Chapter 22. Using Authentication Services

Secure RPC is a method of providing additional security that authenticates the host and the user making a request. Secure RPC uses Diffie-Hellman keypairs. This authentication mechanism uses DES (data encryption standard) public key encryption. Applications that use Secure RPC include NFS and the NIS+ name service.

NOTE

Starting with the Solaris 8 release, Kerberos V5 support is no longer provided as part of Secure RPC. However, a client-side implementation of Kerberos V5, which uses RPCSEC_GSS, is included with the Solaris 8 release.

The NFS software enables several hosts to share files over the network. The clients have access to the file systems that the server exports to the clients. Users logged in to the client system can access the file systems by mounting them from the server. To the user on the client system, the files seem to be local. One of the most common uses of the NFS environment is to enable systems, which act as NFS clients, to be installed for each user. However, each user's files are actually kept on a central NFS server. The file systems that contain these files are mounted to the clients as needed.

The NFS environment can use Secure RPC to authenticate users who make requests over the network. This combination is known as Secure NFS. The authentication mechanism, AUTH_DH, uses DES encryption with Diffie-Hellman authentication to ensure authorized access. The AUTH_DH mechanism has also been called AUTH_DES. As a whole, this method is called public key encryption, because it authenticates with the Diffie-Hellman keypairs, then encrypts everything after that with the DES algorithm.

Two kinds of encryption are in use today.

• Symmetric encryption.

• Asymmetric or public key encryption.

In symmetric encryption, a single secret key is shared by two parties (hence, the name symmetric). Any data encrypted with the secret key can be decrypted by anyone who has the secret key. Thus, it is important that only the parties involved possess the key. The algorithms that implement this type of encryption are very fast and efficient. However, the main problem with symmetric encryption is that the key must remain secret, which makes it difficult to transmit the key safely to the parties that need it. The key can be intercepted, thus defeating the encryption process.

In asymmetric encryption, each party generates a “keypair,” that consists of a public key and a private or secret key. The public key is made available to the universe, and the private key is available only to the party that created it. In fact, the private key is encrypted with a password so that it cannot be used directly if it is stolen. The a person's public key is used by other parties to encrypt information that can be decrypted only with the private key. For example, user A and user B generate keypairs for themselves and make their public keys available to each other. User A encrypts a message with user B's public key. This message can be decrypted only with user B's private key. In fact, even user A cannot decrypt this message because he didn't encrypt it with his own public key.

This process provides a safe method of encryption because each person exposes only his public key. The public keys can be used only to encrypt messages that are destined for themselves. Asymmetric encryption has another side benefit: only the owner of the private key can decrypt messages encrypted with his associated public key. Thus, by responding to an encrypted message, he can prove—or authenticate—his identity to the person that encrypted the message in the first place. The only problem with this form of encryption is that it is several orders of magnitude slower than symmetric encryption. Because of the slow speed, asymmetric encryption is useless for transmitting large amounts of data over a network.

So what do you do to transmit large amounts of information? You use both kinds of encryption.