diff --git a/book/source/10-encryption.md b/book/source/10-encryption.md
index 0d0b1c5..13b41b1 100644
--- a/book/source/10-encryption.md
+++ b/book/source/10-encryption.md
@@ -33,10 +33,18 @@ Core concept:
 
 ### Implications of how a recipient cert is "addressed" (fingerprint/key-ID vs. user-ID) (preferences, expiration, revocation)
 
+### AEAD modes: GCM
+
+```{admonition} TODO
+:class: warning
+
+Produce text around discussion: https://mailarchive.ietf.org/arch/msg/openpgp/ZTYD5VJsG1k2jJBbn5zIAf5o7d4/
+```
+
 ## Zooming in: Packet structure
 
 ### Encryption yields a 'wrapped' openpgp packet stream
 
 ### SKESK
 
-Also see https://flowcrypt.com/docs/guide/send-and-receive/send-password-protected.html
\ No newline at end of file
+Also see https://flowcrypt.com/docs/guide/send-and-receive/send-password-protected.html