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ch3: minor cleanup

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Heiko Schaefer 2023-09-29 19:01:22 +02:00
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book/source/03-cryptography.md
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@ -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.
We'll usually visualize cryptographic key pairs in this more compact form:
```{figure} diag/keypair.png
---
---
Asymmetric key pair, more compact representation
```
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.
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