ch3: edits

book/source/03-cryptography.md

@@ -5,11 +5,39 @@
 
 - Introduce cryptographic primitives/terms at a very superficial level
 - Introduce visualizations for cryptographic primitives
+- Show example visualizations for operations? (encrypt/decrypt and signing/verification - only if we're going to reuse the visual primitives later)
 ```
 
-## Public-key cryptography
+## (Cryptographic) hash functions
 
-https://en.wikipedia.org/wiki/Public-key_cryptography
+https://en.wikipedia.org/wiki/Cryptographic_hash_function
+
+## Symmetric-key cryptography
+
+[Symmetric-key cryptography](https://en.wikipedia.org/wiki/Symmetric-key_algorithm) uses the same cryptographic key for both encryption and decryption. Symmetric-key cryptographic systems support *encryption/decryption* operations.
+
+Participants in symmetric-key operations need to exchange the shared secret over a secure channel.
+
+```{admonition} TODO
+:class: warning
+
+- visualization? (maybe a black key icon, following wikipedia's example?)
+```
+
+### Symmetric-key cryptography in OpenPGP
+
+Symmetric cryptography is used in OpenPGP as part of a [hybrid cryptosystem](https://en.wikipedia.org/wiki/Hybrid_cryptosystem).
+
+Where symmetric keys are used in OpenPGP, they are referred to as "session keys."
+
+### Authenticated encryption with associated data (AEAD)
+
+
+## Public-key, or asymmetric cryptography
+
+[Public-key cryptography](https://en.wikipedia.org/wiki/Public-key_cryptography) systems use asymmetric pairs of related keys. Public-key cryptographic systems support *encryption/decryption* and *digital signature* operations.
+
+Public-key cryptography doesn't require participants to have pre-arranged a shared secret.
 
 ### Asymmetric cryptographic key pairs
 
@@ -18,17 +46,17 @@ In many places, we'll deal with asymmetric cryptographic key pairs:
 ```{figure} diag/cryptographic_keys.png
 ---
 ---
-A cryptographic keypair
+An asymmetric cryptographic key pair
 ```
 
-A cryptographic key pair consists of a public and a private part. In this document, we'll show the public part of a cryptographic key in green, and the private part in red.
+An asymmetric cryptographic key pair consists of a public and a private part. In this document, we'll show the public part of key pair in green, and the private part in red.
 
 We'll usually visualize cryptographic key pairs in this more compact form:
 
 ```{figure} diag/keypair.png
 ---
 ---
-A cryptographic keypair, more compact representation
+Asymmetric key pair, more compact representation
 ```
 
 Note that in many contexts, only the public part is present (more on that later):
@@ -37,33 +65,17 @@ Note that in many contexts, only the public part is present (more on that later)
 ```{figure} diag/keypair_pub.png
 ---
 ---
-Only the public part of a cryptographic keypair
+Only the public part of an asymmetric key pair
 ```
 
+### Cryptographic digital signatures
+
 ### Public-key cryptography in OpenPGP
 
-OpenPGP makes heavy use of public-key cryptography. However, for historical reasons, OpenPGP uses the terms "public/secret" instead of "public/private."
+OpenPGP makes heavy use of public-key cryptography.
 
-So when reading the RFC, or other documentation, you will encounter the term "secret key," instead of the more common "private key."
+Note that, for historical reasons, OpenPGP often uses the terms "public/secret" instead of "public/private." The OpenPGP RFC and other documentation often use the non-standard term "secret key" instead of the more common "private key."
 
-## Symmetric encryption
+## Hybrid cryptosystems
 
-https://en.wikipedia.org/wiki/Symmetric-key_algorithm
-
-```{admonition} TODO
-:class: warning
-
-- 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
+[Hybrid cryptosystems](https://en.wikipedia.org/wiki/Hybrid_cryptosystem) combine public-key cryptosystems with symmetric-key cryptosystems in a way that makes use of their respective advantages.