diff --git a/book/source/03-cryptography.md b/book/source/03-cryptography.md
index 0cbe953..29a6398 100644
--- a/book/source/03-cryptography.md
+++ b/book/source/03-cryptography.md
@@ -1,9 +1,10 @@
 # Cryptographic concepts/terms
 
-```
-Lars suggests that we should have a chapter where we introduce cryptographic terms that we use, and give short definitions (without getting into how specific algorithms work)
+```{admonition} TODO
+:class: warning
 
-This would be a good place to introduce visualizations for cryptographic primitives
+- Introduce cryptographic primitives/terms at a very superficial level
+- Introduce visualizations for cryptographic primitives
 ```
 
 ## Public-key cryptography
@@ -45,17 +46,24 @@ OpenPGP makes heavy use of public-key cryptography. However, for historical reas
 
 So when reading the RFC, or other documentation, you will encounter the term "secret key," instead of the more common "private key."
 
-### Symmetric encryption
+## Symmetric encryption
 
 https://en.wikipedia.org/wiki/Symmetric-key_algorithm
 
-[TODO: visualization?]
+```{admonition} TODO
+:class: warning
 
-#### Symmetric cryptography in OpenPGP
+- visualization?
+```
+
+### Symmetric cryptography in OpenPGP
 
 Symmetric encryption is a core concept in OpenPGP. It usually comes up involving the term "session key."
 
 "Session keys" in OpenPGP are symmetric cryptographic keys.
 
+## Hashing
+
 ## Cryptographic signatures
 
+## AEAD
diff --git a/book/source/05-private.md b/book/source/05-private.md
index f4c11a7..ae4d001 100644
--- a/book/source/05-private.md
+++ b/book/source/05-private.md
@@ -1,7 +1,9 @@
 (private_key_chapter)=
 # Private keys
 
-```
+```{admonition} TODO
+:class: warning
+
 - Consistently consider private key material as a separate thing from Certificates? (like in pkcs#11?)
 ```
 
diff --git a/book/source/07-signing_data.md b/book/source/07-signing_data.md
index 94753b5..7ec8512 100644
--- a/book/source/07-signing_data.md
+++ b/book/source/07-signing_data.md
@@ -1,2 +1,13 @@
 (signing_data)=
 # Signatures over data
+
+```{admonition} TODO
+:class: warning
+
+Add content, including:
+
+- Signature of a binary document
+
+- Signature of a canonical text document
+  - "The signature is calculated over the text data with its line endings converted to `<CR><LF>`"
+```
diff --git a/book/source/08-signature_internals.md b/book/source/08-signature_internals.md
index 29658bc..f9f2234 100644
--- a/book/source/08-signature_internals.md
+++ b/book/source/08-signature_internals.md
@@ -1,6 +1,8 @@
 # Signature "internals"
 
-```
+```{admonition} TODO
+:class: warning
+
   - Subpackets and how to make sense of them
   - "Negotiating" signature hash algorithm based on recipients preference subpackets
   - Explore viability of having multiple signatures, e.g. v4+v6?
diff --git a/book/source/11-decryption.md b/book/source/11-decryption.md
index 053af88..363bb07 100644
--- a/book/source/11-decryption.md
+++ b/book/source/11-decryption.md
@@ -1,7 +1,9 @@
 (decryption_chapter)=
 # Decryption
 
-```
+```{admonition} TODO
+:class: warning
+
   - using expired certificate?
   - using revoked certificate?
   - using expired subkey?
diff --git a/book/source/15-migration.md b/book/source/15-migration.md
index 83f1d6c..9bb57a5 100644
--- a/book/source/15-migration.md
+++ b/book/source/15-migration.md
@@ -1,5 +1,7 @@
 # Migration from v4 to v6
 
-```
+```{admonition} TODO
+:class: warning
+
 Also see: https://wiki.gnupg.org/OpenPGPEmailSummit202305Notes
 ```
diff --git a/book/source/16-policy.md b/book/source/16-policy.md
index 60e8177..d85f4f4 100644
--- a/book/source/16-policy.md
+++ b/book/source/16-policy.md
@@ -1,6 +1,8 @@
 # Algorithms and Policy
 
-```
+```{admonition} TODO
+:class: warning
+
   - What algorithms are trustworthy? -> Depend on regulatory bodies like the BSI?
   - How to decide, when to deprecate / reject algorithms (how to be competent)
   - Transitioning from one set of algorithms to another (Interoperability)