X509_verify_cert, X509_STORE_CTX_verify - discover and verify X509 certificate chain
#include <openssl/x509_vfy.h> int X509_verify_cert(X509_STORE_CTX *ctx); int X509_STORE_CTX_verify(X509_STORE_CTX *ctx);
The X509_verify_cert() function attempts to discover and validate a certificate chain based on parameters in ctx. The verification context, of type X509_STORE_CTX, can be constructed using X509_STORE_CTX_new(3) and X509_STORE_CTX_init(3). It usually includes a target certificate to be verified, a set of certificates serving as trust anchors, a list of non-trusted certificates that may be helpful for chain construction, flags such as X509_V_FLAG_X509_STRICT, and various other optional components such as a callback function that allows customizing the verification outcome. A complete description of the certificate verification process is contained in the openssl-verification-options(1) manual page.
Applications rarely call this function directly but it is used by OpenSSL internally for certificate validation, in both the S/MIME and SSL/TLS code.
A negative return value from X509_verify_cert() can occur if it is invoked incorrectly, such as with no certificate set in ctx, or when it is called twice in succession without reinitialising ctx for the second call. A negative return value can also happen due to internal resource problems or because an internal inconsistency has been detected or if a retry operation is requested during internal lookups (which never happens with standard lookup methods). Applications must interpret any return value <= 0 as an error.
The X509_STORE_CTX_verify() behaves like X509_verify_cert() except that its target certificate is the first element of the list of untrusted certificates in ctx unless a target certificate is set explicitly.
Both functions return 1 if a complete chain can be built and validated, otherwise they return 0, and in exceptional circumstances (such as malloc failure and internal errors) they can also return a negative code.
If a complete chain can be built and validated both functions return 1. If the certificate must be rejected on the basis of the data available or any required certificate status data is not available they return 0. If no definite answer possible they usually return a negative code.
On error or failure additional error information can be obtained by examining ctx using, for example, X509_STORE_CTX_get_error(3). Even if verification indicated success, the stored error code may be different from X509_V_OK, likely because a verification callback function has waived the error.
X509_STORE_CTX_verify() was added in OpenSSL 3.0.
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