RETURN VALUES
X509_VERIFY_PARAM_set_flags(), X509_VERIFY_PARAM_clear_flags(), X509_VERIFY_PARAM_set_inh_flags(), X509_VERIFY_PARAM_set_purpose(), X509_VERIFY_PARAM_set_trust(), X509_VERIFY_PARAM_add0_policy() X509_VERIFY_PARAM_set1_policies(), X509_VERIFY_PARAM_set1_host(), X509_VERIFY_PARAM_add1_host(), X509_VERIFY_PARAM_set1_email(), X509_VERIFY_PARAM_set1_ip() and X509_VERIFY_PARAM_set1_ip_asc() return 1 for success and 0 for failure.
X509_VERIFY_PARAM_get_flags() returns the current verification flags.
X509_VERIFY_PARAM_get_hostflags() returns any current host flags.
X509_VERIFY_PARAM_get_inh_flags() returns the current inheritance 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.
X509_VERIFY_PARAM_get_auth_level() returns the current authentication security level.
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 performed. 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 is 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 certificate 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.
When X509_V_FLAG_TRUSTED_FIRST is set, construction of the certificate chain in x509(1)). As of OpenSSL 1.1.0 this option is on by default.
The X509_V_FLAG_NO_ALT_CHAINS flag suppresses checking for alternative chains. By default, unless X509_V_FLAG_TRUSTED_FIRST is set, when building a certificate chain, if the first certificate chain found is not trusted, then OpenSSL will attempt to replace untrusted certificates supplied by the peer with certificates from the trust store to see if an alternative chain can be found that is trusted. As of OpenSSL 1.1.0, with X509_V_FLAG_TRUSTED_FIRST always set, this option has no effect.
The X509_V_FLAG_PARTIAL_CHAIN flag causes intermediate certificates in the trust store to be treated as trust-anchors, in the same way as the self-signed root CA certificates. This makes it possible to trust certificates issued by an intermediate CA without having to trust its ancestor root CA. With OpenSSL 1.1.0 and later and <X509_V_FLAG_PARTIAL_CHAIN> set, chain construction stops as soon as the first certificate from the trust store is added to the chain, whether that certificate is a self-signed "root" certificate or a not self-signed intermediate certificate. Thus, when an intermediate certificate is found in the trust store, the verified chain passed to callbacks may be shorter than it otherwise would be without the X509_V_FLAG_PARTIAL_CHAIN flag.
The X509_V_FLAG_NO_CHECK_TIME flag suppresses checking the validity period of certificates and CRLs against the current time. If X509_VERIFY_PARAM_set_time() is used to specify a verification time, the check is not suppressed.
INHERITANCE FLAGS
These flags specify how parameters are "inherited" from one structure to another.
If X509_VP_FLAG_ONCE is set then the current setting is zeroed after the next call.
If X509_VP_FLAG_LOCKED is set then no values are copied. This overrides all of the following flags.
If X509_VP_FLAG_DEFAULT is set then anything set in the source is copied to the destination. Effectively the values in "to" become default values which will be used only if nothing new is set in "from". This is the default.
If X509_VP_FLAG_OVERWRITE is set then all value are copied across whether they are set or not. Flags is still Ored though.
If X509_VP_FLAG_RESET_FLAGS is set then the flags value is copied instead of ORed.
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_check_host(3), X509_check_ip(3), HISTORY
The X509_V_FLAG_NO_ALT_CHAINS flag was added in OpenSSL 1.1.0 The legacy X509_V_FLAG_CB_ISSUER_CHECK flag is deprecated as of OpenSSL 1.1.0, and has no effect.
X509_VERIFY_PARAM_get_hostflags() was added in OpenSSL 1.1.0i.
COPYRIGHT
Copyright 2009-2018 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at https://www.openssl.org/source/license.html.