Manual Chapter : About BIG-IP cipher support

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Manual Chapter

About BIG-IP cipher support

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

The full set of cipher suites that the BIG-IP system supports are contained in the NATIVE cipher string. The cipher suites contained in both the DEFAULT and NATIVE cipher string are eligible for hardware acceleration.

The BIG-IP system supports a large set of cryptographic parameters that you can use to modify how the BIG-IP manages SSL/TLS connections.

For TLS 1.2 and TLS 1.3, you can configure all or some of the cryptographic parameters:

  • Ciphersuites.
  • Key exchange algorithms, for example RSA, DH, or ECDHE.
  • Signature algorithms, for example RSA or ECDSA.
  • Encryption primitives, for example AES128 or CAMELLIA.
  • Hash algorithms, for example SHA256.
  • Message authentication codes, for example HMAC-SHA256 or HMAC-SHA384.

Glossary of cipher-related terms

The BIG-IP system supports many cryptographic parameters used to negotiate SSL/TLS connections. The following list will help you understand how these parameters are organized on the BIG-IP system.

Cipher Group
A BIG-IP configuration object that specifies a list of cipher rules. The BIG-IP system offers several pre-built cipher groups, such as f5-default, f5-ecc, and f5-secure. You can use a pre-built cipher group or create a new custom cipher group. Cipher Groups can be associated with a Client or Server SSL profile's Cipher option to specify the allowed cryptographic parameters.
Cipher rule
A BIG-IP configuration object that specifies a list of cipher suites used to negotiate SSL/TLS connections. The BIG-IP system offers several pre-built cipher rules, such as f5-default, f5-ecc, and f5-secure. You can use a pre-built cipher rule or create a custom cipher rule. Cipher Rules are applied to Cipher Groups.
Cipher string
A BIG-IP named object that specifies a list of one or more cipher suites, for example DEFAULT or NATIVE. You can combine cipher strings to create the final cipher string that the BIG-IP system uses to negotiate SSL security parameters with another system. Cipher Strings can be associated with a Client or Server profile's Cipher option to specify the allowed cryptographic parameters.
Cipher Suites
A cipher suite is a combination of a key exchange method, authentication method, bulk encryption algorithm, and a message authentication code (MAC). The BIG-IP system uses cipher suites to negotiate the security parameters used to create SSL/TLS connections.
Rule Audit
The Rule Audit can be used when creating a custom Cipher Rule to display list of cipher suites contained in the cipher rule.
Group Audit
The Group Audit can be used when creating a custom Cipher Group, to display the list of cipher suites that will make up the final Cipher Group.

What is a cipher group?

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, restrict, or exclude, and in what order).

Pre-built cipher groups

The BIG-IP system offers a few pre-built cipher groups that you can choose from to use as is to build your final cipher string, However, it's common to create your own custom cipher group instead.

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.
Note: To create a custom SM2 cipher group to use when creating a custom client SSL profile that supports SM2, see the Create a custom Client SSL profile that supports SM2 section for task details. This section also provides information on creating a custom SM2 cipher rule.

About pre-built cipher groups

The BIG-IP system offers a set of pre-built cipher groups, with names containing the prefix f5-. Note that in general, a cipher group contains the cipher suites that you want to allow, restrict, or exclude when the system builds the cipher string used for SSL negotiation.

A pre-built cipher group allows all cipher suites specified in a corresponding pre-built cipher rule to be included in the final cipher string that the BIG-IP system builds for SSL negotiation. A prebuilt cipher group does not restrict the allowed cipher suites in any way, nor does it exclude any cipher suites.

This table lists and describes the pre-built cipher groups on the system.

Table 1. Descriptions of the pre-built cipher groups
Cipher group name Description
f5-aes Allows all cipher suites specified in the pre-built cipher rule f5-aes.
f5-default Allows all cipher suites specified in the pre-built cipher rule f5-default.
f5-ecc Allows all cipher suites specified in the pre-built cipher rule f5-ecc.
f5-hw_keys Allows all cipher suites specified in the pre-built cipher rule f5-hw_keys.
f5-secure Allows all cipher suites specified in the pre-built cipher rule f5-secure.

About 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.

Building a custom Cipher Group

Before starting this task, make sure you've confirmed the need to create a custom cipher string instead of using a pre-built cipher group.

You build a final, custom cipher string by creating a cipher group. A cipher group contains the cipher rules and instructions that the BIG-IP system needs for building the cipher string it will use for security negotiation with a client or server system.

Note: To create a custom SM2 cipher group to use when creating a custom client SSL profile that supports SM2, see the Create a custom Client SSL profile that supports SM2 section for task details. This section also provides information on creating a custom SM2 cipher rule.
  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. In the Group Details setting, 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. 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. 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 Cryptographic Parameters box, view the cipher suites that the BIG-IP system will use to construct the final cipher string, based on the selections you made in the previous steps.
  14. Click Finished.
After you complete this task, the BIG-IP system has a custom cipher group that the BIG-IP system will use to build the final cipher string.

What is a cipher rule?

A cipher rule is an object that contains a list of cipher suites. After you create a cipher rule, you specify it within a cipher group. A cipher group is the object that builds the actual cipher string that the system will use during SSL negotiation.

You can use pre-defined cipher rules that the BIG-IP system provides, or you can create your own.

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

Note: DH Groups and Signature Algorithms allow modification of TLS 1.2 and 1.3 key agreements and signature algorithms respectively.
Note: To create a custom SM2 cipher rule to use when creating a custom client SSL profile that supports SM2, see the Create a custom Client SSL profile that supports SM2 section for task details.

About pre-built cipher rules

Pre-built cipher rules

The BIG-IP system offers a set of pre-built cipher rules, with names containing the prefix f5-. This table lists these cipher rules and the cipher strings they represent.

Table 2. Pre-built cipher rules and their contents
Cipher rule name Associated cipher string
f5-aes AES
f5-default DEFAULT
f5-ecc ECDHE:ECDHE_ECDSA
f5-hw_keys ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES256-CBC-SHA:DHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES256-SHA256:DHE-RSA-AES256-SHA:ECDH-RSA-AES256-GCM-SHA384:ECDH-RSA-AES256-SHA384:ECDH
f5-secure ECDHE:RSA:!SSLV3:!RC4:!EXP:!DES

About custom cipher rules

You can use the following cryptographic parameters to create custom cipher rules:

Cipher suites
These represent the bulk encryption and hash algorithms used to negotiate SSL/TLS connections. An example of a cipher suite is ECDHE-RSA-AES128-CBC-SHA.
DH groups
In TLS 1.2 and 1.3, these are the Elliptic Curve Diffie Hellman (ECDH) key agreement algorithms used to negotiate SSL/TLS connections. The available key agreement curves are: P256, P384, and X25519.
Signature algorithms
In TLS 1.2 and 1.3, these are the digital signature algorithms for authentication. Examples of signature algorithms are rsa_pkcs1_sha256 and ecdsa_secp256r1_sha256.

Create a custom cipher rule

When you create your own cipher rules for inclusion in a custom cipher group, the BIG-IP system builds a cipher string that includes or excludes the cipher suites and algorithms needed for negotiating SSL connections.

Note: To create a custom SM2 cipher rule to use when creating a custom client SSL profile that supports SM2, see the Create a custom Client SSL profile that supports SM2 section for task details.
  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 Suites field, type one or more cipher suites.

    For example:

  5. In the DH Groups field, type one or more Elliptic Curve Diffie-Hellman key exchange algorithms, separated by commas (:).
    Note: The available named groups (formerly known as curves) are: secp256r1, secp384r1, and X25519. You can also type a special keyword, DEFAULT, which represents the recommended set of named groups.
    For example, you can specify secp256r1:X25519.
  6. In the Signature Algorithms field, type one or more signature algorithms, separated by commas (:), that you want to include in the cipher rule. You can also type a special keyword, DEFAULT, which represents the recommended set of signature algorithms.
    Note: The available signature algorithms are: DSA-SHA1, DSA-SHA256, DSA-SHA384, DSA-SHA512, ECDSA-SHA1, ECDSA-SHA256, ECDSA-SHA384, ECDSA-SHA512, RSA-PKCS1-SHA1, RSA-PKCS1-SHA256, RSA-PKCS1-SHA384, RCS-PKCS1-SHA512, RSA-PSS-SHA256, RSA-PSS-SHA384, and RSA-PSS-SHA512 .
    For example, you can specify RSA_PKCS1_SHA256:ECDSA_P256_SHA256.
  7. Click Finished.
The cipher rule now appears within any custom cipher group, in the list of available cipher rules.

About the DEFAULT and NATIVE cipher strings

The DEFAULT cipher string appears as the default value in the Ciphers setting of the Client SSL and Server SSL profiles and represents a subset of the cipher suites found in the NATIVE cipher suite.

The NATIVE cipher string represents the full set of BIG-IP supported cipher suites.

Both the DEFAULT and NATIVE cipher strings represent cipher suites that are eligible for hardware acceleration.

Important: We strongly recommend that you use the default cipher string and, for added security, append other cipher suites to it.

Viewing cipher suites in the DEFAULT and NATIVE cipher strings

Before you use this command, confirm that your BIG-IP user account grants you access to the advanced shell.

Follow these steps to display the cipher suites associated with the DEFAULT cipher string. This list of cipher suites is also included in the pre-built cipher rule f5-default.

  1. Using an SSH client application such as PuTTY, access the advanced shell on the BIG-IP system.
  2. At the system prompt, to view the DEFAULT cipher suites used for client-side negotiation, type the command tmm --clientciphers DEFAULT.
  3. At the system prompt, to view the DEFAULT cipher suites used for server-side negotiation, type the command tmm --serverciphers DEFAULT.

Best practices for BIG-IP cipher strings

For security and performance reasons, consider the following recommendations:

  • When modifying cipher suites, F5 strongly recommends that you append cipher suite modifications to the DEFAULT cipher string.
  • Include a cipher string that specifies the ECC key type. Due to their smaller size, ECC keys reduce computing costs while maintaining a similar 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 perfect forward secracy, which creates an ephemeral private key for each new secure connection. This ensures the same private key is never 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.

About Diffie-Hellman Ephemeral key exchange

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.

About DHE key exchange

Because Diffie-Hellman key exchange methods do not include authentication, use of Diffie-Hellman Ephemeral (DHE) requires that it be paired with an authentication mechanism. The DHE key exchange/authentication pairs that the BIG-IP system supports are:

  • DHE-RSA-* (Diffie-Hellman Ephemeral-RSA)
  • DHE-DSS-* (Diffie-Hellman Ephemeral-DSS)
  • ECDHE-RSA-* (Elliptic Curve Diffie-Hellman Ephemeral-RSA)
  • ECDHE-ECDSA-* (Elliptic Curve Diffie-Hellman Ephemeral-DSA)
Note: DHE key exchange methods, when paired with RSA and DSS authentication, are not included in the cipher rule f5-default nor in the cipher keyword DEFAULT.

About Perfect-Forward-Privacy

The Diffie-Hellman Ephemeral (DHE) key exchange method provides Perfect Forward Privacy (PFP). With standard Diffie-Hellman, multiple key exchanges all use the same session key, which can compromise security. By contrast, DHE uses PFP, which generates a disposable key per session and thereby ensures that the same session key is never used twice. No key remains to be disclosed, and if the private key of the server is discovered, past communication remains secure.

Supported Diffie-Hellman variations

The BIG-IP system supports all three Diffie-Hellman key exchange methods. They are:

Diffie-Hellman Ephemeral (DHE)
Diffie-Hellman Ephemeral uses temporary public keys. The authenticity of a temporary key can be verified by checking the digital signature included in the key exchange messages. The key exchange messages are signed using either the RSA or DSA algorithms, depending on the cipher being used. For example, DHE-RSA uses RSA to sign the key exchange messages. DHE includes Perfect Forward Secrecy (PFS), which means that a compromise of the system's long-term signing key does not affect the privacy of past sessions. Like FIPS, DHE prevents private key disclosure.
Diffie-Hellman (DH)
Diffie-Hellman embeds the system's public parameter in the certificate, and the CA then signs the certificate. That is, the certificate contains the Diffie-Hellman public-key parameters, and those parameters never change.
Anonymous Diffie-Hellman (ADH)
Anonymous Diffie-Hellman uses DH, but without authentication. The keys used in the exchange are not authenticated, resulting in keys being susceptible to security attacks.

Viewing a list of supported DHE ciphers

Before using this command, confirm that your user account grants you access to the advanced shell.
You perform this task when you want to display a specific set of ciphers that the BIG-IP system supports.
  1. Access the advanced shell on the BIG-IP system.
  2. At the system prompt, type the command tmm --clientciphers ciphers .
    For example, to see a list of DHE+DES ciphers, type tmm --clientciphers DHE:DHE_DSS. To see a list of ECDHE ciphers, type tmm --clientciphers ECDHE:ECDHE_ECDSA.

Specifying a Diffie-Hellman key exchange method

Use this task to modify an existing Client SSL profile to enable support for Diffie-Hellman key exchange.
  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. In the Name column, click the name of the profile you want to modify.
  3. Select the Custom check box.
    The settings become available for change.
  4. To specify DHE ciphers:
    1. From the Configuration list, select Advanced.
    2. For the Ciphers setting, click Cipher String and type DHE:DHE_DSS.
  5. Click Update.
After you perform this task and assign the profile to a virtual server, the BIG-IP uses the DHE key exchange method to establish secure communication with the relevant client or server.

Viewing DHE key exchange statistics

You can use the Traffic Management Shell (tmsh) to view statistics about the use of Diffie-Hellman ciphers in SSL negotiation.
  1. Access the system prompt on the BIG-IP system.
  2. From the BIG-IP system prompt, type tmsh show ltm profile client-ssl profile_name .
    An example of a name for a profile that specifies DHE ciphers is my_dhe_profile.
After you type this command, the BIG-IP system displays output such as the following. In this example, the profile statistics show that Diffie-Hellman Ephemeral (DHE) with RSA certificates has been used once:
Sample profile statistics for key exchange method

Sample profile statistics for key exchange method

About Elliptic Curve encryption

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.

About Elliptic Curve cipher support

The BIG-IP system supports multiple ciphers that use Elliptic Curve Cryptography (ECC) encryption with Diffie-Hellman key exchange. On the BIG-IP system, EC is used with DHE to establish the shared secret; however, the subsequent bulk encryption of data cannot be done with any ECC-based algorithm and must be done using conventional crypto algorithms such as AES and 3DES. For example, a typical Elliptic Curve cipher is: ECDHE-RSA-AES128-CBC-SHA.

The specific ECC ciphers that the BIG-IP system supports are:

  • ECDHE-RSA-*
  • ECDHE-ECDSA-*
  • ECDH-ECDSA-*

Because ECC with Diffie-Hellman does not include a mechanism for digitally signing handshake messages, the RSA or DSA algorithms are used to digitally sign the handshake messages to thwart Man-in-the-Middle attacks. For example, an ECDHE-ECDSA-* cipher suite uses the ECC DSA certificate specified in the Client SSL profile to digitally sign the handshake messages.

Note: Elliptic Curve ciphers with DSA are not included in the DEFAULT cipher suite.

Viewing ECDH key exchange statistics

You can use the Traffic Management Shell (tmsh) to view statistics about the use of Elliptic Curve Diffie-Hellman ciphers in SSL negotiation.
  1. Access the system prompt on the BIG-IP system.
  2. From the BIG-IP system prompt, type tmsh show ltm profile client-ssl profile_name | grep ECDH.
    An example of a name for a profile that specifies DHE ciphers is my_ecdh_profile.
After you type this command, the BIG-IP system displays output such as the following. In this example, the profile statistics show that ECDH with RSA certificates has been used six times:
Sample profile statistics for key exchange method

Sample profile statistics for key exchange method

Specifying an Elliptic Curve Diffie-Hellman key exchange method

Use this task to modify an existing Client SSL profile to enable support for Elliptic Curve Diffie-Hellman Ephemeral (ECDHE) key exchange.
  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. In the Name column, click the name of the profile you want to modify.
  3. Select the Custom check box.
    The settings become available for change.
  4. For the Ciphers setting, click Cipher String and type DEFAULT:ECDHE.
  5. Click Update.
After you perform this task and assign the profile to a virtual server, the BIG-IP system uses the ECDHE key exchange method to establish secure communication with the relevant client or server.

Unsupported cipher suites on the BIG-IP system

For security reasons, these cipher suites are unavailable in the BIG-IP system:

  • EXP-EDH-RSA-DES-CBC-SHA
  • EXP-ADH-DES-CBC-SHA
  • EXP-RC2-CBC-MD5
  • EXP-ADH-RC4-MD5

About cipher keywords on the BIG-IP system

There are a few things you should know when specifying keywords to create a BIG-IP cipher string. These things apply whether or not you are creating a cipher string using cipher rules and groups or typing a raw cipher string into an SSL profile.

About the COMPAT cipher string

In previous BIG-IP releases, cipher support included the COMPAT cipher string, allowing the use of OpenSSL cipher suites not natively supported by the BIG-IP. In this release, the COMPAT cipher string has been removed.

If your configuration includes the COMPAT cipher string, it will be replaced with NONE and secure connections relying on these cipher suites will fail.

This change:

  • Optimizes the security of your cipher configuration by preventing any OpenSSL cipher suite vulnerabilities from being introduced into the BIG-IP system.
  • Changes the meaning of the NATIVE keyword; this keyword now equivalent to the keyword ALL.

Invalid keywords for BIG-IP cipher strings

When you manually configure a cipher string on the BIG-IP system (as opposed to using a cipher group), these keywords are invalid:

  • COMPAT
  • SSLV2 (a subset of COMPAT)
  • RC2 (a subset of COMPAT)
  • Any other subsets of COMPAT or SSLv2

If you attempt to specify these keywords within a cipher string, the system displays an error message and prevents you from creating the relevant SSL profile.

Important: If you have an SSL profile in a previous BIG-IP version and then upgrade to version 14.0 or higher, the system automatically resolves the issue for you.

Changes to BIG-IP cipher keywords during a system upgrade

During a BIG-IP software upgrade to version 14.0 or higher, the system takes these actions:

  • If the system detects the keywords COMPAT, SSLv2, RC2, or any subset of these in an existing cipher string, the system logs a message in the file /var/log/ltm and changes any of these keywords to None.
  • The system treats the keyword NATIVE as being equivalent to keyword ALL.
  • If a cipher string evaluates to an empty set, the system remaps the string to the default cipher string, represented by the keyword DEFAULT. The default cipher string contains a subset of the cipher suites that are suitable for most SSL connections.