The BIG-IP^® system supports a large set of cipher suites that you can choose from to build the cipher string used for security negotiation.

Supported cipher suites include various combinations of encryption algorithms and authentication mechanisms, including RSA (Rivest Shamir Adleman), DSA (Digital Signature Algorithm), and ECDSA (Elliptic Curve Digital signature Algorithm).

The system includes a default cipher string represented by the keyword DEFAULT, which contains a subset of the cipher suites that the BIG-IP system supports.

A cipher rule is an object that contains cipher-related information such as an encryption algorithm and a key exchange method. The BIG-IP system will use one or more cipher rules within a cipher group, to build the cipher string that the system will use to negotiate SSL security parameters with a client or server system.

You can use pre-defined cipher rules that the BIG-IP system provides, or you can create your own. In either case, after you decide which cipher rules you want to use, you then specify the cipher rules within a cipher group, which is the object that builds the actual cipher string that the system will use during SSL negotiation. Then you just need to specify the cipher group within a Client SSL or Server SSL profile, and assign the profile to a virtual server.

An example of a cipher rule might be one that specifies only ciphers that use a particular bulk encryption algorithm and a key exchange method.

A cipher group contains a list of cipher rules, and the instructions that the BIG-IP^® system needs for building the cipher string it will use for security negotiation. The instructions tell the system which cipher rules to include in the string, and how to apply them (allow, disallow, and so on, and in what order).

Custom cipher groups

This illustration shows an example of a custom cipher group. Using this cipher group, the BIG-IP system builds the final cipher string using a user-created custom cipher rule named /Common/my_ecdhe_rsa and the pre-built cipher rule /Common/f5-default.

Notice that the system will exclude from the string any cipher suites defined in the pre-built cipher rule /Common/f5-hw_keys.

Also notice that the cipher group displays a preview of the final cipher string after the instructions are applied.

For security and performance reasons, consider the following recommendations:

• Always append cipher suites to the DEFAULT cipher string.
• Include a cipher string that specifies the ECC key type, because its shorter length speeds up encryption and decryption while still offering virtually the same level of security.
• Disable ADH ciphers but also include the keyword HIGH. To do this, just include both !ADH and :HIGH in your cipher string.
• For AES, DES, and RC4 encryption types, make sure you specify the DHE key exchange method. DHE uses Forward Privacy, which creates a key that it throws away after each session so that the same session key never gets used twice. When you use DHE, make sure that the SSL private key isn't being shared with a monitoring system or a security device like an intrusion detection or prevention system. And by the way, diagnostic tools like ssldump won't work when you're using Forward Secrecy.
• Disable EXPORT ciphers by including !EXPORT in the cipher string.
• If you can live with removing support for the SSLv3 protocol version, do it. This protocol version is unsecure. Simply include :!SSLv3 in any cipher string you build.

1. Using a console access application such as PuTTY, log in to the advanced shell on the BIG-IP system.
2. At the system prompt, type either tmm --clientciphers all or tmm --serverciphers all.
   The system lists all supported cipher suites for either client-side or server-side traffic.

1. On the Main tab, click Local Traffic > Ciphers > Groups .
   The screen displays a list of pre-built cipher groups.
2. In the Name column, click the name of a cipher group.
   For example, click /Common/f5-ecc.
   The system displays the contents of the cipher group.
3. In the Available Cipher Rules list, find the corresponding cipher rule and click the plus sign to view the cipher suites included in the rule.

   For example, this shows the pre-built cipher group /Common/f5-ecc and the cipher suites included in it.

   
   If the cipher suites in the corresponding cipher rule are not sufficient for your cipher string, you'll need to create your own custom cipher group.
4. Click Cancel.
5. As an option, you can repeat this task for any other pre-built cipher groups.

1. On the Main tab, click Local Traffic > Ciphers > Rules .
   The screen displays a list of pre-built cipher rules.
2. Click Create.
3. In the Name field, type a name for the cipher rule.
   Note: Never include the prefix f5- in a cipher rule name. This prefix is reserved for pre-built cipher rules only.

   For example:

   
4. In the Cipher String field, type a cipher string that represents one or more cipher suites.

   For example:

   
5. Click Finished.

1. On the Main tab, click Local Traffic > Ciphers > Groups .
   The screen displays a list of pre-built cipher groups.
2. Click Create.
3. In the Name field, type a name for the cipher group.
   Note: Never include the prefix f5- in a cipher rule name. This prefix is reserved for pre-built cipher groups only.
4. If you created any custom rules, then in the Cipher Creation area of the screen in the Available Cipher Rules list, verify that the custom rules appear in the list.
5. For each cipher rule in the Available Cipher Rules list, click the plus sign to view the cipher suites included in the rule.

   For example, this shows the cipher suites included in the pre-built cipher rule named /Common/f5-ecc.

   
6. In the Available Cipher Rules list, select the boxes for the cipher rules you want to allow for negotiating security for SSL connections.
   Important: We strongly recommend that you select the cipher rule /Common/f5-default, and for added security, select other cipher rules, too.

   Here's an example of a list of available cipher rules that you might see within a cipher group. Notice that we've selected both a pre-built cipher rule and a custom cipher rule:

   
7. Move the selected cipher rules to the Allow the following box.

   Here we see that we're instructing the BIG-IP system to allow, during security negotiation, the cipher suites contained in the selected cipher rules:

   
8. Again from the Available Cipher Rules list, select the boxes for the cipher rules you want to restrict the allowed cipher rules to when negotiating security for SSL connections.
9. Using the Move button, move the selected cipher rules to the Restrict the Allowed list to the following box.
10. If you want to exclude any cipher rules from the allowed list, then from the Available Cipher Rules list, select the boxes for the rules you want to exclude.
11. Using the Move button, move the selected cipher rules to the Exclude the following from the Allowed list box.
12. From the Order list, select the order that you want the BIG-IP system to use when negotiating SSL connections.
    The choices are: Default, Speed, Strength, FIPS, and Hardware.
13. In the Cipher Audit area of the screen, view the cipher string that the BIG-IP system will construct based on the selections you made in the previous steps.
14. Click Finished.

1. On the Main tab, click Local Traffic > Profiles > SSL > Client or Local Traffic > Profiles > SSL > Server .
   The Client SSL or Server SSL profile list screen opens.
2. Click the name of a profile.
3. From the Configuration list, select Advanced.
4. On the right side of the screen, select the Custom check box.
5. For the Ciphers setting, click Cipher Group and from the list, select a custom cipher group.

   This shows a custom cipher group selected for the Ciphers setting:

   
6. Click Update.

1. On the Main tab, click Local Traffic > Virtual Servers .
   The Virtual Server List screen opens.
2. Click the name of a virtual server.
3. From the Configuration list, select Advanced.
4. For the SSL Profile (Client) and the SSL Profile (Server) settings, from the Available list, select the name of the SSL profile you previously created, and move the name to the Selected list:
   
   Using the SSL Profile (Server) setting is optional.
5. Click Update to save the changes.