vanitasvitae/openpgp-notes
1
0
Fork 0
mirror of https://codeberg.org/openpgp/notes.git synced 2025-09-10 11:49:40 +02:00
Code Issues Projects Releases Packages Wiki Activity

normalize styling of terms

Browse source
This commit is contained in:
Heiko Schaefer 2023-12-11 00:55:39 +01:00
parent b89b8fb086
commit 313285a0e1
No known key found for this signature in database
GPG key ID: DAE9A9050FCCF1EB
1 changed files with 15 additions and 15 deletions
Download patch file Download diff file Expand all files Collapse all files

26
book/source/10-encryption.md
View file

@ -13,12 +13,12 @@ For an in-depth, packet-level view of encrypted data in OpenPGP, see {ref}`zoom_
## Terminology ## Terminology
| Term | Description | | Term | Description |
|------|-------------| |--------------|------------------------------------------------------------------------------------------------------------|
| SEIPD Packet | *Symmetrically Encrypted, Integrity Protected Data* packet; contains the encrypted message payload | | SEIPD Packet | *Symmetrically Encrypted, Integrity Protected Data* packet; contains the encrypted message payload |
| SKESK Packet | *Symmetric-Key-Encrypted Session-Key* packet; contains or provides a passphrase-encrypted Session-Key | | SKESK Packet | *Symmetric-Key Encrypted Session Key* packet; contains or provides a passphrase-encrypted session key |
| PKESK Packet | *Public-Key-Encrypted Session-Key* packet; contains a session-key encrypted using an asymmetric public-key | | PKESK Packet | *Public-Key Encrypted Session Key* packet; contains a session key encrypted using an asymmetric public key |
| Session-Key | Symmetric encryption key, which is either used directly as - or to derive - the Message-Key | | Session Key | Symmetric encryption key, which is either used directly as - or to derive - the message key |
| Message-Key | Symmetric encryption key used to encrypt the contents of the SEIPD packet | | Message Key | Symmetric encryption key used to encrypt the contents of the SEIPD packet |
## High-Level overview of the message encryption process ## High-Level overview of the message encryption process
@ -57,7 +57,7 @@ The typical combination of mechanisms for encryption in OpenPGP is a [hybrid cry
## Encapsulating session keys: PKESK, SKESK ## Encapsulating session keys: PKESK, SKESK
"*ESK" (encrypted session-key) packets are a family of mechanisms for encapsulation of symmetric key material. There are two branches: "*ESK" (encrypted session key) packets are a family of mechanisms for encapsulation of symmetric key material. There are two branches:
- [PKESK](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-public-key-encrypted-sessio): Uses asymmetric OpenPGP key material to protect a session key, and - [PKESK](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-public-key-encrypted-sessio): Uses asymmetric OpenPGP key material to protect a session key, and
- [SKESK](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-symmetric-key-encrypted-ses): Uses passphrases to protect the symmetric key material, instead of OpenPGP asymmetric key material (this is less commonly used). - [SKESK](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-symmetric-key-encrypted-ses): Uses passphrases to protect the symmetric key material, instead of OpenPGP asymmetric key material (this is less commonly used).
@ -66,7 +66,7 @@ An arbitrary number of PKESKs and SKESKs can be used for the same message. It is
### PKESK: Session key encrypted to an asymmetric OpenPGP key ### PKESK: Session key encrypted to an asymmetric OpenPGP key
To encrypt an OpenPGP message for a recipient, the session-key is encrypted to the recipients public key. The resulting encrypted session key is packed into a PKESK packet, which holds essential metadata, like an identifier of the recipients encryption (sub)-key. To encrypt an OpenPGP message for a recipient, the session key is encrypted to the recipients public key. The resulting encrypted session key is packed into a PKESK packet, which holds essential metadata, like an identifier of the recipients encryption (sub)-key.
This procedure is repeated for each recipient of the message, and all resulting PKESK packets are prepended to the SEIPD packet (see below) containing the actual message. This procedure is repeated for each recipient of the message, and all resulting PKESK packets are prepended to the SEIPD packet (see below) containing the actual message.
@ -74,7 +74,7 @@ Typically, the sender would also include themselves as a recipient, in order to
### SKESK: Session key encrypted to a passphrase ### SKESK: Session key encrypted to a passphrase
As an alternative (or augmentation) to PKESK packets, a message can also be encrypted to a symmetric passphrase. This is done using a SKESK packet, which uses an S2K mechanism to derive a symmetric key from a passphrase. This key is either used directly as the session-key, or more commonly, used as a key-encapsulation-key (KEK) to encrypt the session-key. As an alternative (or augmentation) to PKESK packets, a message can also be encrypted to a symmetric passphrase. This is done using a SKESK packet, which uses an S2K mechanism to derive a symmetric key from a passphrase. This key is either used directly as the session key, or more commonly, used as a key-encapsulation-key (KEK) to encrypt the session key.
Also see https://flowcrypt.com/docs/guide/send-and-receive/send-password-protected-emails.html Also see https://flowcrypt.com/docs/guide/send-and-receive/send-password-protected-emails.html
@ -109,7 +109,7 @@ The [version 1 SEIPD](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-
Version 1 SEIPD can only be combined with [version 3 PKESK](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#v3-pkesk) and/or [version 4 SKESK](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#v4-skesk) packets. Version 1 SEIPD can only be combined with [version 3 PKESK](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#v3-pkesk) and/or [version 4 SKESK](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#v4-skesk) packets.
In this version of the SEIPD packet, the session-key is used directly as message-key, meaning the payload is encrypted symmetrically using the session-key. In this version of the SEIPD packet, the session key is used directly as message key, meaning the payload is encrypted symmetrically using the session key.
When communicating with a mix of recipients, some of whose OpenPGP software only supports OpenPGP version 4, then this mechanism must be used. When communicating with a mix of recipients, some of whose OpenPGP software only supports OpenPGP version 4, then this mechanism must be used.
@ -117,7 +117,7 @@ When communicating with a mix of recipients, some of whose OpenPGP software only
:name: fig-encryption-seipdv1-pkesk :name: fig-encryption-seipdv1-pkesk
:alt: Depicts a dotted hexagon labeled "Plaintext", from which a curved arrow passes another dotted hexagon "Session Key" and finally points to a "SEIPDv1" packet. Two more curved arrows originate from the session key and pass Alice' and Bob's encryption key, ending in two PKESK packets. :alt: Depicts a dotted hexagon labeled "Plaintext", from which a curved arrow passes another dotted hexagon "Session Key" and finally points to a "SEIPDv1" packet. Two more curved arrows originate from the session key and pass Alice' and Bob's encryption key, ending in two PKESK packets.
With SEIPDv1, the session-key is directly used as message-key to encrypt the payload With SEIPDv1, the session key is directly used as message key to encrypt the payload
``` ```
(SEIPDv2)= (SEIPDv2)=
@ -130,14 +130,14 @@ v2 SEIPD can only be combined with either [version 6 PKESK](https://www.ietf.org
In version 2 SEIPD, the *session key* is transformed into a *message key*, based on a per-message salt value stored separately in the v2 SEIPD packet. The message key is then used in an AEAD scheme to encrypt the message payload. In version 2 SEIPD, the *session key* is transformed into a *message key*, based on a per-message salt value stored separately in the v2 SEIPD packet. The message key is then used in an AEAD scheme to encrypt the message payload.
```{note} ```{note}
The session-key can use a different symmetric algorithm than the message-key. The session key can use a different symmetric algorithm than the message key.
``` ```
```{figure} drawio/SEIPDv2-PKESK.svg ```{figure} drawio/SEIPDv2-PKESK.svg
:name: fig-encryption-seipdv2-pkesk :name: fig-encryption-seipdv2-pkesk
:alt: TODO :alt: TODO
With SEIPDv2, the message-key is derived from the session-key in an extra step. With SEIPDv2, the message key is derived from the session key in an extra step.
``` ```
This additional step introduces key-separation into the protocol, which protects against certain attacks, such as an [OpenPGP SEIP downgrade attack](https://www.metzdowd.com/pipermail/cryptography/2015-October/026685.html). This additional step introduces key-separation into the protocol, which protects against certain attacks, such as an [OpenPGP SEIP downgrade attack](https://www.metzdowd.com/pipermail/cryptography/2015-October/026685.html).
@ -145,7 +145,7 @@ This additional step introduces key-separation into the protocol, which protects
```{admonition} TODO ```{admonition} TODO
:class: warning :class: warning
Explain, that with SEIPDv2, a session-key can essentially protect more than one message by reusing the same session-key and *ESK packets with a fresh, per-message salt. Explain, that with SEIPDv2, a session key can essentially protect more than one message by reusing the same session key and *ESK packets with a fresh, per-message salt.
This might very well go into the advanced topics section though. This might very well go into the advanced topics section though.
``` ```