OpenSSL SSL_CTX_set_verify(3openssl)
NNNNAAAAMMMMEEEESSL_CTX_set_verify, SSL_set_verify,
SSL_CTX_set_verify_depth, SSL_set_verify_depth - set peer
certificate verification parameters SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS#include
void SSL_CTX_set_verify(SSL_CTX *ctx, int mode,
int (*verify_callback)(int, X509_STORE_CTX *));
void SSL_set_verify(SSL *s, int mode,
int (*verify_callback)(int, X509_STORE_CTX *));
void SSL_CTX_set_verify_depth(SSL_CTX *ctx,int depth);
void SSL_set_verify_depth(SSL *s, int depth);
int verify_callback(int preverify_ok, X509_STORE_CTX *x509_ctx);
DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNNSSL_CTX_set_verify() sets the verification flags for ccccttttxxxx to
be mmmmooooddddeeee and specifies the vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk function to be
used. If no callback function shall be specified, the NULLpointer can be used for vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk.
SSL_set_verify() sets the verification flags for ssssssssllll to be
mmmmooooddddeeee and specifies the vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk function to be used.
If no callback function shall be specified, the NULL pointercan be used for vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk. In this case last
vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk set specifically for this ssssssssllll remains. If no
special ccccaaaallllllllbbbbaaaacccckkkk was set before, the default callback for the underlying ccccttttxxxx is used, that was valid at the time ssssssssllllwas created with SSL_new(3).
SSL_CTX_set_verify_depth() sets the maximum ddddeeeepppptttthhhh for the
certificate chain verification that shall be allowed forccccttttxxxx. (See the BUGS section.)
SSL_set_verify_depth() sets the maximum ddddeeeepppptttthhhh for the
certificate chain verification that shall be allowed forssssssssllll. (See the BUGS section.)
NNNNOOOOTTTTEEEESSSS The verification of certificates can be controlled by a set of logically or'ed mmmmooooddddeeee flags:SSL_VERIFY_NONE
SSSSeeeerrrrvvvveeeerrrr mmmmooooddddeeee:::: the server will not send a client certificate request to the client, so the client will not send a certificate. CCCClllliiiieeeennnntttt mmmmooooddddeeee:::: if not using an anonymous cipher (by default disabled), the server will send a certificate14/Feb/2009 Last change: 0.9.8o 1
OpenSSL SSL_CTX_set_verify(3openssl)
which will be checked. The result of the certificateverification process can be checked after the TLS/SSL
handshake using the SSL_get_verify_result(3) function.
The handshake will be continued regardless of the verification result.SSL_VERIFY_PEER
SSSSeeeerrrrvvvveeeerrrr mmmmooooddddeeee:::: the server sends a client certificate request to the client. The certificate returned (if any) is checked. If the verification process fails, theTLS/SSL handshake is immediately terminated with an alert message containing the reason for the verification failure. The behaviour can be controlled by the
additional SSL_VERIFY_FAIL_IF_NO_PEER_CERT and
SSL_VERIFY_CLIENT_ONCE flags.
CCCClllliiiieeeennnntttt mmmmooooddddeeee:::: the server certificate is verified. If theverification process fails, the TLS/SSL handshake is immediately terminated with an alert message containing the reason for the verification failure. If no server certificate is sent, because an anonymous cipher is
used, SSL_VERIFY_PEER is ignored.
SSL_VERIFY_FAIL_IF_NO_PEER_CERT
SSSSeeeerrrrvvvveeeerrrr mmmmooooddddeeee:::: if the client did not return a certificate,the TLS/SSL handshake is immediately terminated with a "handshake failure" alert. This flag must be used
together with SSL_VERIFY_PEER.
CCCClllliiiieeeennnntttt mmmmooooddddeeee:::: ignoredSSL_VERIFY_CLIENT_ONCE
SSSSeeeerrrrvvvveeeerrrr mmmmooooddddeeee:::: only request a client certificate on theinitial TLS/SSL handshake. Do not ask for a client certificate again in case of a renegotiation. This flag
must be used together with SSL_VERIFY_PEER.
CCCClllliiiieeeennnntttt mmmmooooddddeeee:::: ignoredExactly one of the mmmmooooddddeeee flags SSL_VERIFY_NONE and
SSL_VERIFY_PEER must be set at any time.
The actual verification procedure is performed either usingthe built-in verification procedure or using another
application provided verification function set withSSL_CTX_set_cert_verify_callback(3). The following
descriptions apply in the case of the built-in procedure. An
application provided procedure also has access to the verifydepth information and the verify_callback() function, but
the way this information is used may be different.14/Feb/2009 Last change: 0.9.8o 2
OpenSSL SSL_CTX_set_verify(3openssl)
SSL_CTX_set_verify_depth() and SSL_set_verify_depth() set
the limit up to which depth certificates in a chain are used during the verification procedure. If the certificate chain is longer than allowed, the certificates above the limit are ignored. Error messages are generated as if these certificates would not be present, most likely aX509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY will be issued.
The depth count is "level 0:peer certificate", "level 1: CA certificate", "level 2: higher level CA certificate", and so on. Setting the maximum depth to 2 allows the levels 0, 1, and 2. The default depth limit is 9, allowing for the peer certificate and additional 9 CA certificates.The vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk function is used to control the
behaviour when the SSL_VERIFY_PEER flag is set. It must be
supplied by the application and receives two arguments:pppprrrreeeevvvveeeerrrriiiiffffyyyy_ooookkkk indicates, whether the verification of the
certificate in question was passed (preverify_ok=1) or not
(preverify_ok=0). xxxx555500009999_ccccttttxxxx is a pointer to the complete
context used for the certificate chain verification. The certificate chain is checked starting with the deepest nesting level (the root CA certificate) and worked upward to the peer's certificate. At each level signatures and issuer attributes are checked. Whenever a verification error isfound, the error number is stored in xxxx555500009999_ccccttttxxxx and
vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk is called with pppprrrreeeevvvveeeerrrriiiiffffyyyy_ooookkkk=0. By applying
X509_CTX_store_* functions vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk can locate the
certificate in question and perform additional steps (seeEXAMPLES). If no error is found for a certificate,
vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk is called with pppprrrreeeevvvveeeerrrriiiiffffyyyy_ooookkkk=1 before
advancing to the next level.The return value of vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk controls the strategy of
the further verification process. If vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk returns
0, the verification process is immediately stopped with"verification failed" state. If SSL_VERIFY_PEER is set, a
verification failure alert is sent to the peer and theTLS/SSL handshake is terminated. If vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk returns
1, the verification process is continued. If vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk
always returns 1, the TLS/SSL handshake will not be terminated with respect to verification failures and the connection will be established. The calling process can however retrieve the error code of the last verification
error using SSL_get_verify_result(3) or by maintaining its
own error storage managed by vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk.
If no vvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk is specified, the default callback
will be used. Its return value is identical topppprrrreeeevvvveeeerrrriiiiffffyyyy_ooookkkk, so that any verification failure will lead to
a termination of the TLS/SSL handshake with an alert
message, if SSL_VERIFY_PEER is set.
14/Feb/2009 Last change: 0.9.8o 3
OpenSSL SSL_CTX_set_verify(3openssl)
BBBBUUUUGGGGSSSS In client mode, it is not checked whether theSSL_VERIFY_PEER flag is set, but whether SSL_VERIFY_NONE is
not set. This can lead to unexpected behaviour, if theSSL_VERIFY_PEER and SSL_VERIFY_NONE are not used as required
(exactly one must be set at any time). The certificate verification depth set withSSL[_CTX]_verify_depth() stops the verification at a certain
depth. The error message produced will be that of an incomplete certificate chain and notX509_V_ERR_CERT_CHAIN_TOO_LONG as may be expected.
RRRREEEETTTTUUUURRRRNNNN VVVVAAAALLLLUUUUEEEESSSSThe SSL*_set_verify*() functions do not provide diagnostic
information. EEEEXXXXAAAAMMMMPPPPLLLLEEEESSSS The following code sequence realizes an examplevvvveeeerrrriiiiffffyyyy_ccccaaaallllllllbbbbaaaacccckkkk function that will always continue the
TLS/SSL handshake regardless of verification failure, if wished. The callback realizes a verification depth limit with more informational output. All verification errors are printed, informations about the certificate chain are printed on request. The example is realized for a server that does allow but not require client certificates.
The example makes use of the ex_data technique to store
application data into/retrieve application data from the SSLstructure (see SSL_get_ex_new_index(3),
SSL_get_ex_data_X509_STORE_CTX_idx(3)).
... typedef struct {int verbose_mode;
int verify_depth;
int always_continue;
} mydata_t;
int mydata_index;
...static int verify_callback(int preverify_ok, X509_STORE_CTX *ctx)
{ char buf[256];X509 *err_cert;
int err, depth; SSL *ssl;mydata_t *mydata;
14/Feb/2009 Last change: 0.9.8o 4
OpenSSL SSL_CTX_set_verify(3openssl)
err_cert = X509_STORE_CTX_get_current_cert(ctx);
err = X509_STORE_CTX_get_error(ctx);
depth = X509_STORE_CTX_get_error_depth(ctx);
/* * Retrieve the pointer to the SSL of the connection currently treated * and the application specific data stored into the SSL object. */ssl = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
mydata = SSL_get_ex_data(ssl, mydata_index);
X509_NAME_oneline(X509_get_subject_name(err_cert), buf, 256);
/* * Catch a too long certificate chain. The depth limit set using* SSL_CTX_set_verify_depth() is by purpose set to "limit+1" so
* that whenever the "depth>verify_depth" condition is met, we
* have violated the limit and want to log this error condition.* We must do it here, because the CHAIN_TOO_LONG error would not
* be found explicitly; only errors introduced by cutting off the * additional certificates would be logged. */if (depth > mydata->verify_depth) {
preverify_ok = 0;
err = X509_V_ERR_CERT_CHAIN_TOO_LONG;
X509_STORE_CTX_set_error(ctx, err);
}if (!preverify_ok) {
printf("verify error:num=%d:%s:depth=%d:%s\n", err,
X509_verify_cert_error_string(err), depth, buf);
}else if (mydata->verbose_mode)
{printf("depth=%d:%s\n", depth, buf);
} /* * At this point, err contains the last verification error. We can use * it for something special */if (!preverify_ok && (err == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT))
{X509_NAME_oneline(X509_get_issuer_name(ctx->current_cert), buf, 256);
printf("issuer= %s\n", buf);
}if (mydata->always_continue)
return 1; elsereturn preverify_ok;
} ...14/Feb/2009 Last change: 0.9.8o 5
OpenSSL SSL_CTX_set_verify(3openssl)
mydata_t mydata;
...mydata_index = SSL_get_ex_new_index(0, "mydata index", NULL, NULL, NULL);
...SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER|SSL_VERIFY_CLIENT_ONCE,
verify_callback);
/** Let the verify_callback catch the verify_depth error so that we get
* an appropriate error in the logfile. */SSL_CTX_set_verify_depth(verify_depth + 1);
/* * Set up the SSL specific data into "mydata" and store it into th SSL * structure. */mydata.verify_depth = verify_depth; ...
SSL_set_ex_data(ssl, mydata_index, &mydata);
...SSL_accept(ssl); /* check of success left out for clarity */
if (peer = SSL_get_peer_certificate(ssl))
{if (SSL_get_verify_result(ssl) == X509_V_OK)
{ /* The client sent a certificate which verified OK */ } } SSSSEEEEEEEE AAAALLLLSSSSOOOOssl(3), SSL_new(3), SSL_CTX_get_verify_mode(3),
SSL_get_verify_result(3), SSL_CTX_load_verify_locations(3),
SSL_get_peer_certificate(3),
SSL_CTX_set_cert_verify_callback(3),
SSL_get_ex_data_X509_STORE_CTX_idx(3),
SSL_get_ex_new_index(3)
14/Feb/2009 Last change: 0.9.8o 6
OpenSSL SSL_CTX_set_verify(3openssl)
14/Feb/2009 Last change: 0.9.8o 7