Provided by: inn2_2.7.3~20250201-1_amd64 
NAME
inn-secrets.conf - Configuration data for InterNetNews secrets
DESCRIPTION
inn-secrets.conf in pathetc is a configuration file containing general secrets used by INN. It was added
in INN 2.7.0 for the implementation of Cancel-Lock. The intent is that new secrets used by INN are added
to that file, and that all secrets currently stored in several other configuration files eventually move
to that file.
The inn-secrets.conf file is not required. It currently only serves the purpose of Cancel-Lock. If not
present or empty, the Cancel-Lock authentication system will just be deactivated for local posts.
This file is intended to be fairly static. Any changes made to it will generally not affect any running
programs until they restart.
Changes in Cancel-Lock secrets will be taken into account when new nnrpd processes are spawned (which
happens each time a reader opens a new connection).
Blank lines and lines starting with a number sign ("#") are ignored. All other lines specify parameters,
and are organized in groups. The general form is:
<group> {
<parameter>: <value>
}
(Any amount of whitespace can be put after the colon and is optional.) If the value contains embedded
whitespace or any of the characters "[]<>{}"\:;", it must be enclosed in double quotes (""). A backslash
("\") can be used to escape quotes and backslashes inside double quotes. <group> and <parameter> are
case-sensitive; "cancels" is not the same as "Cancels" or "CANCELS". (inn-secrets.conf groups and
parameters are generally all in lowercase.)
The two parameters currently defined in this file have as their value a list of strings, that is to say
space-separated elements enclosed in square brackets. Examples follow in the documentation.
PARAMETERS
Cancel-Lock secrets
These secrets are used for the Cancel-Lock authentication system described in RFC 8315. This mechanism
permits verifying that the withdrawal of an article is valid, that is to say the poster, posting agent,
moderator, or injecting agent that processed the original article has requested to withdraw it via the
use of a cancel control article or a Supersedes header field.
You'll need to build INN with version 3.3.0 or later of libcanlock to embed Cancel-Lock support. This
library is available at <https://micha.freeshell.org/libcanlock/>. The "configure" script will
automatically enable Cancel-Lock support if it finds libcanlock; you may have to specify the
--with-canlock option to help "configure" find it.
The "cancels" group is defined as follows (you should naturally use other passwords than the following
ones):
cancels {
canlockadmin: [ "9kc3ZtAACpNZRGtmYiPlbfkDacqNwPbcEfzFodc5X48g" ]
canlockuser: [ "TSrg41qEbp6AyZuQoIIHo6sUzFkBLOocJYN3KsUVdgft" ]
}
If one of the canlockadmin or canlockuser parameters is not an empty list, nnrpd will add information to
every posted article that will permit other news servers to later ensure that an attempt to cancel or
supersede the article is not forged, and really originates from the authenticated original sender or the
administrator of the local server.
If your users are not individually authenticated or identifiable with a unique static IP, you must not
set canlockuser as otherwise anyone would be able to cancel the articles of any other person with the
same assigned identity. If all or only some of your users are individually authenticated or
identifiable, you can set canlockuser and make sure to parameterize addcanlockuser to "none" in all the
access groups in readers.conf that are shared between several different persons with the same identity.
More concretely, for each secret in canlockadmin, nnrpd adds two Base64-encoded hashes to a Cancel-Lock
header field. These hashes are based on the secret and the Message-ID of the article. If this field
already exists, it will just append the Base64-encoded hashes to its end. One hash uses the SHA-1
algorithm (for interoperability reasons as not all news software implement SHA-256), and the other hash
uses the mandatory SHA-256 algorithm per RFC 8315. Besides, nnrpd will similarly add two Base64-encoded
hashes for each secret in canlockuser; these hashes are based on the secret, the identity assigned in
readers.conf to the connection or its static IP (depending on the setting of addcanlockuser), and the
Message-ID of the article.
When a cancel or supersede article is posted by an authenticated user, nnrpd will add to a Cancel-Key
header field two pre-images for each secret in canlockuser. (This is why it is important, if you have
set canlockuser, to parameterize addcanlockuser to "none" in all the access groups in readers.conf not
corresponding to individual persons.) Other news servers can then hash one of these pre-images with
SHA-1 or SHA-256 algorithms (one is enough) and verify that the resulted Base64-encoded hash is the same
as the one present in the Cancel-Lock header field of the original article. (Necessarily, the same
authenticated user on the same local server sent the original article.) When receiving articles with a
Cancel-Key header field (locally or from other peers), innd applies that check to verify the authenticity
of the withdrawal before deciding to honour it.
Naturally, no pre-images for each secret in canlockadmin are added by nnrpd. As these pre-images are not
based on a user name, only the news administrator can generate them (with the gencancel tool shipped with
INN) and then inject the cancel or supersede request with for instance inews. The news administrator is
therefore capable to send authenticated withdrawal requests for articles posted by all the users of his
news server, be they authenticated or not.
After this (little) introduction to explain what Cancel-Lock is for, here are the two relevant
parameters:
canlockadmin
This parameter expects a list of strings. It is unset by default (no admin hashes will be
generated).
If this parameter is not an empty list, each provided secret will be used to generate admin hashes.
To maximize security, secrets should have a length of at least the output size of the hash function
used (32 octets for SHA-256). You can for instance generate a strong secret based on 33 random
octets (so that the last character is not systematically "=", as it happens when Base64-encoding 32
random octets) with:
% openssl rand -base64 33
nfwx6FS+U/dXXXqTOTp1Z5J9glV9UpjyhUcVcsDqXSC8
and use it as follows:
canlockadmin: [ "nfwx6FS+U/dXXXqTOTp1Z5J9glV9UpjyhUcVcsDqXSC8" ]
The purpose of providing several secrets is when you want to rotate secrets. For instance, if your
policy is to change secrets each year, you can use two secrets during a transition period:
canlockadmin: [ "rH5L8geEzkNVvpAZQMJJcd4AYkpSkkx5S/4qewPDA/U="
"nfwx6FS+U/dXXXqTOTp1Z5J9glV9UpjyhUcVcsDqXSC8" ]
Withdrawals of previously posted articles will still work with the old secret (still added to the
Cancel-Key header field).
As all posted articles will have a Cancel-Lock header field with the admin secret, you should also
set canlockuser (and individually authenticate the posters) because otherwise posters may not be able
to withdraw their own articles (unless their posting agents generate Cancel-Lock header fields
themselves with their own secrets).
canlockuser
This parameter expects a list of strings. It is unset by default (no user-specific hashes will be
generated).
The same recommendation of more than 32 random octets applies, and the secrets must not be the same
as canlockadmin.
If this parameter is not an empty list, each provided secret will be used to generate hashes based on
the identity assigned to users by readers.conf or their static IP (depending on the setting of
addcanlockuser). Beware that if your users are not individually authenticated, you must not set
canlockuser as otherwise anyone would be able to cancel the articles of any other person with the
same assigned identity. If needed, you can deactivate the generation of user-specific hashes in
access groups shared between several different persons with the same identity in readers.conf by
setting addcanlockuser to "none" in these access groups (it may for instance be the case for
localhost connections, if some articles are injected with inews from an external source).
When using canlockuser, you should also set canlockadmin because you may otherwise not always be able
to generate the needed hash to cancel an article posted by the users of your news server (notably if
you do not manage to find out the identity a user had when posting the original article).
HISTORY
Documentation written by Julien Elie for InterNetNews.
SEE ALSO
gencancel(1), nnrpd(8), readers.conf(5).
INN 2.7.3 2025-02-21 INN-SECRETS.CONF(5)