When using SSL to secure communications, the SSL authentication mechanism known as Server Authentication is used. This is the minimum amount of security provided by SSL and allows the client to validate that the Server is what it says it is.
To ensure that someone has not stolen the server's private and public keys and is pretending to be the server, the server sends additional information with the public key so the client can confirm the identity of the server. The complete package of information sent to the client is called a digital certificate which conforms to the X.509 standard.
This X.509 digital certificate includes, among other things, the Distinguished Name (DN) of the Server organization, the public key created by the server organization, the Distinguished Name of the organization issuing the certificate, and the issuer's signature. The organization issuing the certificate may be a well-known Certificate Authority (CA) or you may issue (create) your own certificate, called a self-signed certificate.
To create a signature, the certificate issuer first generates a message digest from the owner's DN, the owner's public key, and the issuer's DN. The message digest is the result of hashing this information down to a small size, such as 128, 160, 256, or some other number of bits. The message digest result is unique for that information and is based on the hashing algorithm that is used. The message digest is encrypted with the issuer's private key to create the issuer's signature.
When the client receives the server certificate, the client must have the public key of the certificate signer. The public key is used to decrypt the message digest. The server certificate also contains the hashing algorithm used to create the message digest. The client uses the same algorithm to create another message digest using the Distinguished Names and public key information in the received server certificate. If this new message digest exactly matches the decrypted message digest (issuer's signature) created by the certificate issuer, the client can be assured that the certificate has not been altered. This method of authentication is dependent on the security of the private key that is used by the certificate issuer.
To conduct commercial business on the Internet, you should obtain a server certificate signed by a well-known Certificate Authority. Server certificates issued by a well-known CA gives the client high assurance that the server is authentic. Most client key rings have been primed with several well-known CA's certificates. That enables the client to authenticate a Server certificate signed by a well-known CA without having to first obtain the issuer's certificate which includes the public key. For relatively small, private networks within your own enterprise you can create your own self-signed server certificate. The only difference between a CA issued certificate and a self-signed certificate is the issuer's Distinguished Name and who's private key was used to encrypt the message digest. The client needs to use the correct public key to decrypt the message digest. The CA certificate containing the CA's public key is probably already in the client's key ring and it can be used to decrypt the CA signature (message digest). The self-signed certificate containing the organization's public key needs to be added to the client's list of signer certificates so the client can decrypt the signature (message digest) created when the self-signed certificate was created. Some client products allow the client to add the server certificate to its list of signer certificates when the server certificate is received during SSL negotiation. If the client is confident the certificate really came from the correct server, this is an easy way to add the certificate rather than getting a copy and adding it manually.
For server authentication to work, the server must have a private key and associated server certificate in the server key database file. The gskkyman utility or RACF® Common Keyring support can be used to manage the keys and certificates needed for SSL support. If the gskkyman utility was used to create the key ring, a password stash file is also required.
SSL requires a server certificate as part of its server authentication process. The server certificate and the Certificate Authority certificates are stored in a key ring (also referred to as a key database). The server's key ring can be created using the gskkyman utility provided by the System Secure Socket Layer (System SSL) element of z/OS® or by using RACF's certificate management support. The key ring is associated with a server or client using server or client specific statements.