TLSv1.3 Decryption

Decrypt TLSv1.3 traffic to protect against threats in encrypted traffic while benefiting from TLSv1.3 application security and performance improvements.
You can decrypt, gain full visibility into, and prevent known and unknown threats in TLSv1.3 traffic. TLSv1.3 is the latest version of the TLS protocol, which provides application security and performance improvements. Your existing Decryption policies work with TLSv1.3 when you configure the associated Decryption profile to use TLSv1.3 as the minimum protocol version or to use TLSv1.3 or Max as the maximum protocol version. The firewall supports TLSv1.3 decryption for Forward Proxy, Inbound Inspection, Decryption Broker, and Decryption Port Mirroring.
To use TLSv1.3, the client and server must be able to negotiate TLSv1.3 ciphers. For websites that don’t support TLSv1.3, the firewall selects an older version of the TLS protocol that the server supports.
The firewall supports the following decryption algorithms for TLSv1.3:
  • TLS13-AES-128-GCM-SHA256
  • TLS13-AES-256-GCM-SHA384
  • TLS13-CHACHA20-POLY1305-SHA256
If the Decryption profile you apply to decrypted traffic specifies the protocol’s
Max Version
as
Max
, then the profile supports TLSv1.3 and automatically uses TLSv1.3 with sites that support TLSv1.3. Otherwise, to support TLSv1.3, set the
Max Version
to
Max
. When you upgrade to PAN-OS 10.0, all Decryption profiles with the
Max Version
set to
Max
are reset to
TLSv1.2
to provide automatic support for mobile applications that use pinned certificates and prevent that traffic from dropping.
Not all applications support the TLSv1.3 protocol. Follow decryption best practices, set the
Min Version
of the TLS protocol to
TLSv1.2
, and leave the
Max Version
setting as
Max
. If business needs require allowing a weaker TLS protocol, create a separate SSL Decryption profile with a
Min Version
that allows the weaker protocol and attach it to a Decryption policy that defines the traffic you need to allow with the weaker TLS protocol.
If your Decryption policy supports mobile applications, many of which use pinned certificates, set the
Max Version
to
TLSv1.2
. Because TLSv1.3 encrypts certificate information that was not encrypted in previous TLS versions, the firewall can’t automatically add decryption exclusions based on certificate information, which affects some mobile applications. Therefore, if you enable TLSv1.3, the firewall may drop some mobile application traffic unless you create a No Decryption policy for that traffic. If you know the mobile applications you use for business, consider creating a separate Decryption policy and profile for those applications so that you can enable TLSv1.3 for all other traffic.
Do not attach a No Decryption profile to Decryption policies for TLSv1.3 traffic that you don’t decrypt. A change from previous TLS versions is that TLSv1.3 encrypts certificate information, so the firewall no longer has visibility into that data and therefore cannot block sessions with expired certificates or untrusted issuers, so the profile has no effect. (The firewall can perform certificate checks with TLSv1.2 and earlier because those protocols do not encrypt certificate information and you should apply a No Decryption profile to their traffic.) However, you should create a Decryption policy for TLSv1.3 traffic that you don’t decrypt because the firewall doesn’t log undecrypted traffic unless a Decryption policy controls that traffic.
When you allow unsupported modes in the SSL Protocol Settings Decryption Profile, the firewall automatically adds the traffic to the Local Decryption Exclusion Cache. The firewall still decrypts and inspects traffic that is downgraded from TLSv1.3 to TLSv1.2 and the
Reason
shown in the cache for adding the server to the cache is TLS13_UNSUPPORTED.
If you downgrade from PAN-OS 10.0 to a previous version, any Decryption profile that specifies TLSv1.3 as the
Min Version
or the
Max Version
changes to the highest supported version. For example, downgrading from PAN-OS 10.0 to PAN-OS 9.1 would replace TLSv1.3 with TLSv1.2. If a Panorama device on PAN-OS 10.0 pushes the configuration to devices that run older versions of PAN-OS, any Decryption profile that specified TLSv1.3 as the
Min Version
or the
Max Version
also changes to highest supported version.
For TLSv1.3 traffic, PAN-OS supports Hardware Security Modules (HSMs) only for SSL Forward Proxy. It does not support HSMs for SSL Inbound Inspection.
You can configure an SSL Decryption profile that sets TLSv1.3 as the minimum allowed protocol version to achieve the tightest security. However, some applications don’t support TLSv1.3 and may not work if TLSv1.3 is the minimum allowed protocol. Apply a profile that sets TLSv1.3 as the minimum version only to application traffic that only supports TLSv1.3.
  1. Create a new SSL Decryption profile or edit an existing profile (
    Objects
    Decryption
    Decryption Profile
    ).
    If the profile is new, specify a profile
    Name
    .
  2. Select
    SSL Protocol Settings
    .
  3. Change the
    Min Version
    to
    TLSv1.3
    .
    decryption-profile-tlsv13-as-min.png
    Using
    Max
    for the
    Max Version
    ensures that the traffic which the profile controls can use the strongest available protocol version.
    Min Version
    sets the weakest version of the protocol that the traffic can use. Setting the minimum version to
    TLSv1.3
    means that the traffic must use TLSv1.3 (or greater) and that weaker protocol versions are blocked. (The Decryption Policy rule defines the traffic the profile controls.)
    When you configure TLSv1.3 as the
    Min Version
    , you must use Perfect Forward Secrecy (PFS) and the weaker key exchange, encryption, and authentication algorithms are not available.
  4. Configure any other Decryption profile settings you need to set or change.
  5. Click
    OK
    to save the profile.
  6. Attach the profile to the appropriate Decryption Policy rule to apply it to the appropriate traffic.

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