openpgp-notes/book/source/03-cryptography.md

# 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)

This would be a good place to introduce visualizations for cryptographic primitives
```

## Public-key cryptography

https://en.wikipedia.org/wiki/Public-key_cryptography

### Asymmetric cryptographic key pairs

In many places, we'll deal with asymmetric cryptographic key pairs:

```{figure} diag/cryptographic_keys.png
---
---
A cryptographic keypair
```

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.

We'll usually visualize cryptographic keypairs in this more compact form:

```{figure} diag/keypair.png
---
---
A cryptographic keypair, more compact representation
```

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
```

### 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."

So when reading the RFC, or other documentation, you will encounter the term "secret key," instead of the more common "private key."

### Symmetric encryption

https://en.wikipedia.org/wiki/Symmetric-key_algorithm

[TODO: 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.

## Cryptographic signatures