SSL offload and acceleration

SSL profile infrastructure

Vulnerabilities in SSLv3 and RC4 implementation have emphasized the need to use the latest ciphers and protocols to negotiate the security settings for a network connection. Implementing any changes to the configuration, such as disabling SSLv3 across thousands of SSL end points, is a cumbersome process. Therefore, settings that were part of the SSL end points configuration have been moved to the SSL profiles, along with the default ciphers. To implement changes in the configuration, including cipher support, you need only modify the profile that is bound to the entities.

The default front-end and default back-end SSL profiles contain all the default ciphers and ECC curves, in addition to the settings that were part of the old profiles. Sample outputs for the default profiles are provided in the appendix. The Enable Default Profile operation automatically binds the default front-end profile to all front-end entities, and the default back-end profile to all back-end entities. You can modify a default profile to suit your deployment. You can also create custom profiles and bind them to SSL entities.

The front-end profile contains parameters applicable to a front-end entity. That is, they apply to the entity that receives requests from a client. Typically, this entity is an SSL virtual server or transparent SSL service on the Citrix ADC appliance. The back-end profile contains parameters applicable to a back-end entity. That is, they apply to the entity on the ADC appliance that sends client requests to a back-end server. Typically, this entity is an SSL service on the Citrix ADC appliance. If you try to configure an unsupported parameter, the error ERROR: Specified parameters are not applicable for this type of SSL profile appears.

Important:

  • An SSL profile takes precedence over SSL parameters. That is, if you configure SSL parameters using the set ssl parameter command, and later bind a profile to an SSL entity, the settings in the profile take precedence.

  • After the upgrade, if you enable the default profiles, you cannot undo the changes. That is, the profiles cannot be disabled. Save the configuration and create a copy of the configuration file (ns.conf) before enabling the profiles. However, if you do not want to use the features in the default profile, you can continue to use the old SSL profiles. For more information about these profiles, see Legacy SSL profile.

  • From release 11.1 51.x, in the GUI and CLI, a confirmation prompt is added when you enable the default profile to prevent enabling it by mistake.

Command:

set ssl parameter -defaultProfile ENABLED
    Save your configuration before enabling the Default profile. You cannot undo the changes. Are you sure you want to enable the Default profile? [Y/N]Y
Done

By default, some SSL parameters, called global parameters, apply to all the SSL end points. However, if a profile is bound to an SSL end point, the global parameters do not apply. The settings specified in the profile apply instead.

Points to note

  1. A profile can be bound to multiple virtual servers, but a virtual server can have only one profile bound to it.
  2. To delete a profile that is bound to a virtual server, first unbind the profile.
  3. A cipher or cipher group can be bound to multiple profiles at different priorities.
  4. A profile can have multiple ciphers and cipher groups bound at different priorities.
  5. Changes to a cipher group are immediately reflected in all the profiles and in all the virtual servers that one of the profiles is bound to.
  6. If a cipher suite is part of a cipher group, edit the cipher group to remove that cipher suite before removing the cipher suite from the profile.
  7. If you do not assign a priority to a cipher suite or cipher group attached to a profile, it is assigned the lowest priority within the profile.
  8. You can create a custom cipher group (also called a user-defined cipher group) from existing cipher groups and cipher suites. If you create cipher group A and add existing cipher groups X and Y to it, in that order, Y is assigned at a lower priority than X. That is, the group that is added first has a higher priority.
  9. If a cipher suite is part of two cipher groups attached to the same profile, the cipher suite is not added as part of the second cipher group. The cipher suite at the higher priority is in effect when traffic is processed.
  10. Cipher groups are not expanded in the profile. As a result, the number of lines in the configuration file (ns.conf) is greatly reduced. For example, if two cipher groups containing 15 ciphers each are bound to a thousand SSL virtual servers, expansion adds 30*1000 cipher-related entries in the configuration file. With the new profile, it would have only two entries: one for each cipher group that is bound to a profile.
  11. Creating a user defined cipher group from existing ciphers and cipher groups is a copy-paste operation. Any changes in the original group are not reflected in the new group.
  12. A user-defined cipher group lists all the profiles that it is a part of.
  13. A profile lists all the SSL virtual server, services, and service groups that it is bound to.
  14. If the default SSL profile feature is enabled, use the profile to set or change any of the attributes of an SSL entity. For example, virtual server, service, service group, or an internal service.

Save the configuration by using the CLI

At the command prompt, type:

save config

shell

root@ns# cd /nsconfig

root@ns# cp ns.conf ns.conf.NS<currentreleasenumber><currentbuildnumber>

Example:

save config
shell
root@ns# cd /nsconfig
root@ns# cp ns.conf ns.conf.NS.11.0.jun.16

Enable the default profile

Important:

Save your configuration before you upgrade the software and enable the default profiles.

From release 11.1 build 51.x, in the GUI and CLI, a confirmation prompt appears when you enable the default profile to avoid enabling it by mistake.

Command: The following command enables the default profile and binds this profile to the SSL entities to which a profile is already bound. That is, if a profile (for example P1) is already bound to an SSL entity, the default front-end profile or the default back-end profile replaces P1. The older profile (P1) is not deleted. It is now an enhanced SSL profile and contains the earlier settings, and the ciphers and ECC curves. If you do not want the default profile, you can explicitly bind P1 to the SSL entity.

set ssl parameter -defaultProfile ENABLED
    Save your configuration before enabling the Default profile. You cannot undo the changes. Are you sure you want to enable the Default profile? [Y/N]Y
Done

Upgrade the software to a build that supports the enhanced profile infrastructure, and then enable the default profiles.

Notes:

  • If a legacy profile (P1) is already bound to an SSL entity, and you enable the default profile, the default profile overrides the earlier binding. That is, the default profile is bound to the SSL entities. If you do not want the default profile to be bound, you must bind P1 to the SSL entity again.

  • A single operation (Enable Default Profile or set ssl parameter -defaultProfile ENABLED) enables (binds) both the default front-end profile and the default back-end profile.

Use case

After you enable the default profiles, they are bound to all the SSL end points. The default profiles are editable. If your deployment uses most of the default settings and changes only a few parameters, you can edit the default profiles. The changes are immediately reflected across all the end points. You can also create custom SSL profiles with some custom and some default parameters and bind it to the SSL entities.

The following flowchart explains the steps that you must perform:

SSL profiles use case 1

  1. For information about upgrading the software, see Upgrading the System Software.

  2. Enable the default profiles by using the CLI or GUI.

  • At the command line, type: set ssl parameter -defaultProfile ENABLED
  • If you prefer to use the GUI, navigate to Traffic Management > SSL > Change advanced SSL settings, scroll down, and select Enable Default Profile.

If a profile was not bound to an end point before the upgrade, a default profile is bound to the SSL end point. If a profile was bound to an end point before the upgrade, the same profile is bound after the upgrade, and default ciphers are added to the profile.

  1. (Optional) Manually change any settings in the default profile.
  • At the command line, type: set ssl profile <name> followed by the parameters to modify.
  • If you prefer to use the GUI, navigate to System > Profiles. In SSL Profiles, select a profile and click Edit.

SSL profile parameters

You can set the following SSL parameters in an SSL profile. You can set some of these parameters in an SSL virtual server. For more information about SSL virtual server parameters, see SSL virtual server parameters.

Support for secure renegotiation at the back end of a Citrix ADC appliance

Note: This parameter is introduced in release 13.0 build 58.x and later. In earlier releases and builds, only non-secure renegotiation was supported on the back end.

The feature is supported on the following platforms:

  • VPX
  • MPX platforms containing N2 or N3 chips
  • Intel Coleto SSL chip based platforms

The feature is not yet supported on the FIPS platform.

Secure renegotiation is denied by default on the back end of an ADC appliance. That is, the denySSLReneg parameter is set to ALL (default).

To allow secure renegotiation on the back end, select from one of the following settings for the denySSLReneg parameter:

  • NO
  • FRONTEND_CLIENT
  • FRONTEND_CLIENTSERVER
  • NONSECURE

Enable secure renegotiation by using the CLI

At the command prompt, type:

set ssl profile <name> -denySSLReneg <denySSLReneg>

Example:

set ssl profile ns_default_ssl_profile_backend -denySSLReneg NONSECURE
 Done

sh ssl profile ns_default_ssl_profile_backend
1)  Name: ns_default_ssl_profile_backend    (Back-End)
    SSLv3: DISABLED TLSv1.0: ENABLED  TLSv1.1: ENABLED  TLSv1.2: ENABLED  TLSv1.3: DISABLED
    Server Auth: DISABLED
    Use only bound CA certificates: DISABLED
    Strict CA checks:       NO
    Session Reuse: ENABLED      Timeout: 300 seconds
    DH: DISABLED
    Ephemeral RSA: DISABLED
    Deny SSL Renegotiation      NONSECURE
    Non FIPS Ciphers: DISABLED
    Cipher Redirect: DISABLED
    SSL Redirect: DISABLED
    Send Close-Notify: YES
    Strict Sig-Digest Check: DISABLED
    Push Encryption Trigger: Always
    PUSH encryption trigger timeout:    1 ms
    SNI: DISABLED
    OCSP Stapling: DISABLED
    Strict Host Header check for SNI enabled SSL sessions:      NO
    Push flag:  0x0 (Auto)
    SSL quantum size:       8 kB
    Encryption trigger timeout  100 mS
    Encryption trigger packet count:    45

    ECC Curve: P_256, P_384, P_224, P_521

1)  Cipher Name: DEFAULT_BACKEND        Priority :2
    Description: Predefined Cipher Alias

1)  Service Name: s187
 Done

Enable secure renegotiation by using the GUI

  1. Navigate to System > Profiles > SSL Profile.
  2. Add or edit a profile.
  3. Set Deny SSL Renegotiation to any value other than ALL.

    Back-end secure renegotiation SSL profile

Host header validation

Note: This parameter is introduced in release 13.0 build 52.x.

With HTTP/1.1, clients had to use multiple connections to process multiple requests. With HTTP/2, clients can reuse connections across domains that are covered by the same certificate. To accommodate this change, for an SNI enabled session, the ADC appliance must be able to control how the HTTP host header is validated. In earlier builds, the request was dropped if the parameter was enabled (set to “Yes”) and the request did not contain the host header for an SNI enabled session. If the parameter was disabled (set to “No”), the appliance did not perform the validation. A new parameter SNIHTTPHostMatch is added to an SSL profile and SSL global parameters to have better control on this validation. This parameter can take three values; CERT, STRICT, and NONE. These values work as follows for SNI enabled sessions only. SNI must be enabled on the SSL virtual server or the profile bound to the virtual server, and the HTTP request must contain the host header.

  • CERT - Connection is forwarded if the host header value in the request is covered by the certificate used to establish this SSL session.
  • STRICT - Connection is forwarded only if the host header value in the request matches the server name value passed in the Client Hello message of the SSL connection.
  • NO - The host header value is not validated.

Possible values: NO, CERT, STRICT Default value: CERT

With the introduction of the new parameter SNIHTTPHostMatch there is a change in the behavior of the dropReqWithNoHostHeader parameter. The setting of the dropReqWithNoHostHeader parameter no longer affects how the host header is validated against the SNI certificate.

Set SSL profile parameters by using the CLI

At the command prompt, type:

set ssl profile <name> [-ssllogProfile <string>] [-dh ( ENABLED | DISABLED ) -dhFile <string>] [-dhCount <positive_integer>][-dhKeyExpSizeLimit ( ENABLED | DISABLED )] [-eRSA ( ENABLED | DISABLED) [-eRSACount <positive_integer>]] [-sessReuse ( ENABLED | DISABLED )
[-sessTimeout <positive_integer>]] [-cipherRedirect ( ENABLED | DISABLED ) [-cipherURL <URL>]] [-clientAuth ( ENABLED | DISABLED )[-clientCert ( Mandatory | Optional )]] [-sslRedirect ( ENABLED |
DISABLED )] [-redirectPortRewrite ( ENABLED | DISABLED )] [-ssl3 (ENABLED | DISABLED )] [-tls1 ( ENABLED | DISABLED )] [-tls11 ( ENABLED| DISABLED )] [-tls12 ( ENABLED | DISABLED )] [-tls13 ( ENABLED |DISABLED )] [-SNIEnable ( ENABLED | DISABLED )] [-ocspStapling (ENABLED | DISABLED )] [-serverAuth ( ENABLED | DISABLED )] [-commonName <string>] [-pushEncTrigger <pushEncTrigger>] [-sendCloseNotify ( YES |
NO )] [-clearTextPort <port|*>] [-insertionEncoding ( Unicode | UTF-8)] [-denySSLReneg <denySSLReneg>] [-quantumSize <quantumSize>]
[-strictCAChecks ( YES | NO )] [-encryptTriggerPktCount <positive_integer>] [-pushFlag <positive_integer>][-dropReqWithNoHostHeader ( YES | NO )] [-SNIHTTPHostMatch <SNIHTTPHostMatch>] [-pushEncTriggerTimeout <positive_integer>]
[-sslTriggerTimeout <positive_integer>] [-clientAuthUseBoundCAChain (ENABLED | DISABLED )] [-sslInterception ( ENABLED | DISABLED )][-ssliReneg ( ENABLED | DISABLED )] [-ssliOCSPCheck ( ENABLED | DISABLED )] [-ssliMaxSessPerServer <positive_integer>] [-HSTS ( ENABLED| DISABLED )] [-maxage <positive_integer>] [-IncludeSubdomains ( YES | NO )] [-preload ( YES | NO )] [-sessionTicket ( ENABLED | DISABLED )][-sessionTicketLifeTime <positive_integer>] [-sessionTicketKeyRefresh (ENABLED | DISABLED )] {-sessionTicketKeyData } [-sessionKeyLifeTime <positive_integer>] [-prevSessionKeyLifeTime <positive_integer>]
[-cipherName <string> -cipherPriority <positive_integer>][-strictSigDigestCheck ( ENABLED | DISABLED )]
[-skipClientCertPolicyCheck ( ENABLED | DISABLED )] [-zeroRttEarlyData ( ENABLED | DISABLED )] [-tls13SessionTicketsPerAuthContext
<positive_integer>] [-dheKeyExchangeWithPsk ( YES | NO )]

Set SSL profile parameters by using the GUI

To add a profile:

  1. Navigate to System > Profiles. System profiles
  2. Select SSL Profiles. Click Add. SSL profile
  3. Specify values for the different parameters. SSL profile parameters
  4. Click OK.
  5. Click Done.

To reuse an existing SSL profile:

  1. Navigate to System > Profiles.
  2. Select an existing profile and click Add.
  3. Specify a different name, change any parameters, and click OK.
  4. Click Done.

TLS session ticket extension

An SSL handshake is a CPU-intensive operation. If session reuse is enabled, the server/client key exchange operation is skipped for existing clients. They are allowed to resume their sessions. This action improves the response time and increases the number of SSL transactions per second that a server can support. However, the server must store details of each session state, which consumes memory and is difficult to share among multiple servers if requests are load balanced across servers.

Citrix ADC appliances support the SessionTicket TLS extension. Use of this extension indicates that the session details are stored on the client instead of on the server. The client must indicate that it supports this mechanism by including the session ticket TLS extension in the client Hello message. For new clients, this extension is empty. The server sends a new session ticket in the NewSessionTicket handshake message. The session ticket is encrypted by using a key-pair known only to the server. If a server cannot issue a new ticket now, it completes a regular handshake.

This feature is available only in front-end SSL profiles, and only at the front end of communication in which the appliance acts as a server and generates session tickets.

Limitations

  • This feature is not supported on a FIPS platform.
  • This feature is supported only with TLS versions 1.1 and 1.2.
  • SSL session ID persistency is not supported with session tickets.

Enable TLS session ticket extension by using the CLI

At the command prompt, type:

set ssl profile <name> -sessionTicket (ENABLED | DISABLED ) [-sessionTicketLifeTime <positive_integer>

Arguments:

sessionTicket: State of TLS session ticket extension. Use of this extension indicates that the session details are stored on the client instead of on the server, as defined in RFC 5077.

Possible values: ENABLED, DISABLED

Default value: DISABLED

sessionTicketLifeTime: Specify a time, in seconds, after which the session ticket expires and a new SSL handshake must be initiated.

Default value: 300

Minimum value: 0

Maximum value: 172800

Example:

add ssl profile profile1 -sessionTicket ENABLED -sessionTicketlifeTime 300
Done

Enable TLS session ticket extension by using the GUI

  1. Navigate to System > Profiles. Select SSL Profiles.
  2. Click Add and specify a name for the profile.
  3. Select Session ticket.
  4. Optionally, specify Session Ticket Lifetime (secs).

Secure implementation of session tickets

By using TLS session tickets, clients can use abbreviated handshakes for faster reconnection to servers. However, if session tickets aren’t encrypted or changed for long periods of time, they can pose a security risk. You can secure session tickets by encrypting them with a symmetric key. To achieve forward secrecy, you can specify a time interval at which the session-ticket key is refreshed.

The appliance generates the session ticket keys by default. However, if multiple appliances in a deployment need to decrypt each other’s session tickets, they must all use the same session-ticket key. Therefore, you must set (add or load) the same session-ticket key data manually on all the appliances. Session-ticket key data includes the following information:

  • Session ticket name.
  • Session AES key used to encrypt or decrypt the ticket.
  • Session HMAC key used to compute the digest of the ticket.

You can now configure session ticket key data of length 64 bytes to support 256-bit HMAC keys as recommended in RFC 5077. Key lengths of 48 bytes are also supported for backward compatibility.

Note:

While typing the session-ticket key data manually, ensure that the configuration across all the Citrix ADC appliances in an HA setup or in a cluster setup is the same.

The sessionTicketKeyLifeTime parameter specifies how often a session-ticket key is refreshed. You can set the prevSessionTicketKeyLifeTime parameter to specify how long the previous session-ticket key will be maintained for decrypting tickets using that key, after a new key is generated. The prevSessionTicketKeyLifeTime setting extends the time for which a client can use an abbreviated handshake to reconnect. For example, if sessionTicketKeyLifeTime is set to 10 minutes and prevSessionTicketKeyLifeTime to 5 minutes, a new key is generated after 10 minutes and used for all new sessions. However, previously connected clients have another 5 minutes for which previously issued tickets are honored for an abbreviated handshake.

Configure SSL session-ticket data by using the CLI

At the command prompt, type:

set ssl profile <name> -sessionTicket ENABLED -sessionTicketLifeTime <positive_integer> -sessionTicketKeyRefresh ( ENABLED | DISABLED )] -sessionTicketKeyLifeTime <positive_integer> [-prevSessionTicketKeyLifeTime <positive_integer>]

Arguments:

sessionTicket: Use session tickets as described by RFC 5077. Establishing the initial handshake requires CPU-intensive public key encryption operations. With the ENABLED setting, a server issues a session ticket to a client, which the client can use to perform an abbreviated handshake.

Possible values: ENABLED, DISABLED. Default: DISABLED

sessionTicketLifeTime: Lifetime, in seconds, of the session ticket. After this time expires, clients cannot use this ticket to resume their sessions.

Maximum value: 172800. Minimum value: 0. Default: 300.

sessionTicketKeyRefresh: When the time specified by the session-ticket key lifetime parameter expires, regenerate the session-ticket key used to encrypt or decrypt the session tickets. Automatically enabled if sessionTicket is enabled. Disabled if an administrator enters the session-ticket data.

Possible values: ENABLED, DISABLED. Default: ENABLED

sessionKeyLifeTime: Lifetime, in seconds, of a symmetric key used to encrypt the session tickets issued by a Citrix ADC appliance.

Maximum value: 86400. Minimum value: 600. Default: 3000

prevSessionKeyLifeTime: Time, in seconds, for which the previous symmetric key used to encrypt session tickets remains valid for existing clients after the session-ticket key lifetime expires. Within this time, existing clients can resume their sessions by using the previous session ticket key. Session tickets for new clients are encrypted by using the new key.

Maximum value: 172800. Minimum value: 0. Default: 0

Example:

set ssl profile ns_default_ssl_profile_frontend -sessionTicket ENABLED -sessionTicketlifeTime 120 -sessionTicketKeyRefresh ENABLED -sessionTicketKeyLifeTime 100 -prevSessionTicketKeyLifeTime 60

Done

show ssl profile ns_default_ssl_profile_frontend

    Session Ticket: ENABLED
    Session Ticket Lifetime: 120 (secs)
    Session Key Auto Refresh: ENABLED
    Session Key Lifetime: 100 (secs)
    Previous Session Key Lifetime: 60 (secs)

Configure SSL session-ticket data by using the GUI

  1. Navigate to System > Profiles, and select SSL Profile.

  2. Select ns_default_ssl_profile_frontend and click Edit.

  3. In the Basic Settings section, click the pencil icon and set the following parameters:

    • Session Ticket
    • Session Ticket Lifetime (secs)
    • Session Ticket Key Auto Refresh
    • Session Ticket Key Lifetime (secs)
    • Previous Session Ticket Key Lifetime (secs)
  4. Click OK.

Type SSL session ticket data manually by using the CLI

At the command prompt, type:

set ssl profile <name> -sessionTicket ENABLED

set ssl profile <name> -sessionTicketKeyData

show ssl profile ns_default_ssl_profile_frontend

Arguments:

sessionTicket: Use of session tickets as described by RFC 5077. Establishing the initial handshake requires CPU-intensive public key encryption operations. With the ENABLED setting, a server issues a session ticket to a client, which the client can use to perform an abbreviated handshake.

Possible values: ENABLED, DISABLED. Default: DISABLED

sessionTicketKeyData: Contains the session ticket name (0–15 bytes), the session AES key used to encrypt or decrypt the session ticket (16–31 bytes), and the session HMAC key used to compute the digest of the ticket (32–63 bytes). Externally generated by an administrator and added to a Citrix ADC appliance.

Maximum length: 64 bytes

Example:

set ssl profile ns_default_ssl_profile_frontend -sessionTicket ENABLED

Done

set ssl profile ns_default_ssl_profile_frontend -sessionTicketKeyData 111111111111111111111111111111111111111111111111

Done

show ssl profile ns_default_ssl_profile_frontend

    1) Name: ns_default_ssl_profile_frontend (Front-End)
    SSLv3: ENABLED TLSv1.0: ENABLED TLSv1.1: ENABLED TLSv1.2: ENABLED
    Client Auth: DISABLED
    Use only bound CA certificates: DISABLED
    Strict CA checks: NO
    Session Reuse: ENABLED Timeout: 120 seconds
    DH: DISABLED
    DH Private-Key Exponent Size Limit: DISABLED Ephemeral RSA: ENABLED Refresh Count: 0
    Deny SSL Renegotiation ALL
    Non FIPS Ciphers: DISABLED
    Cipher Redirect: DISABLED
    SSL Redirect: DISABLED
    Send Close-Notify: YES
    Push Encryption Trigger: Always
    PUSH encryption trigger timeout: 1 ms
    SNI: DISABLED
    OCSP Stapling: DISABLED
    Strict Host Header check for SNI enabled SSL sessions: NO
    Push flag: 0x0 (Auto)
    SSL quantum size: 8 kB
    Encryption trigger timeout 100 mS
    Encryption trigger packet count: 45
    Subject/Issuer Name Insertion Format: Unicode
    Session Ticket: ENABLED
    Session Ticket Lifetime: 300 (secs)
    Session Key Auto Refresh: DISABLED
    Session Key Lifetime: 3000 (secs)
    Previous Session Key Lifetime: 0 (secs)
    Session Key Data: 84dad1afc6d56b0deeb0a7fd7f299a207e8d8c15cdd087a5684a11a329fd732e87a0535d90883
    47e8c181ba266f5c8838ae472cb3ab9255b683bf922fad32cee816c329989ef7cdeb278e93ac37882e3

    ECC Curve: P_256, P_384, P_224, P_521

    1) Cipher Name: DEFAULT Priority :4
    Description: Predefined Cipher Alias

    1) Internal Service Name (Front-End): nsrnatsip-127.0.0.1-5061
    2) Internal Service Name (Front-End): nskrpcs-127.0.0.1-3009
    3) Internal Service Name (Front-End): nshttps-::1l-443
    4) Internal Service Name (Front-End): nsrpcs-::1l-3008
    5) Internal Service Name (Front-End): nshttps-127.0.0.1-443
    6) Internal Service Name (Front-End): nsrpcs-127.0.0.1-3008
    7) Vserver Name: v1

Done

Type SSL session ticket data manually by using the GUI

  1. Navigate to System > Profiles, and select SSL Profile.

  2. Select ns_default_ssl_profile_frontend and click Edit.

  3. In the Basic Settings section, click the pencil icon and set the following parameters:

    • Session Ticket
    • Session Ticket Key Data
    • Confirm Session Ticket Key Data
  4. Click OK.

Support for Extended Master Secret in SSL handshake on Citrix ADC non-FIPS platforms

Note: This parameter is introduced in release 13.0 build 61.x.

Extended Master Secret (EMS) is an optional extension to the Transport Layer Security (TLS) protocol. To support EMS on the Citrix ADC appliance, a new parameter is added that applies to both front end and back end SSL profiles. If the parameter is enabled and the peer supports EMS, the ADC appliance uses the EMS calculation. If the peer does not support EMS, then the EMS calculation is not used for the connection even though the parameter is enabled on the appliance. For more information about EMS, see RFC 7627.

Note: Extended Master Secret is only applicable for handshakes that use TLS protocol version 1.0, 1.1, or 1.2.

Platform support for EMS

  • MPX and SDX platforms containing either Cavium N3 chips or Intel Coleto Creek crypto cards. The following platforms ship with Intel Coleto chips:
  • MPX 5900
  • MPX/SDX 8900
  • MPX/SDX 26000
  • MPX/SDX 26000-50S
  • MPS/SDX 26000-100G
  • MPX/SDX 15000-50G

You can also use the “show hardware’ command to identify whether your appliance has Coleto (COL) or N3 chips.

  • MPX and SDX platforms without crypto cards (software-only).

  • Software-only platforms: VPX, CPX, and BLX.

EMS cannot be enabled on the following platforms:

  • MPX 9700 FIPS and MPX 14000 FIPS platforms.

  • MPX and SDX platforms containing Cavium N2 crypto chips.

If the parameter is enabled, the ADC appliance attempts to use EMS in TLS 1.2, TLS 1.1, and TLS 1.0 connections. The setting does not affect TLS 1.3 or SSLv3 connections.

To allow EMS to be negotiated with the peer, enable the setting on the SSL profile bound to the virtual server (front end) or service (back end).

Enable extended master secret using the CLI

At the command prompt, type:

set ssl profile <profile name> [-allowExtendedMasterSecret (YES | NO)]

Examples

set ssl profile ns_default_ssl_profile_frontend  -allowExtendedMasterSecret YES

set ssl profile ns_default_ssl_profile_backend  -allowExtendedMasterSecret YES

The following table shows the default value of the allowExtendedMasterSecret parameter on different default and user defined profiles.

Profile Default setting
Default front-end profile NO
Default front-end secure profile YES
Default back-end profile NO
User-defined profile NO

Enable extended master secret using the GUI

  1. Navigate to System > Profiles > SSL Profile.
  2. Add a profile or edit a profile.
  3. Set Allow Extended Master Secret to YES.

    Extended master secret

Support for processing of ALPN extension in the client hello message

Note: This feature is supported in release 13.0 build 61.x and later.

To negotiate the application protocol in the ALPN extension for the connections handled by the SSL_TCP virtual server, a parameter alpnProtocol is added to the front-end SSL profiles. Only the protocol specified in the SSL profile is negotiated, if the same protocol is received in the ALPN extension of the client hello message.

Note: The alpnProtocol parameter is supported only on front end SSL profiles and is applicable to the SSL connections handled by SSL_TCP type virtual servers.

Set the protocol in the front-end SSL profile using the CLI

At the command prompt, type:

set ssl profile ns_default_ssl_profile_frontend -alpnProtocol <protocol_name>

The alpnProtocol parameter can take three values. Maximum length: 4096 bytes.

  • NONE: Application protocol negotiation does not take place. This setting is the default.
  • HTTP1: HTTP1 can be negotiated as the application protocol.
  • HTTP2: HTTP2 can be negotiated as the application protocol.

Example:

set ssl profile ns_default_ssl_profile_frontend -ALPNProtocol HTTP2
> sh ssl profile ns_default_ssl_profile_frontend
1)  Name: ns_default_ssl_profile_frontend   (Front-End)
    SSLv3: DISABLED TLSv1.0: ENABLED  TLSv1.1: ENABLED  TLSv1.2: ENABLED  TLSv1.3: DISABLED
    Client Auth: DISABLED
    Use only bound CA certificates: DISABLED
    Strict CA checks:   NO
    Session Reuse: ENABLED  Timeout: 120 seconds
    DH: DISABLED
    DH Private-Key Exponent Size Limit: DISABLED    Ephemeral RSA: ENABLED  Refresh Count: 0
    Deny SSL Renegotiation  ALL
    Non FIPS Ciphers: DISABLED
    Cipher Redirect: DISABLED
    SSL Redirect: DISABLED
    Send Close-Notify: YES
    Strict Sig-Digest Check: DISABLED
    Zero RTT Early Data: DISABLED
    DHE Key Exchange With PSK: NO
    Tickets Per Authentication Context: 1
    Push Encryption Trigger: Always
    PUSH encryption trigger timeout:    1 ms
    SNI: DISABLED
    OCSP Stapling: DISABLED
    Strict Host Header check for SNI enabled SSL sessions:  NO
    Match HTTP Host header with SNI:    CERT
    Push flag:  0x0 (Auto)
    SSL quantum size:   8 kB
    Encryption trigger timeout  100 mS
    Encryption trigger packet count:    45
    Subject/Issuer Name Insertion Format:   Unicode

    SSL Interception: DISABLED
    SSL Interception OCSP Check: ENABLED
    SSL Interception End to End Renegotiation: ENABLED
    SSL Interception Maximum Reuse Sessions per Server: 10
    Session Ticket: DISABLED
    HSTS: DISABLED
    HSTS IncludeSubDomains: NO
    HSTS Max-Age: 0
    HSTS Preload: NO
    Allow Extended Master Secret: NO
    Send ALPN Protocol: HTTP2

 Done

Set the protocol in the front-end SSL profile using the GUI

  1. Navigate to System > Profiles, and select SSL Profile.

  2. Select ns_default_ssl_profile_frontend and click Edit.

  3. In the ALPN Protocol list, select HTTP2.

    ALPN protocol selection in GUI

Load an old configuration

Enabling the default profiles is not reversible. However, if you decide that your deployment does not require the default profiles, you can load an older configuration that you saved before you enabled the default profiles. The changes are effective after you restart the appliance.

Load an old configuration by using the CLI

At the command prompt, type:

shell

root@ns# clear config

root@ns# cd /nsconfig

root@ns# cp ns.conf.NS.11.0.jun.16 ns.conf

root@ns# reboot