267 lines
10 KiB
Groff
Executable File
267 lines
10 KiB
Groff
Executable File
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.\" ========================================================================
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.\"
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.IX Title "SSL_CTX_SET_CT_VALIDATION_CALLBACK 3"
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.TH SSL_CTX_SET_CT_VALIDATION_CALLBACK 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_ct_validation_cb,
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SSL_enable_ct, SSL_CTX_enable_ct, SSL_disable_ct, SSL_CTX_disable_ct,
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SSL_set_ct_validation_callback, SSL_CTX_set_ct_validation_callback,
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SSL_ct_is_enabled, SSL_CTX_ct_is_enabled \-
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control Certificate Transparency policy
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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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\& typedef int (*ssl_ct_validation_cb)(const CT_POLICY_EVAL_CTX *ctx,
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\& const STACK_OF(SCT) *scts, void *arg);
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\&
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\& int SSL_enable_ct(SSL *s, int validation_mode);
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\& int SSL_CTX_enable_ct(SSL_CTX *ctx, int validation_mode);
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\& int SSL_set_ct_validation_callback(SSL *s, ssl_ct_validation_cb callback,
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\& void *arg);
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\& int SSL_CTX_set_ct_validation_callback(SSL_CTX *ctx,
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\& ssl_ct_validation_cb callback,
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\& void *arg);
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\& void SSL_disable_ct(SSL *s);
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\& void SSL_CTX_disable_ct(SSL_CTX *ctx);
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\& int SSL_ct_is_enabled(const SSL *s);
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\& int SSL_CTX_ct_is_enabled(const SSL_CTX *ctx);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fISSL_enable_ct()\fR and \fISSL_CTX_enable_ct()\fR enable the processing of signed
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certificate timestamps (SCTs) either for a given \s-1SSL\s0 connection or for all
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connections that share the given \s-1SSL\s0 context, respectively.
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This is accomplished by setting a built-in \s-1CT\s0 validation callback.
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The behaviour of the callback is determined by the \fBvalidation_mode\fR argument,
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which can be either of \fB\s-1SSL_CT_VALIDATION_PERMISSIVE\s0\fR or
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\&\fB\s-1SSL_CT_VALIDATION_STRICT\s0\fR as described below.
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.PP
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If \fBvalidation_mode\fR is equal to \fB\s-1SSL_CT_VALIDATION_STRICT\s0\fR, then in a full
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\&\s-1TLS\s0 handshake with the verification mode set to \fB\s-1SSL_VERIFY_PEER\s0\fR, if the peer
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presents no valid SCTs the handshake will be aborted.
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If the verification mode is \fB\s-1SSL_VERIFY_NONE\s0\fR, the handshake will continue
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despite lack of valid SCTs.
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However, in that case if the verification status before the built-in callback
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was \fBX509_V_OK\fR it will be set to \fBX509_V_ERR_NO_VALID_SCTS\fR after the
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callback.
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Applications can call \fISSL_get_verify_result\fR\|(3) to check the status at
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handshake completion, even after session resumption since the verification
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status is part of the saved session state.
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See \fISSL_set_verify\fR\|(3), <\fISSL_get_verify_result\fR\|(3)>, \fISSL_session_reused\fR\|(3).
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.PP
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If \fBvalidation_mode\fR is equal to \fB\s-1SSL_CT_VALIDATION_PERMISSIVE\s0\fR, then the
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handshake continues, and the verification status is not modified, regardless of
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the validation status of any SCTs.
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The application can still inspect the validation status of the SCTs at
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handshake completion.
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Note that with session resumption there will not be any SCTs presented during
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the handshake.
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Therefore, in applications that delay \s-1SCT\s0 policy enforcement until after
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handshake completion, such delayed \s-1SCT\s0 checks should only be performed when the
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session is not resumed.
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.PP
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\&\fISSL_set_ct_validation_callback()\fR and \fISSL_CTX_set_ct_validation_callback()\fR
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register a custom callback that may implement a different policy than either of
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the above.
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This callback can examine the peer's SCTs and determine whether they are
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sufficient to allow the connection to continue.
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The \s-1TLS\s0 handshake is aborted if the verification mode is not \fB\s-1SSL_VERIFY_NONE\s0\fR
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and the callback returns a non-positive result.
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.PP
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An arbitrary callback data argument, \fBarg\fR, can be passed in when setting
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the callback.
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This will be passed to the callback whenever it is invoked.
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Ownership of this context remains with the caller.
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.PP
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If no callback is set, SCTs will not be requested and Certificate Transparency
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validation will not occur.
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.PP
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No callback will be invoked when the peer presents no certificate, e.g. by
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employing an anonymous (aNULL) cipher suite.
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In that case the handshake continues as it would had no callback been
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requested.
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Callbacks are also not invoked when the peer certificate chain is invalid or
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validated via \s-1\fIDANE\-TA\s0\fR\|(2) or \s-1\fIDANE\-EE\s0\fR\|(3) \s-1TLSA\s0 records which use a private X.509
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\&\s-1PKI\s0, or no X.509 \s-1PKI\s0 at all, respectively.
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Clients that require SCTs are expected to not have enabled any aNULL ciphers
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nor to have specified server verification via \s-1\fIDANE\-TA\s0\fR\|(2) or \s-1\fIDANE\-EE\s0\fR\|(3) \s-1TLSA\s0
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records.
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.PP
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\&\fISSL_disable_ct()\fR and \fISSL_CTX_disable_ct()\fR turn off \s-1CT\s0 processing, whether
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enabled via the built-in or the custom callbacks, by setting a \s-1NULL\s0 callback.
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These may be implemented as macros.
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.PP
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\&\fISSL_ct_is_enabled()\fR and \fISSL_CTX_ct_is_enabled()\fR return 1 if \s-1CT\s0 processing is
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enabled via either \fISSL_enable_ct()\fR or a non-null custom callback, and 0
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otherwise.
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.SH "NOTES"
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.IX Header "NOTES"
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When \s-1SCT\s0 processing is enabled, \s-1OCSP\s0 stapling will be enabled. This is because
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one possible source of SCTs is the \s-1OCSP\s0 response from a server.
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.PP
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The time returned by \fISSL_SESSION_get_time()\fR will be used to evaluate whether any
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presented SCTs have timestamps that are in the future (and therefore invalid).
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.SH "RESTRICTIONS"
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.IX Header "RESTRICTIONS"
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Certificate Transparency validation cannot be enabled and so a callback cannot
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be set if a custom client extension handler has been registered to handle \s-1SCT\s0
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extensions (\fBTLSEXT_TYPE_signed_certificate_timestamp\fR).
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fISSL_enable_ct()\fR, \fISSL_CTX_enable_ct()\fR, \fISSL_CTX_set_ct_validation_callback()\fR and
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\&\fISSL_set_ct_validation_callback()\fR return 1 if the \fBcallback\fR is successfully
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set.
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They return 0 if an error occurs, e.g. a custom client extension handler has
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been setup to handle SCTs.
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.PP
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\&\fISSL_disable_ct()\fR and \fISSL_CTX_disable_ct()\fR do not return a result.
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.PP
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\&\fISSL_CTX_ct_is_enabled()\fR and \fISSL_ct_is_enabled()\fR return a 1 if a non-null \s-1CT\s0
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validation callback is set, or 0 if no callback (or equivalently a \s-1NULL\s0
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callback) is set.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIssl\fR\|(7),
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<\fISSL_get_verify_result\fR\|(3)>,
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\&\fISSL_session_reused\fR\|(3),
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\&\fISSL_set_verify\fR\|(3),
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\&\fISSL_CTX_set_verify\fR\|(3),
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\&\fISSL_SESSION_get_time\fR\|(3)
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2016\-2017 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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