Hi Mahesh,
There are two types of (CAs), root CAs and intermediate CAs. In order for a certificate to be trusted, and often for a secure connection to be established at all, that certificate must have been issued by a CA that is included in the trusted store of the device that is connecting.
If the certificate was not issued by a trusted CA, the connecting device (e.g., a web browser) will then check to see if the certificate of the issuing CA was issued by a trusted CA, and so on until either a trusted CA is found (at which point a trusted, secure connection will be established) or no trusted CA can be found (at which point the device will usually display an error).
To facilitate this process of verifying a «chain» of trust, every certificate includes the fields «Issued To» and «Issued By». An intermediate CA will show different information in these two fields, showing a connecting device where to continue checking, if necessary, in order to establish trust.
Root CA certificates, on the other hand, are «Issued To» and «Issued By» themselves, so no further checking is possible or necessary in order to establish trust (or lack thereof).
For example, if a certificate issued to «example.com» and issued by «Intermediate CA1», and the visiting web browser trusts «Root CA», trust may be established in the following manner:
- Certificate 1 - Issued To: example.com; Issued By: Intermediate CA 1
- Certificate 2 - Issued To: Intermediate CA 1; Issued By: Intermediate CA 2
- Certificate 3 - Issued To: Intermediate CA 2; Issued By: Intermediate CA 3
- Certificate 4 - Issued To: Intermediate CA 3; Issued By: Root CA
The visiting web browser trusts «Root CA», and a secure connection can now be established. Since this process is often called «certificate chaining», intermediate CA certificates are sometimes called «chained certificates». For enhanced security purposes, most end user certificates today are issued by intermediate certificate authorities.
Installing an intermediate CA signed certificate on a web server or load balancer usually requires installing a bundle of certificates.
Digital certificates provide digital identification for authentication. A digital certificate includes information that identifies a device or user, such as the name, serial number, company, department, or IP address. CAs are trusted authorities that “sign” certificates to verify their authenticity, thereby guaranteeing the identity of the device or user. CAs issue digital certificates in the context of a PKI, which uses public-key or private-key encryption to ensure security. For authentication using digital certificates, at least one identity certificate and its issuing CA certificate must exist on an ASA. This configuration allows multiple identities, roots, and certificate hierarchies.
http://www.cisco.com/c/en/us/td/docs/security/asa/asa84/asdm64/configuration_guide/asdm_64_config/access_certs.pdf
Regards,
Aditya
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Source--Wikipedia.
