A signed certificate also contains details about the Certification Authority (CA). The CA digitally signs a certificate by adding its own organization details, an encrypted digest of the certificate, and its own public key. With this information encoded, the complete signed certificate can be verified as being correct.
There are dozens, perhaps hundreds, of CAs. A browser-or the user confronted by a browser warning-can't be expected to recognize the digital signatures from all these authorities. The X.509 certificate standard solves this problem by allowing issuing CAs to have their signatures digitally signed by a more authoritative CA, who can in turn have its signature signed by yet another, more trusted CA. Eventually the chain of signatures ends with that of a root Certification Authority. It is the certificates from the root CAs that are often preinstalled in a browser. Some browsers allow users to add their own trusted certificates.
Self-signed certificates can be created and used to configure a web server with SSL. We show how to create self-signed certificates in Appendix A. But will they be trusted? The answer is probably not for secure applications.updated