notmuch/doc/man7/notmuch-properties.rst
Daniel Kahn Gillmor 29648a137c crypto: actually stash session keys when decrypt=true
If you're going to store the cleartext index of an encrypted message,
in most situations you might just as well store the session key.
Doing this storage has efficiency and recoverability advantages.

Combined with a schedule of regular OpenPGP subkey rotation and
destruction, this can also offer security benefits, like "deletable
e-mail", which is the store-and-forward analog to "forward secrecy".

But wait, i hear you saying, i have a special need to store cleartext
indexes but it's really bad for me to store session keys!  Maybe
(let's imagine) i get lots of e-mails with incriminating photos
attached, and i want to be able to search for them by the text in the
e-mail, but i don't want someone with access to the index to be
actually able to see the photos themselves.

Fret not, the next patch in this series will support your wacky
uncommon use case.
2017-12-08 08:08:47 -04:00

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==================
notmuch-properties
==================
SYNOPSIS
========
**notmuch** **count** **property:**\ <*key*>=<*value*>
**notmuch** **search** **property:**\ <*key*>=<*value*>
**notmuch** **show** **property:**\ <*key*>=<*value*>
**notmuch** **reindex** **property:**\ <*key*>=<*value*>
**notmuch** **tag** +<*tag*> **property:**\ <*key*>=<*value*>
**notmuch** **dump** **--include=properties**
**notmuch** **restore** **--include=properties**
DESCRIPTION
===========
Several notmuch commands can search for, modify, add or remove
properties associated with specific messages. Properties are
key/value pairs, and a message can have more than one key/value pair
for the same key.
While users can select based on a specific property in their search
terms with the prefix **property:**, the notmuch command-line
interface does not provide mechanisms for modifying properties
directly to the user.
Instead, message properties are expected to be set and used
programmatically, according to logic in notmuch itself, or in
extensions to it.
Extensions to notmuch which make use of properties are encouraged to
report the specific properties used to the upstream notmuch project,
as a way of avoiding collisions in the property namespace.
CONVENTIONS
===========
Any property with a key that starts with "index." will be removed (and
possibly re-set) upon reindexing (see **notmuch-reindex(1)**).
MESSAGE PROPERTIES
==================
The following properties are set by notmuch internally in the course
of its normal activity.
**index.decryption**
If a message contains encrypted content, and notmuch tries to
decrypt that content during indexing, it will add the property
``index.decryption=success`` when the cleartext was successfully
indexed. If notmuch attempts to decrypt any part of a message
during indexing and that decryption attempt fails, it will add the
property ``index.decryption=failure`` to the message.
Note that it's possible for a single message to have both
``index.decryption=success`` and ``index.decryption=failure``.
Consider an encrypted e-mail message that contains another
encrypted e-mail message as an attachment -- if the outer message
can be decrypted, but the attached part cannot, then both
properties will be set on the message as a whole.
If notmuch never tried to decrypt an encrypted message during
indexing (which is the default, see ``index.decrypt`` in
**notmuch-config(1)**), then this property will not be set on that
message.
**session-key**
When **notmuch-show(1)** or **nomtuch-reply** encounters a message
with an encrypted part, if notmuch finds a ``session-key``
property associated with the message, it will try that stashed
session key for decryption.
If you do not want to use any stashed session keys that might be
present, you should pass those programs ``--decrypt=false``.
Using a stashed session key with "notmuch show" will speed up
rendering of long encrypted threads. It also allows the user to
destroy the secret part of any expired encryption-capable subkey
while still being able to read any retained messages for which
they have stashed the session key. This enables truly deletable
e-mail, since (once the session key and asymmetric subkey are both
destroyed) there are no keys left that can be used to decrypt any
copy of the original message previously stored by an adversary.
However, access to the stashed session key for an encrypted message
permits full byte-for-byte reconstruction of the cleartext
message. This includes attachments, cryptographic signatures, and
other material that cannot be reconstructed from the index alone.
See ``index.decrypt`` in **notmuch-config(1)** for more
details about how to set notmuch's policy on when to store session
keys.
The session key should be in the ASCII text form produced by
GnuPG. For OpenPGP, that consists of a decimal representation of
the hash algorithm used (identified by number from RFC 4880,
e.g. 9 means AES-256) followed by a colon, followed by a
hexadecimal representation of the algorithm-specific key. For
example, an AES-128 key might be stashed in a notmuch property as:
``session-key=7:14B16AF65536C28AF209828DFE34C9E0``.
SEE ALSO
========
**notmuch(1)**,
**notmuch-config(1)**,
**notmuch-dump(1)**,
**notmuch-insert(1)**,
**notmuch-new(1)**,
**notmuch-reindex(1)**,
**notmuch-reply(1)**,
**notmuch-restore(1)**,
**notmuch-show(1)**,
***notmuch-search-terms(7)**