|
|
\&\fB\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0\fR allows initial connections
|
|
and renegotiation between OpenSSL and unpatched clients or servers.
|
|
.SH "RETURN VALUES"
|
|
.IX Header "RETURN VALUES"
|
|
\&\fISSL_CTX_set_options()\fR and \fISSL_set_options()\fR return the new options bit-mask
|
|
after adding \fBoptions\fR.
|
|
.PP
|
|
\&\fISSL_CTX_clear_options()\fR and \fISSL_clear_options()\fR return the new options bit-mask
|
|
after clearing \fBoptions\fR.
|
|
.PP
|
|
\&\fISSL_CTX_get_options()\fR and \fISSL_get_options()\fR return the current bit-mask.
|
|
.PP
|
|
\&\fISSL_get_secure_renegotiation_support()\fR returns 1 is the peer supports
|
|
secure renegotiation and 0 if it does not.
|
|
.SH "SEE ALSO"
|
|
.IX Header "SEE ALSO"
|
|
\&\fIssl\fR\|(7), \fISSL_new\fR\|(3), \fISSL_clear\fR\|(3),
|
|
\&\fISSL_CTX_set_tmp_dh_callback\fR\|(3),
|
|
\&\fISSL_CTX_set_min_proto_version\fR\|(3),
|
|
\&\fIopenssl\-dhparam\fR\|(1)
|
|
.SH "HISTORY"
|
|
.IX Header "HISTORY"
|
|
The attempt to always try to use secure renegotiation was added in
|
|
OpenSSL 0.9.8m.
|
|
.PP
|
|
The \fB\s-1SSL_OP_PRIORITIZE_CHACHA\s0\fR and \fB\s-1SSL_OP_NO_RENEGOTIATION\s0\fR options
|
|
were added in OpenSSL 1.1.1.
|
|
.PP
|
|
The \fB\s-1SSL_OP_NO_EXTENDED_MASTER_SECRET\s0\fR option was added in OpenSSL 3.0.
|
|
.SH "COPYRIGHT"
|
|
.IX Header "COPYRIGHT"
|
|
Copyright 2001\-2019 The OpenSSL Project Authors. All Rights Reserved.
|
|
.PP
|
|
Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
|
|
this file except in compliance with the License. You can obtain a copy
|
|
in the file \s-1LICENSE\s0 in the source distribution or at
|
|
<https://www.openssl.org/source/license.html>.
|