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Develop a Decryption Strategy
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Develop a Decryption Strategy

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Develop a Decryption Strategy

To understand the traffic you should and shouldn't decrypt, work with invested groups, including finance, HR, legal, and IT to ensure that you don’t decrypt sensitive traffic.
Where Can I Use This?What Do I Need?
No separate license required for decryption when using NGFWs or Prisma Access.
Note: The features and capabilities available to you in Strata Cloud Manager depend on your active license(s).
Work with stakeholders such as legal, finance, HR, executives, security, and IT or support personnel to develop a decryption deployment strategy. Start by getting the required approvals to decrypt traffic to secure the corporation. Decrypting traffic involves understanding how legal regulations and business needs affect what you can and can’t decrypt.
Identify and prioritize the traffic you want to decrypt. Best practice is to decrypt as much traffic as you can to gain visibility into potential threats in encrypted traffic and prevent those threats. If incorrect NGFW sizing prevents you from decrypting all the traffic you want to decrypt, prioritize the most critical servers, the highest-risk traffic categories, and less trusted segments and IP subnets. To help prioritize, ask yourself questions such as, “What happens if this server is compromised?” and “How much risk am I willing to take in relation to the level of performance I want to achieve?”
Identify traffic that you can’t decrypt because the traffic breaks decryption for technical reasons such as a pinned certificate, an incomplete certificate chain, unsupported ciphers, or mutual authentication. Decrypting sites that break decryption technically results in blocking that traffic. Evaluate websites that break decryption technically and ask yourself if access to those sites is needed for business reasons. If you don’t need access to those sites, allow decryption to block them. If access to any of those sites is needed for business purposes, add them to the SSL Decryption Exclusion list. The SSL Decryption Exclusion list is exclusively for sites that break decryption technically.
Identify sensitive traffic that you choose not to decrypt for legal, regulatory, personal, or other reasons, such as financial, health, or government traffic, or the traffic of certain executives. This is not traffic that breaks decryption technically, so don’t use the SSL Decryption Exclusion list to exclude this traffic from decryption. Instead, create a policy-based decryption exclusion to identify and control traffic you choose not to decrypt and apply the no-decrypt decryption profile to the policy rule to prevent servers with certificate issues from accessing the network. Policy-based decryption exclusions are only for traffic you choose not to decrypt.
When planning your decryption policy, consider your company’s security compliance rules, computer usage policy, and business goals. Strict controls can impact user experience by preventing access to nonbusiness sites that users could previously access (and which may be required for government or financial institutions). There is always a tradeoff between usability, management overhead, and security. The tighter the decryption policy, the greater the chance that a website will become unreachable, which may result in user complaints and the need to modify the rulebase.
Use complaints as a tool to better understand the traffic on your network. Although a tight decryption policy may initially cause a few user complaints, those complaints can draw your attention to unsanctioned or undesirable websites that are blocked because they use weak algorithms or have certificate issues.
Different groups of users and individuals may require different decryption policy rules, or you may want to apply the same rules to all users. For example, executives may be exempted from decryption policy rules that apply to other employees. You may also want to apply different rules to employee groups, contracts, partners, and guests. Prepare updated legal and HR computer usage policies for distribution to all employees, contractors, partners, guests, and any other network users so that when you roll out decryption, users understand their data can be decrypted and scanned for threats.
How you handle guest users depends on the access they require. Isolate guests from the rest of your network by placing them on a separate VLAN and a separate SSID for wireless access. If guests don’t need to access your corporate network, restrict their access. There will be no need to decrypt their traffic. If guests need to access your corporate network, decrypt their traffic.
  • Enterprises don’t control guest devices. Decrypt guest traffic and subject it to your guest Security policy rules so the NGFW inspects the traffic and prevents threats. To do this, redirect guest users through an Authentication Portal, instruct them how to download and install the CA certificate, and clearly notify guests that their traffic will be decrypted. Include this process in your company’s privacy and computer usage policy.
  • Create separate decryption policy rules and Security policy rules to limit their access to the areas of your network that they need to access.
Decide which devices, websites, and applications to decrypt. Today’s networks support not only corporate devices, but BYOD, mobile, remote-user and other devices, including contractor, partner, and guest devices. Today’s users attempt to access many sites, both sanctioned and unsanctioned, and you should decide how much of that traffic you want to decrypt.
Enterprises don’t control BYOD devices. If you allow BYOD devices on your network, decrypt their traffic and subject it to the same Security policy rules that you apply to other network traffic so the NGFW can inspect the traffic and prevent threats. To do this, redirect BYOD users through an Authentication Portal, instruct them how to download and install the CA certificate, and clearly notify users that their traffic will be decrypted. Educate BYOD users about the process and include it in your company’s privacy and computer usage policy.
Decide what traffic to log, and investigate what traffic you can log. Be aware of local laws regarding data logging and storage, including where you can log and store the data. For example, local laws may prevent the logging and storing of personal information such as health and financial data.
Decide how to handle bad certificates. For example, will you block or allow sessions for which the certificate status is "unknown"? Understanding your approach to bad certificates will help you configure the decryption profiles that you attach to decryption policy rules to control the sessions you allow based on server certificate verification status.

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