- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- VERIFICATION FLAGS
- INHERITANCE FLAGS
- NOTES
- BUGS
- EXAMPLES
- SEE ALSO
- HISTORY
- COPYRIGHT

# NAME

X509_VERIFY_PARAM_set_flags, X509_VERIFY_PARAM_clear_flags, X509_VERIFY_PARAM_get_flags, X509_VERIFY_PARAM_set_purpose, X509_VERIFY_PARAM_get_purpose, X509_VERIFY_PARAM_get_inh_flags, X509_VERIFY_PARAM_set_inh_flags, X509_VERIFY_PARAM_set_trust, X509_VERIFY_PARAM_set_depth, X509_VERIFY_PARAM_get_depth, X509_VERIFY_PARAM_set_auth_level, X509_VERIFY_PARAM_get_auth_level, X509_VERIFY_PARAM_set_time, X509_VERIFY_PARAM_get_time, X509_VERIFY_PARAM_add0_policy, X509_VERIFY_PARAM_set1_policies, X509_VERIFY_PARAM_get0_host, X509_VERIFY_PARAM_set1_host, X509_VERIFY_PARAM_add1_host, X509_VERIFY_PARAM_set_hostflags, X509_VERIFY_PARAM_get_hostflags, X509_VERIFY_PARAM_get0_peername, X509_VERIFY_PARAM_get0_email, X509_VERIFY_PARAM_set1_email, X509_VERIFY_PARAM_set1_ip, X509_VERIFY_PARAM_get1_ip_asc, X509_VERIFY_PARAM_set1_ip_asc - X509 verification parameters

# SYNOPSIS

     #include <openssl/x509_vfy.h>

     int X509_VERIFY_PARAM_set_flags(X509_VERIFY_PARAM *param,
                                     unsigned long flags);
     int X509_VERIFY_PARAM_clear_flags(X509_VERIFY_PARAM *param,
                                       unsigned long flags);
     unsigned long X509_VERIFY_PARAM_get_flags(const X509_VERIFY_PARAM *param);

     int X509_VERIFY_PARAM_set_inh_flags(X509_VERIFY_PARAM *param,
                                         uint32_t flags);
     uint32_t X509_VERIFY_PARAM_get_inh_flags(const X509_VERIFY_PARAM *param);

     int X509_VERIFY_PARAM_set_purpose(X509_VERIFY_PARAM *param, int purpose);
     int X509_VERIFY_PARAM_get_purpose(X509_VERIFY_PARAM *param);
     int X509_VERIFY_PARAM_set_trust(X509_VERIFY_PARAM *param, int trust);

     void X509_VERIFY_PARAM_set_time(X509_VERIFY_PARAM *param, time_t t);
     time_t X509_VERIFY_PARAM_get_time(const X509_VERIFY_PARAM *param);

     int X509_VERIFY_PARAM_add0_policy(X509_VERIFY_PARAM *param,
                                       ASN1_OBJECT *policy);
     int X509_VERIFY_PARAM_set1_policies(X509_VERIFY_PARAM *param,
                                         STACK_OF(ASN1_OBJECT) *policies);

     void X509_VERIFY_PARAM_set_depth(X509_VERIFY_PARAM *param, int depth);
     int X509_VERIFY_PARAM_get_depth(const X509_VERIFY_PARAM *param);

     void X509_VERIFY_PARAM_set_auth_level(X509_VERIFY_PARAM *param,
                                           int auth_level);
     int X509_VERIFY_PARAM_get_auth_level(const X509_VERIFY_PARAM *param);

     char *X509_VERIFY_PARAM_get0_host(X509_VERIFY_PARAM *param, int n);
     int X509_VERIFY_PARAM_set1_host(X509_VERIFY_PARAM *param,
                                     const char *name, size_t namelen);
     int X509_VERIFY_PARAM_add1_host(X509_VERIFY_PARAM *param,
                                     const char *name, size_t namelen);
     void X509_VERIFY_PARAM_set_hostflags(X509_VERIFY_PARAM *param,
                                          unsigned int flags);
     unsigned int X509_VERIFY_PARAM_get_hostflags(const X509_VERIFY_PARAM *param);
     char *X509_VERIFY_PARAM_get0_peername(const X509_VERIFY_PARAM *param);
     char *X509_VERIFY_PARAM_get0_email(X509_VERIFY_PARAM *param);
     int X509_VERIFY_PARAM_set1_email(X509_VERIFY_PARAM *param,
                                      const char *email, size_t emaillen);
     char *X509_VERIFY_PARAM_get1_ip_asc(X509_VERIFY_PARAM *param);
     int X509_VERIFY_PARAM_set1_ip(X509_VERIFY_PARAM *param,
                                   const unsigned char *ip, size_t iplen);
     int X509_VERIFY_PARAM_set1_ip_asc(X509_VERIFY_PARAM *param, const char *ipasc);

# 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 VERIFICATION FLAGS for a complete description of values the flags parameter can take.

X509_VERIFY_PARAM_get_flags() returns the flags in param.

X509_VERIFY_PARAM_get_inh_flags() returns the inheritance flags in param which specifies how verification flags are copied from one structure to another. X509_VERIFY_PARAM_set_inh_flags() sets the inheritance flags. See the INHERITANCE FLAGS section for a description of these bits.

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 X509_PURPOSE_SSL_CLIENT. The purpose requirement is cleared if purpose is X509_PURPOSE_DEFAULT_ANY.

X509_VERIFY_PARAM_get_purpose() returns the purpose in param.

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() adds policy to the acceptable policy set. Contrary to preexisting documentation of this function it does not enable policy checking.

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 intermediate CA certificates that can appear in a chain. A maximal depth chain contains 2 more certificates than the limit, since neither the end-entity certificate nor the trust-anchor count against this limit. Thus a depth limit of 0 only allows the end-entity certificate to be signed directly by the trust anchor, while with a depth limit of 1 there can be one intermediate CA certificate between the trust anchor and the end-entity certificate.

X509_VERIFY_PARAM_set_auth_level() sets the authentication security level to auth_level. The authentication security level determines the acceptable signature and public key strength when verifying certificate chains. For a certificate chain to validate, the public keys of all the certificates must meet the specified security level. The signature algorithm security level is not enforced for the chain's trust anchor certificate, which is either directly trusted or validated by means other than its signature. See SSL_CTX_set_security_level(3) for the definitions of the available levels. The default security level is -1, or "not set". At security level 0 or lower all algorithms are acceptable. Security level 1 requires at least 80-bit-equivalent security and is broadly interoperable, though it will, for example, reject MD5 signatures or RSA keys shorter than 1024 bits.

X509_VERIFY_PARAM_get0_host() returns the nth expected DNS hostname that has been set using X509_VERIFY_PARAM_set1_host() or X509_VERIFY_PARAM_add1_host(). To obtain all names start with n = 0 and increment n as long as no NULL pointer is returned.

X509_VERIFY_PARAM_set1_host() sets the expected DNS hostname to name clearing any previously specified hostname. If name is NULL, or empty the list of hostnames is cleared, and name checks are not performed on the peer certificate. If name is NUL-terminated, namelen may be zero, otherwise namelen must be set to the length of name.

When a hostname is specified, certificate verification automatically invokes X509_check_host(3) with flags equal to the flags argument given to X509_VERIFY_PARAM_set_hostflags() (default zero). Applications are strongly advised to use this interface in preference to explicitly calling X509_check_host(3), hostname checks may be out of scope with the DANE-EE(3) certificate usage, and the internal check will be suppressed as appropriate when DANE verification is enabled.

When the subject CommonName will not be ignored, whether as a result of the X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT host flag, or because no DNS subject alternative names are present in the certificate, any DNS name constraints in issuer certificates apply to the subject CommonName as well as the subject alternative name extension.

When the subject CommonName will be ignored, whether as a result of the X509_CHECK_FLAG_NEVER_CHECK_SUBJECT host flag, or because some DNS subject alternative names are present in the certificate, DNS name constraints in issuer certificates will not be applied to the subject DN. As described in X509_check_host(3) the X509_CHECK_FLAG_NEVER_CHECK_SUBJECT flag takes precedence over the X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT flag.

X509_VERIFY_PARAM_get_hostflags() returns any host flags previously set via a call to X509_VERIFY_PARAM_set_hostflags().

X509_VERIFY_PARAM_add1_host() adds name as an additional reference identifier that can match the peer's certificate. Any previous names set via X509_VERIFY_PARAM_set1_host() or X509_VERIFY_PARAM_add1_host() are retained, no change is made if name is NULL or empty. When multiple names are configured, the peer is considered verified when any name matches.

X509_VERIFY_PARAM_get0_peername() returns the DNS hostname or subject CommonName from the peer certificate that matched one of the reference identifiers. When wildcard matching is not disabled, or when a reference identifier specifies a parent domain (starts with ".") rather than a hostname, the peer name may be a wildcard name or a sub-domain of the reference identifier respectively. The return string is allocated by the library and is no longer valid once the associated param argument is freed. Applications must not free the return value.

X509_VERIFY_PARAM_get0_email() returns the expected RFC822 email address.

X509_VERIFY_PARAM_set1_email() sets the expected RFC822 email address to email. If email is NUL-terminated, emaillen may be zero, otherwise emaillen must be set to the length of email. When an email address is specified, certificate verification automatically invokes X509_check_email(3).

X509_VERIFY_PARAM_get1_ip_asc() returns the expected IP address as a string. The caller is responsible for freeing it.

X509_VERIFY_PARAM_set1_ip() sets the expected IP address to ip. The ip argument is in binary format, in network byte-order and iplen must be set to 4 for IPv4 and 16 for IPv6. When an IP address is specified, certificate verification automatically invokes X509_check_ip(3).

X509_VERIFY_PARAM_set1_ip_asc() sets the expected IP address to ipasc. The ipasc argument is a NUL-terminal ASCII string: dotted decimal quad for IPv4 and colon-separated hexadecimal for IPv6. The condensed "::" notation is supported for IPv6 addresses.

# 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_get0_host(), X509_VERIFY_PARAM_get0_email(), and X509_VERIFY_PARAM_get1_ip_asc(), return the string pointers specified above or NULL if the respective value has not been set or on error.

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.

X509_VERIFY_PARAM_get_purpose() returns the current purpose, which may be X509_PURPOSE_DEFAULT_ANY if unset.

# 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 expands CRL checking to the entire certificate chain if X509_V_FLAG_CRL_CHECK has also been enabled, and is otherwise ignored.

X509_V_FLAG_IGNORE_CRITICAL disables critical extension checking. By default any unhandled critical extensions in certificates or (if checked) CRLs result 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 requests checking the signature of the last certificate in a chain if the certificate is supposedly self-signed. This is prohibited and will result in an error if it is a non-conforming CA certificate with key usage restrictions not including the keyCertSign bit. 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 self-signature of such a certificate is that disabled or unsupported message digests used for the signature are not treated as fatal errors.

When X509_V_FLAG_TRUSTED_FIRST is set, which is always the case since OpenSSL 1.1.0, construction of the certificate chain in X509_verify_cert(3) searches the trust store for issuer certificates before searching the provided untrusted certificates. Local issuer certificates are often more likely to satisfy local security requirements and lead to a locally trusted root. This is especially important when some certificates in the trust store have explicit trust settings (see "TRUST SETTINGS" in openssl-x509(1)).

The X509_V_FLAG_NO_ALT_CHAINS flag could have been used before OpenSSL 1.1.0 to suppress 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 non-self-signed certificates in the trust store to be treated as trust anchors, in the same way as self-signed root CA certificates. This makes it possible to trust self-issued certificates as well as certificates issued by an intermediate CA without having to trust their 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 contained in the trust store is added to the chain, whether that certificate is a self-signed "root" certificate or a not self-signed "intermediate" or self-issued 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 functions which work in specific structures such as X509_STORE_CTX_set_flags() which are likely to be deprecated in a future release.

# 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.

# EXAMPLES

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), X509_check_host(3), X509_check_email(3), X509_check_ip(3), openssl-x509(1)

# HISTORY

The X509_V_FLAG_NO_ALT_CHAINS flag was added in OpenSSL 1.1.0. The flag X509_V_FLAG_CB_ISSUER_CHECK was deprecated in OpenSSL 1.1.0 and has no effect.

The X509_VERIFY_PARAM_get_hostflags() function was added in OpenSSL 1.1.0i.

The X509_VERIFY_PARAM_get0_host(), X509_VERIFY_PARAM_get0_email(), and X509_VERIFY_PARAM_get1_ip_asc() functions were added in OpenSSL 3.0.

The function X509_VERIFY_PARAM_add0_policy() was historically documented as enabling policy checking however the implementation has never done this. The documentation was changed to align with the implementation.

The X509_VERIFY_PARAM_get_purpose() function was added in OpenSSL 3.5.

# COPYRIGHT

Copyright 2009-2025 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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.