Zilog EZ80F91AZA - Manual (Page 54)

UM020107-1211 SSL Configuration
ZTP Network Security SSL Plug-In
User Manual
48
Certificate Verification
Prior to using X.509 certificates, SSL clients and servers will perform integrity checks on
the certificate to determine if it is authentic. For ZTP Network Security SSL Plug-In serv-
ers, these checks occur during the SSL handshake protocol’s initialization call (see the
SSL Handshake Protocol Initialization section on page 22). For clients, these checks occur
when the server’s certificate chain is received during the establishment of a session.
In the ZTP Network Security SSL Plug-In implementation, the following items are veri-
fied for each certificate in the chain:
•
X.509 certificate structure
•
The certificate’s validity period is checked
•
Certificate Signature (can be disabled)
•
If the certificate is self-signed

By default, if the certificate contains all of the expected fields, is presented within its
validity period, its signature has been verified and the certificate is not self-signed, the
ZTP Network Security SSL Plug-In will implicitly trust the certificate. If any of these
checks fail, a user-modifiable callback function is called. This callback function is named
VerifyCertificate , and the default implementation (as shown in the following code
fragment) is present in the Certificate.c configuration file.
SSL_STATUS VerifyCertificate
(
SSL_X509_S * pCertificate
)
{
return( SSL_SUCCESS );
}
The purpose of this callback routine is to allow an application to examine information
regarding a suspect certificate. If the
VerifyCertificate callback returns
SSL_SUCCESS , the certificate will be trusted and used to complete the establishment of a
session. If the callback function returns SSL_FAILURE , the certificate will not be trusted;
this situation will prevent an SSL session from being established. The default implementa-
tion simply accepts all suspect certificates.
The flags member of the SSL_X509_S structure referenced by the pCertificate
pointer contains a combination of one or more of the following values which indicate the
results of processing the certificate:
#define SSL_X509_PARSED_OK 0x01
#define SSL_X509_DATE_VALID 0x02