225 lines
8.3 KiB
Groff
225 lines
8.3 KiB
Groff
.\" $NetBSD: SSL_CTX_set_client_cert_cb.3,v 1.9 2005/04/24 00:10:03 wiz Exp $
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.\" ========================================================================
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.\"
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.IX Title "SSL_CTX_set_client_cert_cb 3"
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.TH SSL_CTX_set_client_cert_cb 3 "2002-07-31" "0.9.7g" "OpenSSL"
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.SH "NAME"
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SSL_CTX_set_client_cert_cb, SSL_CTX_get_client_cert_cb \- handle client certificate callback function
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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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.PP
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.Vb 3
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\& void SSL_CTX_set_client_cert_cb(SSL_CTX *ctx, int (*client_cert_cb)(SSL *ssl, X509 **x509, EVP_PKEY **pkey));
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\& int (*SSL_CTX_get_client_cert_cb(SSL_CTX *ctx))(SSL *ssl, X509 **x509, EVP_PKEY **pkey);
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\& int (*client_cert_cb)(SSL *ssl, X509 **x509, EVP_PKEY **pkey);
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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_client_cert_cb()\fR sets the \fB\f(BIclient_cert_cb()\fB\fR callback, that is
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called when a client certificate is requested by a server and no certificate
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was yet set for the \s-1SSL\s0 object.
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.PP
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When \fB\f(BIclient_cert_cb()\fB\fR is \s-1NULL\s0, no callback function is used.
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.PP
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\&\fISSL_CTX_get_client_cert_cb()\fR returns a pointer to the currently set callback
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function.
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.PP
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\&\fIclient_cert_cb()\fR is the application defined callback. If it wants to
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set a certificate, a certificate/private key combination must be set
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using the \fBx509\fR and \fBpkey\fR arguments and \*(L"1\*(R" must be returned. The
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certificate will be installed into \fBssl\fR, see the \s-1NOTES\s0 and \s-1BUGS\s0 sections.
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If no certificate should be set, \*(L"0\*(R" has to be returned and no certificate
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will be sent. A negative return value will suspend the handshake and the
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handshake function will return immediatly. \fISSL_get_error\fR\|(3)
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will return \s-1SSL_ERROR_WANT_X509_LOOKUP\s0 to indicate, that the handshake was
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suspended. The next call to the handshake function will again lead to the call
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of \fIclient_cert_cb()\fR. It is the job of the \fIclient_cert_cb()\fR to store information
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about the state of the last call, if required to continue.
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.SH "NOTES"
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.IX Header "NOTES"
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During a handshake (or renegotiation) a server may request a certificate
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from the client. A client certificate must only be sent, when the server
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did send the request.
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.PP
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When a certificate was set using the
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\&\fISSL_CTX_use_certificate\fR\|(3) family of functions,
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it will be sent to the server. The \s-1TLS\s0 standard requires that only a
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certificate is sent, if it matches the list of acceptable CAs sent by the
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server. This constraint is violated by the default behavior of the OpenSSL
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library. Using the callback function it is possible to implement a proper
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selection routine or to allow a user interaction to choose the certificate to
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be sent.
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.PP
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If a callback function is defined and no certificate was yet defined for the
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\&\s-1SSL\s0 object, the callback function will be called.
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If the callback function returns a certificate, the OpenSSL library
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will try to load the private key and certificate data into the \s-1SSL\s0
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object using the \fISSL_use_certificate()\fR and \fISSL_use_private_key()\fR functions.
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Thus it will permanently install the certificate and key for this \s-1SSL\s0
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object. It will not be reset by calling \fISSL_clear\fR\|(3).
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If the callback returns no certificate, the OpenSSL library will not send
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a certificate.
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.SH "BUGS"
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.IX Header "BUGS"
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The \fIclient_cert_cb()\fR cannot return a complete certificate chain, it can
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only return one client certificate. If the chain only has a length of 2,
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the root \s-1CA\s0 certificate may be omitted according to the \s-1TLS\s0 standard and
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thus a standard conforming answer can be sent to the server. For a
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longer chain, the client must send the complete chain (with the option
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to leave out the root \s-1CA\s0 certificate). This can only be accomplished by
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either adding the intermediate \s-1CA\s0 certificates into the trusted
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certificate store for the \s-1SSL_CTX\s0 object (resulting in having to add
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\&\s-1CA\s0 certificates that otherwise maybe would not be trusted), or by adding
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the chain certificates using the
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\&\fISSL_CTX_add_extra_chain_cert\fR\|(3)
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function, which is only available for the \s-1SSL_CTX\s0 object as a whole and that
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therefore probably can only apply for one client certificate, making
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the concept of the callback function (to allow the choice from several
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certificates) questionable.
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.PP
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Once the \s-1SSL\s0 object has been used in conjunction with the callback function,
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the certificate will be set for the \s-1SSL\s0 object and will not be cleared
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even when \fISSL_clear\fR\|(3) is being called. It is therefore
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mandatory to destroy the \s-1SSL\s0 object using \fISSL_free\fR\|(3)
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and create a new one to return to the previous state.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIssl\fR\|(3), \fISSL_CTX_use_certificate\fR\|(3),
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\&\fISSL_CTX_add_extra_chain_cert\fR\|(3),
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\&\fISSL_get_client_CA_list\fR\|(3),
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\&\fISSL_clear\fR\|(3), \fISSL_free\fR\|(3)
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