230 lines
8.2 KiB
Groff
230 lines
8.2 KiB
Groff
.\" $NetBSD: SSL_CTX_set_client_cert_cb.3,v 1.4 2002/08/09 16:15:41 itojun 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 "0.9.6g" "2002-08-05" "OpenSSL"
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.UC
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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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.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.
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When \fB\f(BIclient_cert_cb()\fB\fR is \s-1NULL\s0, not 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 the default
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certificate will be sent. A fatal error can be indicated by returning
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a negative value, in which case the handshake will be canceled.
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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 no callback function is set, an OpenSSL client will send the certificate
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that was set using the
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SSL_CTX_use_certificate(3) family of functions.
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The \s-1TLS\s0 standard requires that only a certificate is sent, if it matches
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the list of acceptable CAs sent by the server. This constraint is
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violated by the default behavior of the OpenSSL library. Using the
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callback function it is possible to implement a proper selection routine
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or to allow a user interaction to choose the certificate to be sent.
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The callback function can obtain the list of acceptable CAs using the
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SSL_get_client_CA_list(3) function.
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.PP
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If a callback function is defined, 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 \fISSL_use_certificate()\fR and \fISSL_use_private_key()\fR functions.
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Thus it will permanently override the certificate and key previously
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installed and will not be reset by calling SSL_clear(3).
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If the callback returns no certificate, the OpenSSL library will send
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the certificate previously installed for the \s-1SSL_CTX\s0 object or the specific
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certificate of the \s-1SSL\s0 object, if available.
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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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SSL_CTX_add_extra_chain_cert(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 SSL_clear(3) is being called. It is therefore
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mandatory to destroy the \s-1SSL\s0 object using SSL_free(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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ssl(3), SSL_CTX_use_certificate(3),
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SSL_CTX_add_extra_chain_cert(3),
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SSL_get_client_CA_list(3),
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SSL_clear(3), SSL_free(3)
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