10.6. Performing X.509 Certificate Verification with CryptoAPI


You have an X.509 certificate, and you want to verify its validity using Microsoft’s CryptoAPI on Windows.


CryptoAPI represents an X.509 certificate using a CERT_CONTEXT object. Another object, referenced by a HCERTSTORE handle, must be created to hold the certificates that will be required for verification, as well as any certificate revocation lists (CRLs) that may be necessary. The actual certificate verification is performed by calling the CertGetIssuerCertificateFromStore( ) function for each certificate in the hierarchy. This function will verify the signature, certificate validity times, and revocation status of each certificate as it obtains the issuer for each call. The last certificate in the hierarchy will have no issuing certificate and should be self-signed.


Call the CertGetIssuerCertificateFromStore( ) function for each certificate in the hierarchy, beginning with the subject certificate at the end of the chain. Each time CertGetIssuerCertificateFromStore( ) is called, CryptoAPI will attempt to locate the issuer of the subject certificate passed into it. If the issuer certificate is found, the signature of the subject certificate will be verified with the public key of the issuer certificate. In addition, time validity checks will be performed on the subject certificate, and the subject certificate will be compared against the issuer’s CRL if it is present in the store.

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