The BIG-IP^® system uses Client Certificate Constrained Delegation (C3D) to support complete end-to-end encryption when interception of SSL traffic in a reverse proxy environment is required and when client certificates are used for mutual authentication.

When the BIG-IP receives a client certificate request from a backend server, the BIG-IP sends a forged copy of the client certificate. This maintains a full proxy approach and allows complete end-to-end encryption when intercepting SSL traffic in reverse proxy scenarios.

1. On the Main tab, click Local Traffic > Profiles > SSL > Client .
   The Client SSL profile list screen opens.
2. Click Create.
   The New Client SSL Profile screen opens.
3. In the Name field, type a unique name for the profile.
4. From the Parent Profile list, select clientssl.
5. Select the Custom check box.
   The settings become available for change.
6. From the Configuration list, select Advanced.
7. For the Mode setting, select the Enabled check box.
8. For the Certificate Key Chain setting, click Add.
   1. From the Certificate list, select a certificate name.
      This is the name of a certificate that you installed on the BIG-IP^® system. If you have not generated a certificate request nor installed a certificate on the BIG-IP system, and the BIG-IP system is not part of a device service clustering (DSC) configuration, you can specify the name of the existing certificate named default.

      Important: If the BIG-IP system is part of a DSC Sync-Failover group, always select a non-default certificate name, and ensure that this same certificate name is specified in every instance of this SSL profile in the device group. Taking these actions helps to ensure that SSL handshakes are successful after a failover event.
   2. From the Key list, select the name of the key associated with the certificate specified in the previous step.
      This is the name of a key that you installed on the BIG-IP^® system. If you have not installed a key on the BIG-IP system, and the BIG-IP system is not part of a device service clustering (DSC) configuration, you can specify the name of the existing key named default.

      Important: If the BIG-IP system is part of a DSC Sync-Failover group, always select a non-default key name, and ensure that this same key name is specified in every instance of this SSL profile in the device group. Taking these actions helps to ensure that SSL handshakes are successful after a failover event.
   3. From the Chain list, select the chain that you want to include in the certificate key chain.
      A certificate chain can contain either a series of public key certificates in Privacy Enhanced Mail (PEM) format or a series of one or more PEM files. A certificate chain can contain certificates for Intermediate certificate Authorities (CAs).

      Note: The default self-signed certificate and the default CA bundle certificate are not appropriate for use as a certificate chain.
   4. For the Passphrase field, type a string that enables access to SSL certificate/key pairs that are stored on the BIG-IP system with password protection.
      This setting is optional. For added security, the BIG-IP system automatically encrypts the pass phrase itself. This pass phrase encryption process is invisible to BIG-IP^® system administrative users.
   5. Click Add.
9. In the Certificate Key Chain setting, click Add again, and repeat the process for all certificate key chains that you want to specify.
   At a minimum, you must specify an RSA certificate key chain.
   The result is that all specified key chains appear in the text box.
10. To enable OCSP stapling, select theOCSP Stapling check box.
    To enable OCSP stapling, you must first create an OCSP Stapling profile. See Creating an OCSP stapling profile for detailed steps.
11. If you want to Notify Certificate Status to Virtual Server, select the check box.
12. For the Ciphers setting, specify a cipher group or cipher string by choosing one of these options.
    Note: If you specified an ECDSA certificate key chain in the Certificate Key Chain setting, you must include the cipher string ECDHE_ECDSA in the cipher group or cipher string that you specify in the Ciphers setting. (At a minimum, you should specify a cipher group or string such as DEFAULT:ECDHE_ECDSA.) This is necessary to ensure successful cipher negotiation when the BIG-IP system is offered an ECDSA-based certificate only.

    Option	Description
    Cipher Group	Select an existing cipher group from the list when you want to use a system-defined or custom cipher group to define the ciphers that the BIG-IP system uses for negotiating SSL connections. Here's an example of the Ciphers setting where we've selected a custom cipher group that we created earlier.
    Cipher String	Type a cipher string in the box if you want to manually specify a cipher string instead of selecting a cipher group. For security and performance reasons, consider following these recommendations: Always append ciphers to the DEFAULT cipher string. Type a cipher string that includes 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. Also, 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 not secure. Simply include :!SSLv3 in any cipher string you type. Here's an example of the Ciphers setting where we have opted to manually type the cipher string DEFAULT:ECDHE-RSA-AES-128-GCM-SHA256:!ADH:!EXPORT:HIGH:

13. For the Client Authentication area, select the Custom check box.
14. For Client Certificate list, specify whether you want to ignore, require, or request the client certificate authentication.
15. If you are enabling C3D, from the Trusted Certificate Authorities list, you must select a trusted CA bundle.
16. Select the Custom check box for the Client Certificate Constrained Delegation area.
    The settings become available for change.

    Note: See About client certificate constrained delegation prior to enabling C3D.
17. For the Client Certificate Constrained Delegation setting, select Enabled.
18. From the OCSP list, select the object that the BIG-IP system's SSL should use to connect to the OCSP responder and check the client certificate status.
    You can click the + icon to open the create-new OCSP object screen. See Creating an OCSP stapling profile for detailed steps.
19. For the Unknown OCSP Response Control list, specify the action the system takes when the OCSP object returns an unknown status:
    • If you want the connection to be dropped, retain the default value Drop.
    • If you want the connection to ignore the unknown status and continue, Select Ignore.
20. Click Finished.

1. On the Main tab, click Local Traffic > Profiles > SSL > Server .
   The Server SSL profile list screen opens.
2. Click Create.
   The New Server SSL Profile screen opens.
3. In the Name field, type a unique name for the profile.
4. From the Parent Profile list, select serverssl.
5. From the Configuration list, select Advanced.
6. Select the Custom check box.
   The settings become available for change.
7. From the Certificate list, select the name of an SSL certificate on the BIG-IP system.
   Important: If the BIG-IP system is part of a DSC Sync-Failover group, always select a non-default certificate name, and ensure that this same certificate name is specified in every instance of this SSL profile in the device group. Taking these actions helps to ensure that SSL handshakes are successful after a failover event.
8. From the Key list, select the name of an SSL key on the BIG-IP system.
   Important: If the BIG-IP system is part of a DSC Sync-Failover group, always select a non-default key name, and ensure that this same key name is specified in every instance of this SSL profile in the device group. Taking these actions helps to ensure that SSL handshakes are successful after a failover event.
9. In the Pass Phrase field, type a pass phrase that enables access to the certificate/key pair on the BIG-IP system.
10. From the Chain list, select the name of an SSL chain on the BIG-IP system.
11. For the Ciphers setting, specify a cipher group or cipher string by choosing one of these options.
    Note: If you specified an ECDSA certificate key chain in the Certificate Key Chain setting, you must include the cipher string ECDHE_ECDSA in the cipher group or cipher string that you specify in the Ciphers setting. (At a minimum, you should specify a cipher group or string such as DEFAULT:ECDHE_ECDSA.) This is necessary to ensure successful cipher negotiation when the BIG-IP system is offered an ECDSA-based certificate only.

    Option	Description
    Cipher Group	Select an existing cipher group from the list when you want to use a system-defined or custom cipher group to define the ciphers that the BIG-IP system uses for negotiating SSL connections. Here's an example of the Ciphers setting where we've selected a custom cipher group that we created earlier.
    Cipher String	Type a cipher string in the box if you want to manually specify a cipher string instead of selecting a cipher group. For security and performance reasons, consider following these recommendations: Always append ciphers to the DEFAULT cipher string. Type a cipher string that includes 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. Also, 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 not secure. Simply include :!SSLv3 in any cipher string you type. Here's an example of the Ciphers setting where we have opted to manually type the cipher string DEFAULT:ECDHE-RSA-AES-128-GCM-SHA256:!ADH:!EXPORT:HIGH:

12. Select the Custom check box for Server Authentication.
    The settings become available for change.
13. From the Frequency list, select either once or always.
14. From the OCSP list, select the OCSP object that the BIG-IP system's SSL should use to connect to the OCSP responder and to check the server certificate status. You can click the + icon to open the create-new OCSP object screen.
    The OCSP stapling object can be added in both forward and reverse proxy configurations. When the server SSL Forward Proxy property is set to Enabled, the forward proxy OCSP object is used to validate and staple the web server's certificate status. When the server SSL Forward Proxy property is set to Disabled, the reverse proxy OCSP object is used to reset the client connection if the web server certificate has been revoked.
15. Modify the other settings in this area of the screen as required.
16. Select the Custom check box for the Client Certificate Constrained Delegation section.
    The settings become available for change.

    Note: See About client certificate constrained delegation prior to enabling C3D.
17. From the Client Certificate Constrained Delegation setting, select Advanced.
18. From the Client Certificate Constrained Delegation list, select Enabled.
19. From the CA Certificate list, select the name of the certificate file that is used as the certification authority certificate.
20. From the CA Key list, select the name of the key file that is used as the certification authority key.
21. In the CA Passphrase field, type the passphrase of the key file that is used as the certification authority key.
    Note: This should be the passphrase corresponding to the specified CA Key.
22. For the Confirm CA Passphrase field, type the identical passphrase.
23. For the Certificate Lifespan fields, type the lifespan of the certificate generated that is using the SSL client certificate constrained delegation.
    The default is 1 day, 0 hours.
24. To define the extensions of the client certificates to be included in the generated certificates, from the Certificate Extensions list, select Extensions List.
25. For the Certificate Extensions List setting, click Disable or Enable to add or remove available extensions.
    • Basic Constraints: Uses basic constraints to indicate whether the certificate belongs to a CA.
    • Extended Key Usage: Uses Extended Key Usage, typically on a leaf certificate, to indicate the purpose of the public key contained in the certificate.
    • Key Usage: Provides a bitmap specifying the cryptographic operations that may be performed using the public key contained in the certificate; for example, it could indicate that the key should be used for signature but not for enciphering.
    • Subject Alternative Name: Allows identities to be bound to the subject of the certificate. These identities may be included in addition to, or in place of, the identity in the subject field of the certificate.

    You can also add extensions in the Custom extension field. Type in the extension name and click Add.

26. Click Finished.

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) setting, from the Available list, select the name of the Client SSL profile you previously created and move the name to the Selected list.
5. For the SSL Profile (Server) setting, from the Available list, select the name of the Server SSL profile you previously created and move the name to the Selected list.
6. Click Update to save the changes.

1. On the Main tab, click System > Certificate Management > Traffic Certificate Management > OCSP .
2. Click Create.
   The new OCSP Stapling Profile screen opens.
3. In the Name field, type a unique name for the OCSP stapling profile.
4. For the Use Proxy Server setting, specify how to fetch the OCSP response:
   • If you want the BIG-IP system to use the Proxy Server Pool, select the check box. Use this when there are one or more servers that can act as a proxy an HTTP request to an external server and fetch the response.
   • If you want to use the DNS Resolver, clear the check box. Use this when the OCSP responder can be reached on one of the BIG-IP system interfaces.
5. In the Proxy Server Pool or DNS Resolver field, select the proxy server pool or DNS resolver used for fetching the OCSP response.
6. In the Route Domain field, select the route domain for fetching an OCSP response using HTTP forward proxy.
7. In the Concurrent Connections Limit field, type the maximum number of connections per second allowed for the OCSP certificate validator.
   The default value is 50 connections.
8. In the Responder URL field, type the name of a URL that will override the OCSP responder URL obtained from the certificate's AIA extension.
   This must be an HTTP or HTTPS-based URL.
9. In the Timeout field, type a time interval for the BIG-IP system to wait before dropping the connection to the OCSP responder.
10. From the Trusted Responders list, select the name of a certificate to use to verify the response from the OCSP responder.
11. In the Clock Skew field, type a value for the maximum tolerable absolute difference between the clocks of the responder and the BIG-IP system.
12. In the Status Age field, type a value for the maximum allowed lag time in the OCSP response that the BIG-IP system accepts.
    If you type 0, the validation is skipped. The default value is 86400.
13. To have the system check the responder's certificate for the OCSP signing extension for the Options setting, select the Strict Responder Certificate Checking check box.
14. From the Timeout list, select a value that specifies the lifetime of the OCSP response.
    The default is Indefinite, indicating that the response validity period takes precedence.
15. In the Error Timeout field, type a value for how long a BIG-IP system will cache an error response.
    The default value is 3600 seconds.
    Note: The Error Timeout must be greater than Connection Timeout.
16. From the Certificate list, select a certificate corresponding to the key used for signing the OCSP request.
17. From the Key list, select a key to use to sign an OCSP request.
18. In the Passphrase field, type the passphrase of the key used to sign an OCSP request.
19. From the Hash Algorithm list, select the hash algorithm used to sign an OCSP request.
    The default is SHA256.
    Note: This is not the algorithm used in the certificate itself. It is what the OCSP responder will use when validating the request.
20. Click Finished.

1. On the Main tab, click System > Certificate Management > Traffic Certificate Management > OCSP > Statistics .
   The System OCSP statistics screen opens.
2. From the Statistics Type list, verify that OCSP is selected.
3. From the Data Format list, select how the system presents the statistics information.

   Option	Description
   Normalized (default)	Rounds values to the nearest whole number.
   Unformatted	Presents the actual value, including all decimal places.

4. From the Auto Refresh list, select a time interval to automatically update the statistics display screen information.
   The default is Disabled.
   When you specify an automatic-refresh interval, the system presents a Stop button for halting the operation, and counts down the seconds to the next update.

   Note: Short automatic-refresh intervals may negatively affect system performance.

This list defines terms for cipher-related features that the BIG-IP ^® system supports.

Some of the cipher suites that the BIG-IP system supports are included in a default cipher string that you can specify using the keyword DEFAULT. The keyword DEFAULT represents a set of ciphers that are suitable for most SSL connections.

The DEFAULT keyword appears as the default value in the Ciphers setting of the Client SSL and Server SSL profiles.

BIG-IP^® system version 14.0 does not support the OpenSSL cipher stack. As a result, the keyword NATIVE represents the only TLS stack in use and is equivalent to the keyword ALL.

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.

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.

For security and performance reasons, consider the following recommendations:

• Always append cipher suites to the default cipher string, respresented by the keyword DEFAULT.
• Don't use any of the keywords COMPAT, SSLv2, and RC2 in a cipher string. These keywords are invalid and resolve to a value of None.
• Instead of using the keyword NATIVE, use ALL. These keywords are equivalent, so use of NATIVE is unecessary.
• 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 Secrecy, 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. 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.

The BIG-IP system supports Elliptic Curve Cryptography (ECC). Because Elliptic Curve key sizes are significantly smaller than those of other key types, ECC is ideally suited for smaller, mobile devices for which key storage is an issue. On the BIG-IP system, ECC works with the SSL offload feature.

The BIG-IP^® system supports the Diffie-Hellman Ephemeral key exchange method, as well as other Diffie-Hellman variations. A Diffie–Hellman key exchange method is an alternative to RSA key exchange and allows the client and the BIG-IP system to establish a shared secret session key to use for communication.

You can cause Local Traffic Manager™ to handle authentication of clients or servers in certain ways. For client-side processing, the possible behaviors are:

Ignore

Ignore a certificate (or lack of one) and therefore never authenticate the client. The Ignore option is the default, and when used, causes any per-session authentication setting to be ignored.

Require

Require a client to present a valid and trusted certificate before granting access.

Request

Request and verify a client certificate. In this case, the SSL profile always grants access regardless of the status or absence of the certificate.

For server-side processing, the possible behaviors are:

Require

Require a server to present a valid and trusted certificate before granting access.

Ignore

Ignore a certificate (or lack of one) and therefore never authenticate the server. The Ignore value is the default setting, and when used, causes any per-session authentication setting to be ignored.

You can configure an SSL profile to require authentication either once per SSL session (once), or once upon each subsequent re-use of an SSL session (always). The default setting for this option is once.

Whether you set this value to once or always depends on your application. A well-designed web application should need to verify a certificate only once per session. F5 recommends for performance reasons that you use the default setting (once) whenever possible.

You can modify the SSL profile to require authentication not only once per session, but also upon each subsequent re-use of an SSL session.

You can use the Certificate Chain Traversal Depth setting of an SSL profile to configure the maximum number of CA certificates (intermediate CA certificates and/or root CA certificates) that can be traversed in the certificate chain. The default value is 9. If a longer chain is provided, and the client has not been authenticated within this number of traversals, client or server certificate verification fails.

Any certificates installed as part of a CA certificate bundle are trusted. All certificates sent by the peer are not trusted, and the BIG-IP system rejects v1/v2 intermediate certificates presented by the peer. The process of certificate chain building starts from a leaf certificate and ends when the issuer CA certificate is trusted.

For client-side and server-side SSL processing, you can use the Trusted Certificate Authorities setting on an SSL profile to configure an SSL profile to verify certificates presented by a client or a server. You can specify a client trusted CAs file name, which the BIG-IP^® system then uses to verify client or server certificates. If you do not configure a trusted CAs file, the system uses a default file.

The trusted CAs file that you specify for certificate verification contains one or more certificates, in Privacy Enhanced Mail (PEM) format. Built manually, this file contains a list of the client or server certificates that the SSL profile will trust. If you do not specify a trusted CAs file, or the specified trusted CAs file is not accessible to the BIG-IP system, the system uses the default file name.

For client-side profiles only, if you intend to configure the SSL profile to require or request client certificates for authentication, you will want the profile to send to clients a list of CAs that the BIG-IP^® system is likely to trust.

This list, known as the Client Certificate CA file, is different from the client Trusted CAs file. This is because, in some cases, you might have a client that does not possess a valid client certificate, in which case you might not want to reveal the actual list of CAs that the BIG-IP system trusts. The client certificate CA file solves this problem by allowing the BIG-IP system to advertise a list of CAs that is different from the actual client trusted CAs file configured as part of certificate verification.

Although the contents of the Client Certificate CA file can differ from that of the Client Trusted CAs file, it is best, for compatibility reasons, to set the Advertised Certificate Authorities setting to match the Trusted Certificate Authorities setting. This is because modern browsers might not permit SSL session negotiation to proceed if the peer that requests the client certificate does not provide a list of trusted CAs.

For server-side profiles only, Local Traffic Manager™ supports name-based authentication, which guards against man-in-the-middle attacks. When you configure the Authenticate Name setting for a server-side profile, Local Traffic Manager checks the name against the Common Name (CN) listed in the certificate that the target server presents to the BIG-IP^® system. If the name attribute that you specify does not match the CN in the server certificate, Local Traffic Manager closes the connection. An example of a CN is www.f5.com.

The Certificate Revocation List (CRL) setting of an SSL profile allows Local Traffic Manager™ to use CRLs to check revocation status of a certificate prior to authenticating a client or server.

As an alternative to using CRLs, you can use the Online Certificate Status Protocol (OCSP) feature, which ensures up-to-date information on certificate revocation status.