Manual:X509 verify cert(3)
X509_verify_cert - discover and verify X509 certificte chain
#include <openssl/x509.h> int X509_verify_cert(X509_STORE_CTX *ctx);
The X509_verify_cert() function attempts to discover and validate a certificate chain based on parameters in ctx. A complete description of the process is contained in the verify(1) manual page.
If a complete chain can be built and validated this function returns 1, otherwise it return zero, in exceptional circumstances it can also return a negative code.
If the function fails additional error information can be obtained by examining ctx using, for example X509_STORE_CTX_get_error().
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.
The negative return value from X509_verify_cert() can only occur if no certificate is set in ctx (due to a programming error) or if a retry operation is requested during internal lookups (which never happens with standard lookup methods). It is however recommended that application check for <= 0 return value on error.
This function uses the header x509.h as opposed to most chain verification functiosn which use x509_vfy.h.
X509_verify_cert() is available in all versions of SSLeay and OpenSSL.