Cisco Cisco Web Security Appliance S690 User Guide

Once the CSR has been generated, submit it to a certificate authority (CA). The CA will return the 
certificate in PEM format.

If you are acquiring a certificate for the first time, search the Internet for “certificate authority services 
SSL server certificates,” and choose the service that best meets the needs of your organization. Follow 
the service’s instructions for obtaining an SSL certificate.

You can also generate and sign your own certificate. Tools for doing this are included with OpenSSL, 
free software from 

http://www.openssl.org

.

In addition to root certificate authority (CA) certificate verification, AsyncOS supports the use of 
intermediate certificate verification. Intermediate certificates are certificates issued by a trusted root CA 
which are then used to create additional certificates. This creates a chained line of trust. For example, a 
certificate may be issued by example.com who, in turn, is granted the rights to issue certificates by a 
trusted root CA. The certificate issued by example.com must be validated against example.com’s private 
key as well as the trusted root CA’s private key.

Servers send a “certificate chain” in an SSL handshake in order for clients (for example, browsers and 
in this case the WSA, which is a HTTPS proxy) to authenticate the server. Normally, the server 
certificate is signed by an intermediate certificate which in turn is signed by a trusted root certificate, 
and during the handshake, the server certificate and the entire certificate chain are presented to the client. 
As the root certificate is typically present in the Trusted Certificate store of the WSA, verification of the 
certificate chain is successful.

However, sometimes when the end-point entity certificate is changed on the server, necessary updates 
for the new chain are not performed. As a result, going forward the server presents only the server 
certificate during the SSL handshake and the WSA proxy is unable to verify the certificate chain since 
the intermediate certificate is missing.

Previously, the solution was manual intervention by the WSA administrator, who would upload the 
necessary intermediate certificate to the Trusted Certificate store. Now you can use the CLI command 

advancedproxyconfig

 > 

HTTPS

 > 

Do you want to enable automatic discovery and download of 

missing Intermediate Certificates?

 to enable “intermediate certificate discovery,” a process the 

WSA uses in an attempt to eliminate the manual step in these situations. 

Intermediate certificate discovery uses a method called “AIA chasing”: when presented with an 
untrusted certificate, the WSA examines it for an extension named “Authority Information Access.” This 
extension includes an optional CA Issuers URI field, which can be queried for the Issuer Certificate used 
to sign the server certificate in question. If it is available, the WSA fetches the issuer’s certificate 
recursively until the root CA certificate is obtained, and then tries to verify the chain again.

Cisco periodically releases upgrades (new software versions) and updates (changes to current software 
versions) for AsyncOS for Web and its components.