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101 lines
3.6 KiB
Markdown
101 lines
3.6 KiB
Markdown
(cyrptography_chapter)=
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# Cryptographic concepts/terms
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```{admonition} TODO
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:class: warning
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- Introduce cryptographic primitives/terms at a very superficial level
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- Introduce visualizations for cryptographic primitives
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- Show example visualizations for operations? (encrypt/decrypt and signing/verification - only if we're going to reuse the visual primitives later)
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```
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## (Cryptographic) hash functions
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https://en.wikipedia.org/wiki/Cryptographic_hash_function
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Note: hashes are sometimes called "digests".
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## Symmetric-key cryptography
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[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.
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Participants in symmetric-key operations need to exchange the shared secret over a secure channel.
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```{admonition} TODO
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:class: warning
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- visualization? (maybe a black key icon, following wikipedia's example?)
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```
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Symmetric-key cryptography is much faster than public-key cryptography. Also, unlike traditional public-key mechanisms, symmetric-key cryptography is quantum-resistant.
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So there is a trade-off: Symmetric-key has major benefits, but exchanging the shared secret is a problem that needs to be solved separately. [Hybrid cryptosystems](hybrid_cryptosystems) are one common approach.
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### Symmetric-key cryptography in OpenPGP
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Symmetric cryptography is used in OpenPGP as part of a [hybrid cryptosystem](https://en.wikipedia.org/wiki/Hybrid_cryptosystem).
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Where symmetric keys are used in OpenPGP, they are referred to as "session keys."
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### Authenticated encryption with associated data (AEAD)
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```{admonition} TODO
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:class: warning
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- AEAD solves the problem of malleability.
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```
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## Public-key, or asymmetric cryptography
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[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.
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Public-key cryptography doesn't require participants to have pre-arranged a shared secret.
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### Asymmetric cryptographic key pairs
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In many places, we'll deal with asymmetric cryptographic key pairs:
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```{figure} diag/cryptographic_keys.png
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---
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---
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An asymmetric cryptographic key pair
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```
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```{admonition} VISUAL
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:class: warning
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- Wiktor notes: red-green color-blindness affects 8,5% of the population.
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- Heiko: maybe use colors + distinct shapes for the two key halves?
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```
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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.
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We'll usually visualize cryptographic key pairs in this more compact form:
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```{figure} diag/keypair.png
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---
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Asymmetric key pair, more compact representation
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```
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Note that in many contexts, only the public part is present (more on that later):
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```{figure} diag/keypair_pub.png
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---
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Only the public part of an asymmetric key pair
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```
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### Cryptographic digital signatures
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### Public-key cryptography in OpenPGP
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OpenPGP makes heavy use of public-key cryptography.
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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."
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(hybrid_cryptosystems)=
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## Hybrid cryptosystems
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[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.
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