X509_VERIFY_PARAM_set_flags¶

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_peername - 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_peername(const X509_VERIFY_PARAM *param);

DESCRIPTION¶

An X509_VERIFY_PARAM object collects the configuration consumed by a certificate verification operation: the verification flags, the purpose and trust selectors, the verification time, the maximum chain depth, the required security level, the acceptable certificate policies, and the reference identifiers against which the peer certificate's names are matched. X509_VERIFY_PARAM objects are typically attached to an X509_STORE or an SSL_CTX/SSL and reach X509_verify_cert(3) through the X509_STORE_CTX being verified; values propagate from one parameter set to another according to the rules in "INHERITANCE FLAGS".

These functions manipulate an X509_VERIFY_PARAM. The functions for configuring its reference identifiers (hostnames, email addresses, and IP addresses) are documented in X509_VERIFY_PARAM_set1_host(3).

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_clear_flags() clears the flags flags in param.

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_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 selector in param to trust, which must be one of the X509_TRUST_* identifiers defined in openssl/x509_vfy.h. This is a legacy mechanism that most applications should not use; see "BUGS". There is no public getter for the trust selector.

X509_VERIFY_PARAM_set_time() sets the verification time in param to t, which is then used as the reference time for certificate and CRL validity-period checks in place of the current time. Calling this function automatically sets the X509_V_FLAG_USE_CHECK_TIME flag (see "Validity period (time)"). If X509_VERIFY_PARAM_set_time() has not been called, validity checks are performed against the current time.

X509_VERIFY_PARAM_get_time() returns the verification time configured on param.

X509_VERIFY_PARAM_add0_policy() adds policy to the acceptable policy set. Policy checking itself must be enabled separately, either by setting X509_V_FLAG_POLICY_CHECK via X509_VERIFY_PARAM_set_flags() or by calling X509_VERIFY_PARAM_set1_policies().

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. If X509_VERIFY_PARAM_set_depth() is not called, the verification depth defaults to 100. 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.

The remaining accessor on this page reports a result populated during certificate verification rather than a configured parameter: 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 returned 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.

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(), and X509_VERIFY_PARAM_set1_policies() return 1 for success and 0 for failure.

X509_VERIFY_PARAM_get0_peername() returns a pointer to the name from the peer certificate that matched a configured reference identifier, or NULL if no match has been recorded.

X509_VERIFY_PARAM_get_flags() returns the current verification flags.

X509_VERIFY_PARAM_get_inh_flags() returns the current inheritance flags.

X509_VERIFY_PARAM_set_time(), X509_VERIFY_PARAM_set_depth(), and X509_VERIFY_PARAM_set_auth_level() do not return values.

X509_VERIFY_PARAM_get_time() returns the verification time previously configured on param via X509_VERIFY_PARAM_set_time().

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 consist of zero or more of the following values ORed together. Unless noted otherwise, each flag is off by default.

Revocation checking¶

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_OCSP_RESP_CHECK enables Online Certificate Status Protocol (OCSP) checking for the certificate chain leaf certificate. An error occurs if a suitable OCSP response cannot be found.

X509_V_FLAG_OCSP_RESP_CHECK_ALL expands OCSP checking to the entire certificate chain if X509_V_FLAG_OCSP_RESP_CHECK has also been enabled, and is otherwise ignored.

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

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

Certificate policy checking¶

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 RFC 5280. Policy checking is automatically enabled if any of these flags is set.

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

Chain construction¶

When X509_V_FLAG_TRUSTED_FIRST is set, which is the default 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 suppresses checking for alternative chains. By default, when the initial untrusted-first chain fails to reach a trust anchor, the build is retried with progressively shorter untrusted prefixes in an attempt to find an alternative.

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 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.

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 does not 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.

Validity period (time)¶

X509_V_FLAG_USE_CHECK_TIME indicates that the time stored on the parameters should be used for validity period checks in place of the current time. This flag is set automatically by X509_VERIFY_PARAM_set_time(); applications do not normally manipulate it directly.

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() has been used to specify a verification time, the check is performed against the specified time and this flag has no effect.

Extension processing and strictness¶

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 verification strictly apply X509 rules.

X509_V_FLAG_ALLOW_PROXY_CERTS enables proxy certificate verification. By default, proxy certificates are not accepted.

Suite B compliance¶

These flags enable enforcement of the NSA Suite B cryptographic profile, a now-legacy profile that restricts chain validation to a specific subset of elliptic-curve algorithms. Suite B has been superseded by NSA's Commercial National Security Algorithm (CNSA) Suite for new deployments.

X509_V_FLAG_SUITEB_128_LOS_ONLY restricts the chain to the Suite B 128-bit level of security: certificates must use the NIST P-256 curve with ECDSA and SHA-256.

X509_V_FLAG_SUITEB_192_LOS restricts the chain to the Suite B 192-bit level of security: certificates must use the NIST P-384 curve with ECDSA and SHA-384.

X509_V_FLAG_SUITEB_128_LOS is the bitwise OR of the two flags above and permits either level of security in the chain, with the constraint that once a P-384 certificate has appeared in the chain, P-256 certificates may not subsequently be used.

INHERITANCE FLAGS¶

These flags control how the values stored in one X509_VERIFY_PARAM are copied into another when verification parameters are "inherited", for example when an SSL object inherits its verification parameters from the SSL_CTX that created it. In the descriptions below, "from" refers to the source X509_VERIFY_PARAM from which values are copied, and "to" refers to the destination X509_VERIFY_PARAM into which they are copied.

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 values are copied across whether they are set or not. Flags are 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.

TLS clients are recommended to set up validation of server hostname(s) and/or IP address (directly using the functions described in X509_VERIFY_PARAM_set1_host(3), or more conveniently using SSL_set1_host(3) or SSL_add1_host(3)) and to use SSL_set_tlsext_host_name(3) for Server Name Indication (SNI), which may be crucial also for correct routing of the connection request.

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 CRL checking is enabled, 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.

The X509_TRUST_* selectors used by X509_VERIFY_PARAM_set_trust() are deceptively named: although each mirrors a PKIX extended key usage, the selector does not check that extKeyUsage. It matches only auxiliary trust information that is never carried in the certificate itself but must be attached to the in-memory X509 object by the application; absent that, the selector has no effect. Use X509_VERIFY_PARAM_set_purpose() to constrain a certificate by its extended key usage instead.

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¶

SSL_CTX_set_security_level(3), X509_verify_cert(3), X509_VERIFY_PARAM_set1_host(3), X509_VERIFY_PARAM_set_hostflags(3), X509_check_host(3), X509_check_email(3), X509_check_ip(3), SSL_set_tlsext_host_name(3), openssl-x509(1)

HISTORY¶

Until OpenSSL 1.1.0, by default (unless X509_V_FLAG_TRUSTED_FIRST was set), when building a certificate chain, if the first certificate chain found was not trusted, OpenSSL would 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. Since OpenSSL 1.1.0 version, the X509_V_FLAG_TRUSTED_FIRST is set by default.

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 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 2009-2026 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.