DESCRIPTION

These functions manipulate the X509_VERIFY_PARAM structure associated with a certificate verification operation.

The X509_VERIFY_PARAM_set_flags() function sets the flags in param by oring it with flags. See the VERIFICATION FLAGS section for a complete description of values the flags parameter can take.

X509_VERIFY_PARAM_get_flags() returns the flags in param.

X509_VERIFY_PARAM_clear_flags() clears the flags flags in param.

X509_VERIFY_PARAM_set_purpose() sets the verification purpose in param to purpose. This determines the acceptable purpose of the certificate chain, for example SSL client or SSL server.

X509_VERIFY_PARAM_set_trust() sets the trust setting in param to trust.

X509_VERIFY_PARAM_set_time() sets the verification time in param to t. Normally the current time is used.

X509_VERIFY_PARAM_add0_policy() enables policy checking (it is disabled by default) and adds policy to the acceptable policy set.

X509_VERIFY_PARAM_set1_policies() enables policy checking (it is disabled by default) and sets the acceptable policy set to policies. Any existing policy set is cleared. The policies parameter can be NULL to clear an existing policy set.

X509_VERIFY_PARAM_set_depth() sets the maximum verification depth to depth. That is the maximum number of untrusted CA certificates that can appear in a chain.

RETURN VALUES

X509_VERIFY_PARAM_set_flags(), X509_VERIFY_PARAM_clear_flags(), X509_VERIFY_PARAM_set_purpose(), X509_VERIFY_PARAM_set_trust(), X509_VERIFY_PARAM_add0_policy() and X509_VERIFY_PARAM_set1_policies() return 1 for success and 0 for failure.

X509_VERIFY_PARAM_get_flags() returns the current verification flags.

X509_VERIFY_PARAM_set_time() and X509_VERIFY_PARAM_set_depth() do not return values.

X509_VERIFY_PARAM_get_depth() returns the current verification depth.

VERIFICATION FLAGS

The verification flags consists of zero or more of the following flags ored together.

X509_V_FLAG_CRL_CHECK enables CRL checking for the certificate chain leaf certificate. An error occurs if a suitable CRL cannot be found.

X509_V_FLAG_CRL_CHECK_ALL enables CRL checking for the entire certificate chain.

X509_V_FLAG_IGNORE_CRITICAL disabled critical extension checking. By default any unhandled critical extensions in certificates or (if checked) CRLs results in a fatal error. If this flag is set unhandled critical extensions are ignored. WARNING setting this option for anything other than debugging purposes can be a security risk. Finer control over which extensions are supported can be performed in the verification callback.

THe X509_V_FLAG_X509_STRICT flag disables workarounds for some broken certificates and makes the verification strictly apply X509 rules.

X509_V_FLAG_ALLOW_PROXY_CERTS enables proxy certificate verification.

X509_V_FLAG_POLICY_CHECK enables certificate policy checking, by default no policy checking is peformed. Additional information is sent to the verification callback relating to policy checking.

X509_V_FLAG_EXPLICIT_POLICY, X509_V_FLAG_INHIBIT_ANY and X509_V_FLAG_INHIBIT_MAP set the require explicit policy, inhibit any policy and inhibit policy mapping flags respectively as defined in RFC3280. Policy checking is automatically enabled if any of these flags are set.

If X509_V_FLAG_NOTIFY_POLICY is set and the policy checking is successful a special status code is set to the verification callback. This permits it to examine the valid policy tree and perform additional checks or simply log it for debugging purposes.

By default some additional features such as indirect CRLs and CRLs signed by different keys are disabled. If X509_V_FLAG_EXTENDED_CRL_SUPPORT is set they are enabled.

If X509_V_FLAG_USE_DELTAS ise set delta CRLs (if present) are used to determine certificate status. If not set deltas are ignored.

X509_V_FLAG_CHECK_SS_SIGNATURE enables checking of the root CA self signed cerificate signature. By default this check is disabled because it doesn't add any additional security but in some cases applications might want to check the signature anyway. A side effect of not checking the root CA signature is that disabled or unsupported message digests on the root CA are not treated as fatal errors.

The X509_V_FLAG_CB_ISSUER_CHECK flag enables debugging of certificate issuer checks. It is not needed unless you are logging certificate verification. If this flag is set then additional status codes will be sent to the verification callback and it must be prepared to handle such cases without assuming they are hard errors.

The X509_V_FLAG_NO_ALT_CHAINS flag suppresses checking for alternative chains. By default, when building a certificate chain, if the first certificate chain found is not trusted, then OpenSSL will continue to check to see if an alternative chain can be found that is trusted. With this flag set the behaviour will match that of OpenSSL versions prior to 1.0.1n and 1.0.2b.

NOTES

The above functions should be used to manipulate verification parameters instead of legacy functions which work in specific structures such as X509_STORE_CTX_set_flags().

BUGS

Delta CRL checking is currently primitive. Only a single delta can be used and (partly due to limitations of X509_STORE) constructed CRLs are not maintained.

If CRLs checking is enable CRLs are expected to be available in the corresponding X509_STORE structure. No attempt is made to download CRLs from the CRL distribution points extension.

EXAMPLE

Enable CRL checking when performing certificate verification during SSL connections associated with an SSL_CTX structure ctx:

X509_VERIFY_PARAM *param;
param = X509_VERIFY_PARAM_new();
X509_VERIFY_PARAM_set_flags(param, X509_V_FLAG_CRL_CHECK);
SSL_CTX_set1_param(ctx, param);
X509_VERIFY_PARAM_free(param);

SEE ALSO

X509_verify_cert(3)

HISTORY

The X509_V_FLAG_NO_ALT_CHAINS flag was added in OpenSSL 1.0.1n and 1.0.2b