Merge pull request #657 from tschmidtb51/cdn

CDN

csaf_2.0/guidance/cdn.md

@@ -0,0 +1,59 @@
+# CSAF and Content Delivery Networks (CDNs)
+
+If you want to use a CDN to provide your CSAF files, please find some remarks below:
+
+- **Activate caching**: Most files are more or less static - activate caching to minimize risk for (D)DoS.
+- **Include path exemption**: The path `.well-known/csaf/` and potentially `.well-known/security.txt` need to be accessible for all HTTP-clients (also those that are usually detected as bots).
+
+  *Specifically, at least the files in this path ending on `.json`, `.asc`, `.sha256` and `.sha512` should be excluded.*
+- **Flush cache when updating files**: When new files are written or old files updated, the cache must be updated. Usually, this can be done through the API the CDN provides. Instead of flushing the whole cache (easy way), a more precise way can be used as files that need to be updated in the cache depend on the distribution method:
+
+  **Directory-based distribution:**
+
+  ```
+  <path-to-updated-CSAF-document>.json
+  <path-to-updated-CSAF-document>.json.asc
+  <path-to-updated-CSAF-document>.json.sha256
+  <path-to-updated-CSAF-document>.json.sha512
+  <path-of-index>.txt
+  <path-of-changes>.csv
+  ```
+
+  *Example:*
+
+  The CSAF advisory `ESA-2023-31816` was changed. Consequently, the following files in the cache need to be updated.
+
+  ```
+  .well-known/csaf/white/2023/esa-2023-31816.json
+  .well-known/csaf/white/2023/esa-2023-31816.json.asc
+  .well-known/csaf/white/2023/esa-2023-31816.json.sha256
+  .well-known/csaf/white/2023/esa-2023-31816.json.sha512
+  .well-known/csaf/white/index.txt
+  .well-known/csaf/white/changes.csv
+  ```
+
+  **ROLIE-based distribution:**
+
+  ```
+  <path-to-updated-CSAF-document>.json
+  <path-to-updated-CSAF-document>.json.asc
+  <path-to-updated-CSAF-document>.json.sha256
+  <path-to-updated-CSAF-document>.json.sha512
+  <path-of-ROLIE-feed>.json
+  <path-of-ROLIE-categories>.json
+  <path-of-ROLIE-services>.json
+  ```
+
+  *Example:*
+
+  The CSAF advisory `ESA-2023-31816` was changed. Consequently, the following files in the cache need to be updated.
+
+  ```
+  .well-known/csaf/white/2023/esa-2023-31816.json
+  .well-known/csaf/white/2023/esa-2023-31816.json.asc
+  .well-known/csaf/white/2023/esa-2023-31816.json.sha256
+  .well-known/csaf/white/2023/esa-2023-31816.json.sha512
+  .well-known/csaf/white/csaf-feed-tlp-white.json
+  .well-known/csaf/white/csaf-categories-tlp-white.json
+  .well-known/csaf/service.json
+  ```

csaf_2.0/guidance/faq.md

@@ -48,6 +48,10 @@ Future versions of [CSAF will support TLP v2](https://github.com/oasis-tcs/csaf/
 
 CSAF lister and CSAF aggregator choose on their own which producing parties they add to their lists. Please reach out to the CSAF lister or CSAF aggregator in question. Their contact details are available in the metadata of the list.
 
+### I want to use a Content Delivery Network (CDN) to distribute CSAF files. What do I need to consider?
+
+Please see our advise on [CDNs](./cdn.md).
+
 ### Where can I find a list of all parties that produce CSAF?
 
 Currently, there is no such list available. However, [BSI hosts a list with metadata of known parties](https://wid.cert-bund.de/.well-known/csaf-aggregator/aggregator.json) that produce CSAF files and distribute them in a way that they are automatically retrievable. This list is called a CSAF lister.