4746f25ac6
[skip ci] Reviewed-by: Matt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/7829)
358 lines
14 KiB
Text
358 lines
14 KiB
Text
=pod
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=head1 NAME
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SSL_get_ex_data_X509_STORE_CTX_idx,
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SSL_CTX_set_verify, SSL_set_verify,
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SSL_CTX_set_verify_depth, SSL_set_verify_depth,
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SSL_verify_cb,
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SSL_verify_client_post_handshake,
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SSL_set_post_handshake_auth,
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SSL_CTX_set_post_handshake_auth
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- set peer certificate verification parameters
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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typedef int (*SSL_verify_cb)(int preverify_ok, X509_STORE_CTX *x509_ctx);
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void SSL_CTX_set_verify(SSL_CTX *ctx, int mode, SSL_verify_cb verify_callback);
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void SSL_set_verify(SSL *ssl, int mode, SSL_verify_cb verify_callback);
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SSL_get_ex_data_X509_STORE_CTX_idx(void);
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void SSL_CTX_set_verify_depth(SSL_CTX *ctx, int depth);
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void SSL_set_verify_depth(SSL *ssl, int depth);
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int SSL_verify_client_post_handshake(SSL *ssl);
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void SSL_CTX_set_post_handshake_auth(SSL_CTX *ctx, int val);
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void SSL_set_post_handshake_auth(SSL *ssl, int val);
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=head1 DESCRIPTION
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SSL_CTX_set_verify() sets the verification flags for B<ctx> to be B<mode> and
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specifies the B<verify_callback> function to be used. If no callback function
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shall be specified, the NULL pointer can be used for B<verify_callback>.
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SSL_set_verify() sets the verification flags for B<ssl> to be B<mode> and
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specifies the B<verify_callback> function to be used. If no callback function
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shall be specified, the NULL pointer can be used for B<verify_callback>. In
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this case last B<verify_callback> set specifically for this B<ssl> remains. If
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no special B<callback> was set before, the default callback for the underlying
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B<ctx> is used, that was valid at the time B<ssl> was created with
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L<SSL_new(3)>. Within the callback function,
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B<SSL_get_ex_data_X509_STORE_CTX_idx> can be called to get the data index
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of the current SSL object that is doing the verification.
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SSL_CTX_set_verify_depth() sets the maximum B<depth> for the certificate chain
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verification that shall be allowed for B<ctx>.
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SSL_set_verify_depth() sets the maximum B<depth> for the certificate chain
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verification that shall be allowed for B<ssl>.
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SSL_CTX_set_post_handshake_auth() and SSL_set_post_handshake_auth() enable the
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Post-Handshake Authentication extension to be added to the ClientHello such that
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post-handshake authentication can be requested by the server. If B<val> is 0
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then the extension is not sent, otherwise it is. By default the extension is not
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sent. A certificate callback will need to be set via
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SSL_CTX_set_client_cert_cb() if no certificate is provided at initialization.
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SSL_verify_client_post_handshake() causes a CertificateRequest message to be
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sent by a server on the given B<ssl> connection. The SSL_VERIFY_PEER flag must
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be set; the SSL_VERIFY_POST_HANDSHAKE flag is optional.
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=head1 NOTES
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The verification of certificates can be controlled by a set of logically
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or'ed B<mode> flags:
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=over 4
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=item SSL_VERIFY_NONE
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B<Server mode:> the server will not send a client certificate request to the
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client, so the client will not send a certificate.
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B<Client mode:> if not using an anonymous cipher (by default disabled), the
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server will send a certificate which will be checked. The result of the
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certificate verification process can be checked after the TLS/SSL handshake
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using the L<SSL_get_verify_result(3)> function.
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The handshake will be continued regardless of the verification result.
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=item SSL_VERIFY_PEER
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B<Server mode:> the server sends a client certificate request to the client.
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The certificate returned (if any) is checked. If the verification process
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fails, the TLS/SSL handshake is
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immediately terminated with an alert message containing the reason for
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the verification failure.
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The behaviour can be controlled by the additional
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SSL_VERIFY_FAIL_IF_NO_PEER_CERT, SSL_VERIFY_CLIENT_ONCE and
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SSL_VERIFY_POST_HANDSHAKE flags.
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B<Client mode:> the server certificate is verified. If the verification process
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fails, the TLS/SSL handshake is
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immediately terminated with an alert message containing the reason for
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the verification failure. If no server certificate is sent, because an
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anonymous cipher is used, SSL_VERIFY_PEER is ignored.
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=item SSL_VERIFY_FAIL_IF_NO_PEER_CERT
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B<Server mode:> if the client did not return a certificate, the TLS/SSL
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handshake is immediately terminated with a "handshake failure" alert.
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This flag must be used together with SSL_VERIFY_PEER.
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B<Client mode:> ignored
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=item SSL_VERIFY_CLIENT_ONCE
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B<Server mode:> only request a client certificate once during the
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connection. Do not ask for a client certificate again during
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renegotiation or post-authentication if a certificate was requested
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during the initial handshake. This flag must be used together with
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SSL_VERIFY_PEER.
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B<Client mode:> ignored
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=item SSL_VERIFY_POST_HANDSHAKE
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B<Server mode:> the server will not send a client certificate request
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during the initial handshake, but will send the request via
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SSL_verify_client_post_handshake(). This allows the SSL_CTX or SSL
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to be configured for post-handshake peer verification before the
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handshake occurs. This flag must be used together with
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SSL_VERIFY_PEER. TLSv1.3 only; no effect on pre-TLSv1.3 connections.
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B<Client mode:> ignored
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=back
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If the B<mode> is SSL_VERIFY_NONE none of the other flags may be set.
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The actual verification procedure is performed either using the built-in
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verification procedure or using another application provided verification
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function set with
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L<SSL_CTX_set_cert_verify_callback(3)>.
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The following descriptions apply in the case of the built-in procedure. An
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application provided procedure also has access to the verify depth information
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and the verify_callback() function, but the way this information is used
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may be different.
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SSL_CTX_set_verify_depth() and SSL_set_verify_depth() set a limit on the
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number of certificates between the end-entity and trust-anchor certificates.
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Neither the
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end-entity nor the trust-anchor certificates count against B<depth>. If the
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certificate chain needed to reach a trusted issuer is longer than B<depth+2>,
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X509_V_ERR_CERT_CHAIN_TOO_LONG will be issued.
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The depth count is "level 0:peer certificate", "level 1: CA certificate",
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"level 2: higher level CA certificate", and so on. Setting the maximum
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depth to 2 allows the levels 0, 1, 2 and 3 (0 being the end-entity and 3 the
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trust-anchor).
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The default depth limit is 100,
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allowing for the peer certificate, at most 100 intermediate CA certificates and
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a final trust anchor certificate.
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The B<verify_callback> function is used to control the behaviour when the
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SSL_VERIFY_PEER flag is set. It must be supplied by the application and
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receives two arguments: B<preverify_ok> indicates, whether the verification of
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the certificate in question was passed (preverify_ok=1) or not
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(preverify_ok=0). B<x509_ctx> is a pointer to the complete context used
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for the certificate chain verification.
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The certificate chain is checked starting with the deepest nesting level
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(the root CA certificate) and worked upward to the peer's certificate.
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At each level signatures and issuer attributes are checked. Whenever
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a verification error is found, the error number is stored in B<x509_ctx>
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and B<verify_callback> is called with B<preverify_ok>=0. By applying
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X509_CTX_store_* functions B<verify_callback> can locate the certificate
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in question and perform additional steps (see EXAMPLES). If no error is
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found for a certificate, B<verify_callback> is called with B<preverify_ok>=1
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before advancing to the next level.
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The return value of B<verify_callback> controls the strategy of the further
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verification process. If B<verify_callback> returns 0, the verification
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process is immediately stopped with "verification failed" state. If
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SSL_VERIFY_PEER is set, a verification failure alert is sent to the peer and
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the TLS/SSL handshake is terminated. If B<verify_callback> returns 1,
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the verification process is continued. If B<verify_callback> always returns
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1, the TLS/SSL handshake will not be terminated with respect to verification
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failures and the connection will be established. The calling process can
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however retrieve the error code of the last verification error using
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L<SSL_get_verify_result(3)> or by maintaining its
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own error storage managed by B<verify_callback>.
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If no B<verify_callback> is specified, the default callback will be used.
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Its return value is identical to B<preverify_ok>, so that any verification
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failure will lead to a termination of the TLS/SSL handshake with an
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alert message, if SSL_VERIFY_PEER is set.
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After calling SSL_set_post_handshake_auth(), the client will need to add a
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certificate or certificate callback to its configuration before it can
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successfully authenticate. This must be called before SSL_connect().
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SSL_verify_client_post_handshake() requires that verify flags have been
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previously set, and that a client sent the post-handshake authentication
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extension. When the client returns a certificate the verify callback will be
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invoked. A write operation must take place for the Certificate Request to be
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sent to the client, this can be done with SSL_do_handshake() or SSL_write_ex().
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Only one certificate request may be outstanding at any time.
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When post-handshake authentication occurs, a refreshed NewSessionTicket
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message is sent to the client.
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=head1 BUGS
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In client mode, it is not checked whether the SSL_VERIFY_PEER flag
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is set, but whether any flags are set. This can lead to
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unexpected behaviour if SSL_VERIFY_PEER and other flags are not used as
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required.
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=head1 RETURN VALUES
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The SSL*_set_verify*() functions do not provide diagnostic information.
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The SSL_verify_client_post_handshake() function returns 1 if the request
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succeeded, and 0 if the request failed. The error stack can be examined
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to determine the failure reason.
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=head1 EXAMPLES
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The following code sequence realizes an example B<verify_callback> function
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that will always continue the TLS/SSL handshake regardless of verification
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failure, if wished. The callback realizes a verification depth limit with
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more informational output.
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All verification errors are printed; information about the certificate chain
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is printed on request.
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The example is realized for a server that does allow but not require client
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certificates.
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The example makes use of the ex_data technique to store application data
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into/retrieve application data from the SSL structure
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(see L<CRYPTO_get_ex_new_index(3)>,
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L<SSL_get_ex_data_X509_STORE_CTX_idx(3)>).
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...
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typedef struct {
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int verbose_mode;
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int verify_depth;
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int always_continue;
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} mydata_t;
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int mydata_index;
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...
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static int verify_callback(int preverify_ok, X509_STORE_CTX *ctx)
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{
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char buf[256];
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X509 *err_cert;
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int err, depth;
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SSL *ssl;
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mydata_t *mydata;
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err_cert = X509_STORE_CTX_get_current_cert(ctx);
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err = X509_STORE_CTX_get_error(ctx);
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depth = X509_STORE_CTX_get_error_depth(ctx);
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/*
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* Retrieve the pointer to the SSL of the connection currently treated
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* and the application specific data stored into the SSL object.
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*/
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ssl = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
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mydata = SSL_get_ex_data(ssl, mydata_index);
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X509_NAME_oneline(X509_get_subject_name(err_cert), buf, 256);
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/*
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* Catch a too long certificate chain. The depth limit set using
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* SSL_CTX_set_verify_depth() is by purpose set to "limit+1" so
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* that whenever the "depth>verify_depth" condition is met, we
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* have violated the limit and want to log this error condition.
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* We must do it here, because the CHAIN_TOO_LONG error would not
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* be found explicitly; only errors introduced by cutting off the
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* additional certificates would be logged.
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*/
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if (depth > mydata->verify_depth) {
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preverify_ok = 0;
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err = X509_V_ERR_CERT_CHAIN_TOO_LONG;
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X509_STORE_CTX_set_error(ctx, err);
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}
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if (!preverify_ok) {
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printf("verify error:num=%d:%s:depth=%d:%s\n", err,
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X509_verify_cert_error_string(err), depth, buf);
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} else if (mydata->verbose_mode) {
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printf("depth=%d:%s\n", depth, buf);
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}
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/*
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* At this point, err contains the last verification error. We can use
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* it for something special
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*/
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if (!preverify_ok && (err == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT)) {
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X509_NAME_oneline(X509_get_issuer_name(err_cert), buf, 256);
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printf("issuer= %s\n", buf);
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}
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if (mydata->always_continue)
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return 1;
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else
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return preverify_ok;
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}
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...
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mydata_t mydata;
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...
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mydata_index = SSL_get_ex_new_index(0, "mydata index", NULL, NULL, NULL);
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...
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SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE,
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verify_callback);
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/*
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* Let the verify_callback catch the verify_depth error so that we get
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* an appropriate error in the logfile.
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*/
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SSL_CTX_set_verify_depth(verify_depth + 1);
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/*
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* Set up the SSL specific data into "mydata" and store it into th SSL
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* structure.
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*/
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mydata.verify_depth = verify_depth; ...
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SSL_set_ex_data(ssl, mydata_index, &mydata);
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...
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SSL_accept(ssl); /* check of success left out for clarity */
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if (peer = SSL_get_peer_certificate(ssl)) {
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if (SSL_get_verify_result(ssl) == X509_V_OK) {
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/* The client sent a certificate which verified OK */
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}
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}
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=head1 SEE ALSO
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L<ssl(7)>, L<SSL_new(3)>,
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L<SSL_CTX_get_verify_mode(3)>,
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L<SSL_get_verify_result(3)>,
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L<SSL_CTX_load_verify_locations(3)>,
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L<SSL_get_peer_certificate(3)>,
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L<SSL_CTX_set_cert_verify_callback(3)>,
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L<SSL_get_ex_data_X509_STORE_CTX_idx(3)>,
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L<SSL_CTX_set_client_cert_cb(3)>,
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L<CRYPTO_get_ex_new_index(3)>
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=head1 HISTORY
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The SSL_VERIFY_POST_HANDSHAKE option, and the SSL_verify_client_post_handshake()
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and SSL_set_post_handshake_auth() functions were added in OpenSSL 1.1.1.
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=head1 COPYRIGHT
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Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). 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 LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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