Configuring SSL Security
This chapter describes how to configure SSL on the Cisco 4700 Series Application Control Engine (ACE) appliance. This chapter contains the following sections:
•Configuring SSL Termination
•Configuring the ACE for SSL Termination Using the Device Manager GUI
•Configuring the ACE for SSL Termination Using the CLI
After reading this chapter, you should have a basic understanding of how the ACE appliance provides SSL security for your network and how to configure SSL termination, in which the ACE operates as an SSL server.
SSL configuration in an ACE establishes and maintains a SSL session between the ACE and another device. It provides for secure data transactions between a client and a server. SSL provides authentication, encryption, and data integrity in a Public Key Infrastructure (PKI), a set of policies and procedures that establishes a secure information exchange between devices.
In SSL, data is encrypted using one or more symmetric keys that are known only by the two endpoints in the transaction. In a key exchange, one device generates the symmetric key and then encrypts it using an asymmetric encryption scheme before transmitting the key to the other device.
Asymmetric encryption requires each device to have a unique key pair consisting of a public key and a private key. A private key is an encryption/decryption key known only to the parties exchanging the messages. A public key is a value provided by some designated authority as an encryption key that, combined with a private key derived from the public key, can be used to effectively encrypt messages and digital signatures. The two keys are mathematically related; data that is encrypted using the public key can only be decrypted using the corresponding private key, and vice versa.
SSL facilitates client and server authentication through the use of digital certificates. Digital certificates are a form of digital identification to prove the identity of the server to the client, or optionally, the client to the server. A certificate ensures that the identification information is correct and the public key embedded in it actually belongs to the client or server.
A Certificate Authority (CA) issues digital certificates in the context of a PKI. CAs are trusted authorities that sign certificates to verify their authenticity. As the certificate issuer, the CA uses its private key to sign the certificate. Upon receiving a certificate, a client uses the issuer's public key to decrypt and verify the certificate signature to ensure that the certificate was actually issued and signed by an authorized entity.
If you do not have a certificate and the corresponding key pair, you can use the ACE to generate a key pair and a certificate signing request (CSR) to apply for a certificate from a CA. The CA signs the CSR and returns the authorized digital certificate to you. The ACE supports import, export, and other management functions to manage the various certificates and key pair files within each context.
The client and server use the SSL handshake protocol to establish an SSL session between the two devices. During the handshake, the client and server negotiate the SSL parameters that they will use during the secure session. During the SSL handshake, the ACE uses an SSL proxy service, which includes the configuration of SSL session parameters, an RSA key pair, and a matching certificate.
The ACE applies SSL session parameters to an SSL proxy service. Creating an SSL parameter map allows you to apply the same SSL session parameters to different proxy services. The SSL session parameters include timeouts, close protocol behavior, and SSL version—SSL 3 and/or Transport Layer Security (TLS) 1. For more information on these parameters, see the Cisco 4700 Series Application Control Engine Appliance SSL Configuration Guide.
You can configure the ACE to act as a client or a server during an SSL session by defining operational attributes such as SSL session parameters, SSL key pairs and certificates, and traffic characteristics. When the traffic characteristics match the settings specified in the operational attributes, the ACE executes the actions associated with the SSL proxy service. Figure 9-1 shows the three basic SSL configurations in which the ACE is used to encrypt and decrypt data between the client and the server: SSL termination, SSL initiation, and end-to-end SSL.
Figure 9-1 ACE SSL Configurations
In SSL termination, an ACE context is configured for a front-end application in which the ACE operates as an SSL server that communicates with a client. When you define the flow between an ACE and a client, the ACE operates as a virtual SSL server by adding security services between a web browser (the client) and the HTTP connection (the server).
All inbound SSL flows that come from a client terminate at the ACE. After the connection is terminated, the ACE decrypts the ciphertext (encrypted content) from the client and sends the data as clear text (unencrypted content) to an HTTP server. For information about configuring the ACE for SSL termination, see the "Configuring SSL Termination" section.
In SSL initiation, an ACE context is configured for a back-end application in which the ACE operates as a client that communicates with an SSL server. When you define the flow between an ACE and an SSL server, the ACE operates as a client and initiates the SSL session. SSL initiation enables the ACE to receive clear text from a client and then establish an SSL session with an SSL server, joining the client and SSL server connections.
The ACE encrypts the clear text that it receives from the client and sends the data as ciphertext to an SSL server. The SSL server can either be an ACE configured for SSL termination (a virtual SSL server) or a real SSL server (web server). On the outbound flow from the SSL server, the ACE decrypts the ciphertext from the server and sends clear text back to the client. For more information on configuring the ACE for SSL initiation, see the Cisco 4700 Series Application Control Engine Appliance SSL Configuration Guide.
In end-to-end SSL, an ACE context is configured for both SSL termination and SSL initiation. You configure the ACE for end-to-end SSL when you have an application that requires secure SSL channels between the client and the ACE, and between the ACE and the SSL server.
For example, a transaction between banks requires end-to-end SSL to protect all financial information exchanged. End-to-end SSL also allows the ACE to insert load-balancing and security information into the data. The ACE decrypts the ciphertext that it receives and inserts load-balancing and firewall information into the clear text. The ACE then re-encrypts the data and passes the ciphertext to its intended destination. For more information on configuring the ACE for end-to-end SSL initiation, see the Cisco 4700 Application Control Engine Series Appliance SSL Configuration Guide.
Configuring SSL Termination
SSL termination occurs when the ACE, acting as an SSL proxy server, terminates an SSL connection from a client and then establishes a TCP connection to an HTTP server. When the ACE terminates the SSL connection, it decrypts the ciphertext from the client and transmits the data as clear text to the HTTP server.
Figure 9-2 shows the following network connections in which the ACE terminates the SSL connection with the client:
•Client to ACE—An SSL connection exists between the client and the ACE acting as an SSL proxy server.
•ACE to Server—A TCP connection exists between the ACE and the HTTP server.
Figure 9-2 SSL Termination
Before configuring the ACE for an SSL operation, you must first configure it for server load balancing. To configure your ACE for server load balancing, see Chapter 6, "Configuring Server Load Balancing."
SSL termination is a Layer 3 and Layer 4 application because it is based on the destination IP address of the inbound traffic flow from the client. When configuring a policy map for SSL termination, you associate the following elements:
•The SSL proxy service, including SSL session parameters, certificate, and key pair.
•The virtual SSL server IP address that the destination IP address of the inbound traffic must match (a class map). When a match occurs, the ACE negotiates with the client to establish an SSL connection.
You can configure the ACE for SSL termination by following these steps:
Step 1 Import a key file with a key pair.
Step 2 Import a certificate that matches the imported key pair.
Step 3 Configure a parameter map.
Step 4 Configure an SSL proxy service using the key pair, certificate, and parameter map.
Step 5 Create a virtual server for SSL termination using the SSL proxy service.
Step 6 Deploy the configuration.
This chapter describes how to configure the ACE for SSL termination using either the Device Manager GUI or the CLI.
Configuring the ACE for SSL Termination Using the Device Manager GUI
You can configure the ACE for SSL termination using the Device Manager GUI by following these steps:
Step 1 Choose the user context VC_web, and then choose SSL > Setup Sequence. The Setup Sequence window appears.
Step 2 Click Import SSL Key Pair to import a key file. The Import SSL Key Pair pane appears at the bottom of the SSL Setup Sequence window (Figure 9-3)
Figure 9-3 SSL Setup Sequence Window—Import SSL Key Pair Pane
Step 3 Enter the following parameters. Leave the remaining parameters blank or with their default values.
•IP Address: 172.25.91.100 (in order for this to work, you should use an IP address where you can access the remote key file)
•Remote File Name: C:\marketing.pem
•Local File Name: C:\marketing.pem
•User Name: Admin
•Password: (password for your FTP server)
•Confirm: (retype the password for your FTP server)
Step 4 Click Import to import the key file.
Step 5 Choose Import Certificates in the SSL Setup Sequence window. The Import Certificates pane appears (Figure 9-4).
Figure 9-4 SSL Setup Sequence Window—Import Certificates Pane
Step 6 Enter the following parameters. Leave the remaining parameters blank or with their default values.
•IP Address: 172.25.91.100 (in order for this to work, you should use an IP address where you can access the certificate file)
•Remote File Name: C:\marketing_cert.pem
•Local File Name: C:\marketing_cert.pem
•User Name: Admin
•Password: (password for your FTP server)
•Confirm: (retype the password for your FTP server)
Step 7 Click OK to import the certificate file.
Step 8 Choose SSL > Parameter Maps. The Parameter Maps pane appears (Figure 9-5).
Figure 9-5 Parameter Maps Pane
Step 9 Click Add to create a parameter map. The Parameter Map window appears (Figure 9-6).
Figure 9-6 Parameter Map Window
Step 10 Enter PM_SSL_termination in the Name field. Leave the remaining parameters blank or with their default values.
Step 11 Click Deploy Now to deploy the parameter map on the ACE appliance. The Parameter Map Cipher pane appears.
Step 12 Select Add in the Parameter Map Cipher pane (Figure 9-6).
Step 13 Accept the defaults and click Deploy Now in the Parameter Map Cipher pane to add a cipher to the parameter map.
Step 14 Create an SSL proxy service by choosing SSL > Proxy Service. The Proxy Service pane appears (Figure 9-7).
Figure 9-7 Proxy Service Pane
Step 15 Click Add to create a proxy service. The Proxy Service window appears (Figure 9-8).
Figure 9-8 Proxy Service Window
Step 16 Enter the following parameters. Leave the remaining parameters blank or with their default values.
•Keys: (choose the key file that you imported earlier)
•Certificates: (choose the certificate that you imported earlier)
•Parameter Maps: PM_SSL_termination
Step 17 Click Deploy Now to deploy the proxy service on the ACE appliance.
Step 18 Configure a virtual server for SSL termination by choosing Load Balancing > Virtual Servers. The Virtual Servers pane appears.
Step 19 Click Add to create a virtual server. The Add Virtual Server window appears (Figure 9-9).
Figure 9-9 Add Virtual Server on Virtual Context Window
Step 20 Enter the following parameters. Leave the remaining parameters blank or with their default values.
•Virtual Server Name: VIP_SSL
•Virtual IP Address: 10.10.40.11
•Transport Protocol: TCP
•Application Protocol: HTTPS
•Proxy Service Name: PS_SSL_termination
•Primary Action: Load Balance
•Server Farm: SF_web
Step 21 Click Deploy Now to deploy the virtual SSL server on the ACE appliance.
Configuring the ACE for SSL Termination Using the CLI
You can configure the ACE for SSL termination using the CLI by following these steps:
Step 1 Verify that you are operating in the desired context, by checking the CLI prompt. If necessary, change to the correct context.
host1/Admin# changeto VC_web
Step 2 Import the key file marketing.pem from an FTP server.
host1/VC_web# crypto import ftp 172.25.91.100 Admin /marketing.pem
Hash mark printing on (1024 bytes/hash mark).
Successfully imported file from remote server.
Step 3 Copy the certificate information from the certificate you received from the CA, and paste it into a certificate file called marketing_cert.pem.
host1/VC_web# crypto import terminal marketing_cert.pem
Enter PEM formatted data ending with a blank line or "quit" on a line
Step 4 Enter quit to close the file.
Step 5 Verify that the certificate matches the key pair.
host1/VC_web# crypto verify marketing.pem marketing_cert.pem
keypair in marketing.pem matches certificate in marketing_cert.pem
Step 6 Start configuring SSL termination by entering configuration mode.
Step 7 Create an SSL proxy service.
host1/VC_web(config)# ssl-proxy service PS_SSL_termination
Step 8 Configure the SSL proxy service by defining the key pair and corresponding certificate.
host1/VC_web(config-ssl-proxy)# key marketing
host1/VC_web(config-ssl-proxy)# cert marketing_cert
Step 9 Create a Layer 3 and Layer 4 class map and configure it with the input traffic match criteria.
host1/VC_web(config)# class-map CM_SSL
host1/VC_web(config-cmap)# match virtual-address 10.10.40.11 tcp any
Step 10 Create a policy map and associate with it the class map CM_SSL.
host1/VC_web(config)# policy-map multi-match PM_SSL
host1/VC_web(config-pmap)# class CM_SSL
Step 11 Associate the SSL proxy service PS_SSL_termination with the policy map.
host1/VC_web(config-pmap-c)# ssl-proxy server PS_SSL_termination
Step 12 Apply the policy map to the input traffic of the VLAN 400 interface.
host1/VC_web(config)# interface vlan 400
host1/VC_web(config-if)# service-policy input PM_SSL
Step 13 Display the running configuration to verify that the information that you just added is configured properly.
host1/VC_web(config-if)# do show running-config
In this chapter, you have configured a virtual server for SSL termination. In the next chapter, you will configure server health monitoring.