ch3: minor cleanup

book/source/03-cryptography.md

@@ -1,5 +1,5 @@
 (cyrptography_chapter)=
-# Cryptographic concepts/terms
+# Cryptographic concepts and terms
 
 ```{admonition} VISUAL
 :class: warning
@@ -24,15 +24,17 @@ Participants in symmetric-key operations need to exchange the shared secret over
 - visualization? (maybe a black key icon, following wikipedia's example?)
 ```
 
-Symmetric-key cryptography is much faster than public-key cryptography. Also, most current symmetric cryptographic algorithms are considered quantum-resistant.
+### Benefits and downsides
 
-So symmetric-key cryptography has major benefits, but exchanging the shared secret is a problem that needs to be solved separately.
+Symmetric-key cryptography has major benefits: it is much faster than public-key cryptography (see below). Also, most current symmetric cryptographic algorithms are considered quantum-resistant.
 
-[Hybrid cryptosystems](hybrid_cryptosystems) are one common approach to leverage the benefits of symmetric-key cryptography, while handling the shared secret with a separate mechanism (using public-key cryptography).
+However, exchanging the required shared secret is a problem that needs to be solved separately.
+
+[Hybrid cryptosystems](hybrid_cryptosystems) (see below) are one common approach to leverage the benefits of symmetric-key cryptography, while handling the shared secret with a separate mechanism (using public-key cryptography).
 
 ### Symmetric-key cryptography in OpenPGP
 
-Symmetric cryptography is used in OpenPGP (as part of a hybrid cryptosystem).
+Symmetric cryptography is used in OpenPGP as part of a hybrid cryptosystem.
 
 Where symmetric keys are used in OpenPGP, they are referred to as "session keys."
 
@@ -40,13 +42,13 @@ Where symmetric keys are used in OpenPGP, they are referred to as "session keys.
 
 [Authenticated encryption](https://en.wikipedia.org/wiki/Authenticated_encryption) is a class of cryptographic schemes that gives additional guarantees besides confidentiality.
 
-In OpenPGP version 6, AEAD is used to solve the problem of "malleability": In past versions of the OpenPGP protocol, some malicious changes to ciphertext were undetectable. With AEAD undetected changes of ciphertext are not possible.
+In OpenPGP version 6, AEAD is used to solve the problem of "malleability": In past versions of the OpenPGP protocol, some malicious changes to ciphertext were undetectable. With AEAD, undetected changes of ciphertext are not possible.
 
 ## 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.
+Public-key cryptography doesn't require participants to pre-arrange a shared secret.
 
 ### Asymmetric cryptographic key pairs
 
@@ -65,19 +67,10 @@ An asymmetric cryptographic key pair
 - Heiko: maybe use colors + distinct shapes for the two key halves?
 ```
 
-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.
+An asymmetric cryptographic key pair consists of a public and a private part. In this document, we'll show the public part of a 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
----
----
-Asymmetric key pair, more compact representation
-```
 
 Note that in many contexts, only the public part is present (more on that later):
 
-
 ```{figure} diag/keypair_pub.png
 ---
 ---
@@ -88,7 +81,9 @@ Only the public part of an asymmetric key pair
 
 OpenPGP makes heavy use of public-key cryptography, both for encryption and signing operations.
 
-Note that, for historical reasons, OpenPGP often uses the terms "public/secret key" instead of "public/private key." The OpenPGP RFC and other documentation often use the non-standard term "secret key" instead of the more common "private key."
+Note that, for historical reasons, the OpenPGP RFC and other documentation often use the non-standard term "secret key" instead of the more common "private key."
+
+So in OpenPGP, the pair of terms "public/secret key" is sometimes used instead of the more common "public/private key."
 
 ### Cryptographic digital signatures
 

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