Provided by: biboumi_7.2-1_amd64 
NAME
biboumi - XMPP gateway to IRC
Description
Biboumi is an XMPP gateway that connects to IRC servers and translates between the two protocols. It can
be used to access IRC channels using any XMPP client as if these channels were XMPP MUCs.
Synopsis
biboumi [config_filename]
Options
Available command line options:
config_filename
Specify the file to read for configuration. See the Configuration () section for more details on its
content.
Configuration
The configuration file uses a simple format of the form option=value.
The values from the configuration file can be overridden by environment variables, with the name all in
upper case and prefixed with "BIBOUMI ()". For example, if the environment contains
“BIBOUMI_PASSWORD=blah", this will override the value of the “password” option in the configuration file.
Sending SIGUSR1 or SIGUSR2 (see kill(1)) to the process will force it to re-read the configuration and
make it close and re-open the log files. You can use this to change any configuration option at runtime,
or do a log rotation.
Here is a description of every possible option:
hostname
Mandatory. The hostname served by the XMPP gateway. This domain must be configured in the XMPP server
as an external component. See the manual for your XMPP server for more information. For prosody, see
<http://prosody.im/doc/components#adding_an_external_component>
password
Mandatory. The password used to authenticate the XMPP component to your XMPP server. This password must
be configured in the XMPP server, associated with the external component on hostname.
xmpp_server_ip
The IP address to connect to the XMPP server on. The connection to the XMPP server is unencrypted, so
the biboumi instance and the server should normally be on the same host. The default value is 127.0.0.1.
port
The TCP port to use to connect to the local XMPP component. The default value is 5347.
db_name
The name of the database to use. This option can only be used if biboumi has been compiled with a
database support (Sqlite3 and/or PostgreSQL). If the value begins with the postgresql scheme,
“postgresql://” or “postgres://”, then biboumi will try to connect to the PostgreSQL database specified
by the URI. See <https://www.postgresql.org/docs/current/static/libpq-connect.html#idm46428693970032>
for all possible values. For example the value could be “postgresql://user:<secret@localhost>”. If the
value does not start with the postgresql scheme, then it specifies a filename that will be opened with
Sqlite3. For example the value could be “/var/lib/biboumi/biboumi.sqlite”.
admin
The bare JID of the gateway administrator. This JID will have more privileges than other standard users,
for example some administration ad-hoc commands will only be available to that JID.
fixed_irc_server
If this option contains the hostname of an IRC server (for example irc.example.org), then biboumi will
enforce the connexion to that IRC server only. This means that a JID like #chan@biboumi.example.com must
be used instead of #chan%irc.example.org@biboumi.example.com. In that mode, the virtual channel (see
Connect to an IRC server ()) is not available. The % character loses any meaning in the JIDs. It can
appear in the JID but will not be interpreted as a separator (thus the JID
#channel%hello@biboumi.example.com points to the channel named #channel%hello on the configured IRC
server) This option can for example be used by an administrator that just wants to let their users join
their own IRC server using an XMPP client, while forbidding access to any other IRC server.
persistent_by_default
If this option is set to true, all rooms will be persistent by default: the value of the “persistent”
option in the global configuration of each user will be “true”, but the value of each individual room
will still default to false. This means that a user just needs to change the global “persistent”
configuration option to false in order to override this.
If it is set to false (the default value), all rooms are not persistent by default.
Each room can be configured individually by each user, to override this default value. See Ad-hoc
commands ().
realname_customization
If this option is set to “false” (default is “true”), the users will not be able to use the ad-hoc
commands that lets them configure their realname and username.
realname_from_jid
If this option is set to “true”, the realname and username of each biboumi user will be extracted from
their JID. The realname is their bare JID, and the username is the node-part of their JID. Note that if
realname_customization is “true”, each user will still be able to customize their realname and username,
this option just decides the default realname and username.
If this option is set to “false” (the default value), the realname and username of each user will be set
to the nick they used to connect to the IRC server.
webirc_password
Configure a password to be communicated to the IRC server, as part of the WEBIRC message (see
<https://kiwiirc.com/docs/webirc>). If this option is set, an additional DNS resolution of the hostname
of each XMPP server will be made when connecting to an IRC server.
log_file
A filename into which logs are written. If none is provided, the logs are written on standard output.
log_level
Indicate what type of log messages to write in the logs. Value can be from 0 to 3. 0 is debug, 1 is
info, 2 is warning, 3 is error. The default is 0, but a more practical value for production use is 1.
ca_file
Specifies which file should be used as the list of trusted CA when negociating a TLS session. By default
this value is unset and biboumi tries a list of well-known paths.
outgoing_bind
An address (IPv4 or IPv6) to bind the outgoing sockets to. If no value is specified, it will use the one
assigned by the operating system. You can for example use outgoing_bind=192.168.1.11 to force biboumi to
use the interface with this address. Note that this is only used for connections to IRC servers.
identd_port
The TCP port on which to listen for identd queries. The default is the standard value: 113. To be able
to listen on this privileged port, biboumi needs to have certain capabilities: on linux, using systemd,
this can be achieved by adding AmbientCapabilities=CAP_NET_BIND_SERVICE to the unit file. On other
systems, other solutions exist, like the portacl module on FreeBSD.
If biboumi's identd server is properly started, it will receive queries from the IRC servers asking for
the “identity” of each IRC connection made to it. Biboumi will answer with a hash of the JID that made
the connection. This is useful for the IRC server to be able to distinguish the different users, and be
able to deal with the absuses without having to simply ban the IP. Without this identd server,
moderation is a lot harder, because all the different users of a single biboumi instance all share the
same IP, and they can't be distinguished by the IRC servers.
policy_directory
A directory that should contain the policy files, used to customize Botan's behaviour when negociating
the TLS connections with the IRC servers. If not specified, the directory is the one where biboumi's
configuration file is located: for example if biboumi reads its configuration from
/etc/biboumi/biboumi.cfg, the policy_directory value will be /etc/biboumi.
TLS configuration
Various settings of the TLS connections can be customized using policy files. The files should be
located in the directory specified by the configuration option policy_directory (). When attempting to
connect to an IRC server using TLS, biboumi will use Botan's default TLS policy, and then will try to
load some policy files to override the values found in these files. For example, if policy_directory is
/etc/biboumi, when trying to connect to irc.example.com, biboumi will try to read
/etc/biboumi/policy.txt, use the values found to override the default values, then it will try to read
/etc/biboumi/irc.example.com.policy.txt and re-override the policy with the values found in this file.
The policy.txt file applies to all the connections, and irc.example.policy.txt will only apply (in
addition to policy.txt) when connecting to that specific server.
To see the list of possible options to configure, refer to Botan's TLS documentation
(https://botan.randombit.net/manual/tls.html#tls-policies).
By default, biboumi provides a few policy files, to work around some issues found with a few well-known
IRC servers.
Usage
Biboumi acts as a server, it should be run as a daemon that lives in the background for as long as it is
needed. Note that biboumi does not daemonize itself, this task should be done by your init system
(SysVinit, systemd, upstart).
When started, biboumi connects, without encryption (see Security ()), to the local XMPP server on the
port 5347 and authenticates with the provided password. Biboumi then serves the configured hostname:
this means that all XMPP stanza with a to JID on that domain will be forwarded to biboumi by the XMPP
server, and biboumi will only send messages coming from that hostname.
When a user joins an IRC channel on an IRC server (see Join an IRC channel ()), biboumi connects to the
remote IRC server, sets the user's nick as requested, and then tries to join the specified channel. If
the same user subsequently tries to connect to an other channel on the same server, the same IRC
connection is used. If, however, an other user wants to join an IRC channel on that same IRC server,
biboumi opens a new connection to that server. Biboumi connects once to each IRC server, for each user
on it.
Additionally, if one user is using more than one clients (with the same bare JID), they can join the same
IRC channel (on the same server) behind one single nickname. Biboumi will forward all the messages (the
channel ones and the private ones) and the presences to all the resources behind that nick. There is no
need to have multiple nicknames and multiple connections to be able to take part in a conversation (or
idle) in a channel from a mobile client while the desktop client is still connected, for example.
To cleanly shutdown the component, send a SIGINT or SIGTERM signal to it. It will send messages to all
connected IRC and XMPP servers to indicate a reason why the users are being disconnected. Biboumi exits
when the end of communication is acknowledged by all IRC servers. If one or more IRC servers do not
respond, biboumi will only exit if it receives the same signal again or if a 2 seconds delay has passed.
Addressing
IRC entities are represented by XMPP JIDs. The domain part of the JID is the domain served by biboumi
(the part after the @, biboumi.example.com in the examples), and the local part (the part before the @)
depends on the concerned entity.
IRC channels and IRC users have a local part formed like this: name % irc_server.
name can be a channel name or an user nickname. The distinction between the two is based on the first
character: by default, if the name starts with '#' or '&' (but this can be overridden by the server,
using the ISUPPORT extension) then it's a channel name, otherwise this is a nickname.
As a special case, the channel name can also be empty (for example %irc.example.com), in that case this
represents the virtual channel provided by biboumi. See Connect to an IRC server () for more details.
There is two ways to address an IRC user, using a local part like this: nickname % irc_server or by using
the in-room address of the participant, like this: channel_name % irc_server @ biboumi.example.com /
Nickname
The second JID is available only to be compatible with XMPP clients when the user wants to send a private
message to the participant Nickname in the room channel_name%irc_server@biboumi.example.com.
On XMPP, the node part of the JID can only be lowercase. On the other hand, IRC nicknames are
case-insensitive, this means that the nicknames toto, Toto, tOtO and TOTO all represent the same IRC
user. This means you can talk to the user toto, and this will work.
Also note that some IRC nicknames or channels may contain characters that are not allowed in the local
part of a JID (for example '@'). If you need to send a message to a nick containing such a character,
you can use a jid like %irc.example.com@biboumi.example.com/AnnoyingNickn@me, because the JID
AnnoyingNickn@me%irc.example.com@biboumi.example.com would not work. And if you need to address a
channel that contains such invalid characters, you have to use jid-escaping
(http://www.xmpp.org/extensions/xep-0106.html#escaping), and replace each of these characters with their
escaped version, for example to join the channel #b@byfoot, you need to use the following JID:
#b\40byfoot%irc.example.com@biboumi.example.com.
Examples:
• #foo%irc.example.com@biboumi.example.com is the #foo IRC channel, on the irc.example.com IRC server,
and this is served by the biboumi instance on biboumi.example.com
• toto%irc.example.com@biboumi.example.com is the IRC user named toto, or TotO, etc.
• irc.example.com@biboumi.example.com is the IRC server irc.example.com.
• %irc.example.com@biboumi.example.com is the virtual channel provided by biboumi, for the IRC server
irc.example.com.
Note: Some JIDs are valid but make no sense in the context of biboumi:
• #test%@biboumi.example.com, or any other JID that does not contain an IRC server is invalid. Any
message to that kind of JID will trigger an error, or will be ignored.
If compiled with Libidn, an IRC channel participant has a bare JID representing the “hostname” provided
by the IRC server. This JID can only be used to set IRC modes (for example to ban a user based on its
IP), or to identify user. It cannot be used to contact that user using biboumi.
Join an IRC channel
To join an IRC channel #foo on the IRC server irc.example.com, join the XMPP MUC
#foo%irc.example.com@biboumi.example.com.
Connect to an IRC server
The connection to the IRC server is automatically made when the user tries to join any channel on that
IRC server. The connection is closed whenever the last channel on that server is left by the user. To
be able to stay connected to an IRC server without having to be in a real IRC channel, biboumi provides a
virtual channel on the jid %irc.example.com@biboumi.example.com. For example if you want to join the
channel #foo on the server irc.example.com, but you need to authenticate to a bot of the server before
you're allowed to join it, you can first join the room %irc.example.com@biboumi.example.com (this will
effectively connect you to the IRC server without joining any channel), then send your authentication
message to the user bot%irc.example.com@biboumi.example.com and finally join the room
#foo%irc.example.com@biboumi.example.com.
Roster
You can add some JIDs provided by biboumi into your own roster, to receive presence from them. Biboumi
will always automatically accept your requests.
Biboumi's JID
By adding the component JID into your roster, the user will receive an available presence whenever it is
started, and an unavailable presence whenever it is being shutdown. This is useful to quickly view if
that biboumi instance is started or not.
IRC server JID
These presence will appear online in the user's roster whenever they are connected to that IRC server
(see Connect to an IRC server () for more details). This is useful to keep track of which server an user
is connected to: this is sometimes hard to remember, when they have many clients, or if they are using
persistent channels.
Channel messages
On XMPP, unlike on IRC, the displayed order of the messages is the same for all participants of a MUC.
Biboumi can not however provide this feature, as it cannot know whether the IRC server has received and
forwarded the messages to other users. This means that the order of the messages displayed in your XMPP
client may not be the same as the order on other IRC users'.
History
Public channel messages are saved into archives, inside the database, unless the record_history option is
set to false by that user (see Ad-hoc commands ()). Private messages (messages that are sent directly to
a nickname, not a channel) are never stored in the database.
A channel history can be retrieved by using Message archive management (MAM)
(https://xmpp.org/extensions/xep-0313.htm) on the channel JID. The results can be filtered by start and
end dates.
When a channel is joined, if the client doesn't specify any limit, biboumi sends the max_history_length
last messages found in the database as the MUC history. If a client wants to only use MAM for the
archives (because it's more convenient and powerful), it should request to receive no history by using an
attribute maxchars='0' or maxstanzas='0' as defined in XEP 0045, and do a proper MAM request instead.
Note: the maxchars attribute is ignored unless its value is exactly 0. Supporting it properly would be
very hard and would introduce a lot of complexity for almost no benefit.
For a given channel, each user has her or his own archive. The content of the archives are never shared,
and thus a user can not use someone else's archive to get the messages that they didn't receive when they
were offline. Although this feature would be very convenient, this would introduce a very important
privacy issue: for example if a biboumi gateway is used by two users, by querying the archive one user
would be able to know whether or not the other user was in a room at a given time.
List channels
You can list the IRC channels on a given IRC server by sending an XMPP disco items request on the IRC
server JID. The number of channels on some servers is huge so the result stanza may be very big, unless
your client supports result set management (XEP 0059)
Nicknames
On IRC, nicknames are server-wide. This means that one user only has one single nickname at one given
time on all the channels of a server. This is different from XMPP where a user can have a different nick
on each MUC, even if these MUCs are on the same server.
This means that the nick you choose when joining your first IRC channel on a given IRC server will be
your nickname in all other channels that you join on that same IRC server. If you explicitely change
your nickname on one channel, your nickname will be changed on all channels on the same server as well.
Joining a new channel with a different nick, however, will not change your nick. The provided nick will
be ignored, in order to avoid changing your nick on the whole server by mistake. If you want to have a
different nickname in the channel you're going to join, you need to do it explicitly with the NICK
command before joining the channel.
Private messages
Private messages are handled differently on IRC and on XMPP. On IRC, you talk directly to one
server-user: toto on the channel #foo is the same user as toto on the channel #bar (as long as these two
channels are on the same IRC server). By default you will receive private messages from the “global”
user (aka <nickname%irc.example.com@biboumi.example.com>), unless you previously sent a message to an
in-room participant (something like #<test%irc.example.com@biboumi.example.com/nickname>), in which case
future messages from that same user will be received from that same “in-room” JID.
Notices
Notices are received exactly like private messages. It is not possible to send a notice.
Topic
The topic can be set and retrieved seemlessly. The unique difference is that if an XMPP user tries to
set a multiline topic, every line return (\n) will be replaced by a space, because the IRC server
wouldn't accept it.
Invitations
If the invited JID is a user JID served by this biboumi instance, it will forward the invitation to the
target nick, over IRC. Otherwise, the mediated instance will directly be sent to the invited JID, over
XMPP.
Example: if the user wishes to invite the IRC user “FooBar” into a room, they can invite one of the
following “JIDs” (one of them is not a JID, actually):
• <foobar%anything@biboumi.example.com>
• <anything@biboumi.example.com/FooBar>
• FooBar
(Note that the “anything” parts are simply ignored because they carry no additional meaning for biboumi:
we already know which IRC server is targeted using the JID of the target channel.)
Otherwise, any valid JID can be used, to invite any XMPP user.
Kicks and bans
Kicks are transparently translated from one protocol to another. However banning an XMPP participant has
no effect. To ban an user you need to set a mode +b on that user nick or host (see IRC modes ()) and
then kick it.
Encoding
On XMPP, the encoding is always UTF-8, whereas on IRC the encoding of each message can be anything.
This means that biboumi has to convert everything coming from IRC into UTF-8 without knowing the encoding
of the received messages. To do so, it checks if each message is UTF-8 valid, if not it tries to convert
from iso_8859-1 (because this appears to be the most common case, at least on the channels I visit) to
UTF-8. If that conversion fails at some point, a placeholder character '�' is inserted to indicate this
decoding error.
Messages are always sent in UTF-8 over IRC, no conversion is done in that direction.
IRC modes
One feature that doesn't exist on XMPP but does on IRC is the modes. Although some of these modes have a
correspondance in the XMPP world (for example the +o mode on a user corresponds to the moderator role in
XMPP), it is impossible to map all these modes to an XMPP feature. To circumvent this problem, biboumi
provides a raw notification when modes are changed, and lets the user change the modes directly.
To change modes, simply send a message starting with “/mode” followed by the modes and the arguments you
want to send to the IRC server. For example “/mode +aho louiz”. Note that your XMPP client may
interprete messages begining with “/” like a command. To actually send a message starting with a slash,
you may need to start your message with “//mode” or “/say /mode”, depending on your client.
When a mode is changed, the user is notified by a message coming from the MUC bare JID, looking like
“Mode #foo [+ov] [toto tutu]”. In addition, if the mode change can be translated to an XMPP feature, the
user will be notified of this XMPP event as well. For example if a mode “+o toto” is received, then
toto's role will be changed to moderator. The mapping between IRC modes and XMPP features is as follow:
+q Sets the participant's role to moderator and its affiliation to owner.
+a Sets the participant's role to moderator and its affiliation to owner.
+o Sets the participant's role to moderator and its affiliation to admin.
+h Sets the participant's role to moderator and its affiliation to member.
+v Sets the participant's role to participant and its affiliation to member.
Similarly, when a biboumi user changes some participant's affiliation or role, biboumi translates that in
an IRC mode change.
Affiliation set to none
Sets mode to -vhoaq
Affiliation set to member
Sets mode to +v-hoaq
Role set to moderator
Sets mode to +h-oaq
Affiliation set to admin
Sets mode to +o-aq
Affiliation set to owner
Sets mode to +a-q
Ad-hoc commands
Biboumi supports a few ad-hoc commands, as described in the XEP 0050. Different ad-hoc commands are
available for each JID type.
On the gateway itself (e.g on the JID biboumi.example.com):
• ping: Just respond “pong”
• hello: Provide a form, where the user enters their name, and biboumi responds with a nice greeting.
• disconnect-user: Only available to the administrator. The user provides a list of JIDs, and a quit
message. All the selected users are disconnected from all the IRC servers to which they were
connected, using the provided quit message. Sending SIGINT to biboumi is equivalent to using this
command by selecting all the connected JIDs and using the “Gateway shutdown” quit message, except that
biboumi does not exit when using this ad-hoc command.
• disconnect-from-irc-servers: Disconnect a single user from one or more IRC server. The user is
immediately disconnected by closing the socket, no message is sent to the IRC server, but the user is
of course notified with an XMPP message. The administrator can disconnect any user, while the other
users can only disconnect themselves.
• configure: Lets each user configure some options that applies globally. The provided configuration
form contains these fields: * Record History: whether or not history messages should be saved in the
database. * Max history length: The maximum number of lines in the history that the server is allowed
to send when joining a channel.
• Persistent: Overrides the value specified in each individual channel. If this option is set
to true, all channels are persistent, whether or not their specific value is true or false.
This option is true by default for everyone if the persistent_by_default configuration option
is true, otherwise it's false. See below for more details on what a persistent channel is.
This value is
On a server JID (e.g on the JID
<chat.freenode.org@biboumi.example.com>)
• configure: Lets each user configure some options that applies to the concerned IRC server. The
provided configuration form contains these fields: * Realname: The customized “real name” as it will
appear on the user's whois. This option is not available if biboumi is configured with
realname_customization to false. * Username: The “user” part in your user@host. This option is not
available if biboumi is configured with realname_customization to false. * In encoding: The incoming
encoding. Any received message that is not proper UTF-8 will be converted will be converted from the
configured In encoding into UTF-8. If the conversion fails at some point, some characters will be
replaced by the placeholders. * Out encoding: Currently ignored. * After-connection IRC command: A
raw IRC command that will be sent to the server immediately after the connection has been successful.
It can for example be used to identify yourself using NickServ, with a command like this: PRIVMSG
NickServ :identify PASSWORD. * Ports: The list of TCP ports to use when connecting to this IRC server.
This list will be tried in sequence, until the connection succeeds for one of them. The connection
made on these ports will not use TLS, the communication will be insecure. The default list contains
6697 and 6670. * TLS ports: A second list of ports to try when connecting to the IRC server. The only
difference is that TLS will be used if the connection is established on one of these ports. All the
ports in this list will be tried before using the other plain-text ports list. To entirely disable any
non-TLS connection, just remove all the values from the “normal” ports list. The default list contains
6697. * Verify certificate: If set to true (the default value), when connecting on a TLS port, the
connection will be aborted if the certificate is not valid (for example if it's not signed by a known
authority, or if the domain name doesn't match, etc). Set it to false if you want to connect on a
server with a self-signed certificate. * SHA-1 fingerprint of the TLS certificate to trust: if you
know the hash of the certificate that the server is supposed to use, and you only want to accept this
one, set its SHA-1 hash in this field. * Server password: A password that will be sent just after the
connection, in a PASS command. This is usually used in private servers, where you're only allowed to
connect if you have the password. Note that, although this is NOT a password that will be sent to
NickServ (or some author authentication service), some server (notably Freenode) use it as if it was
sent to NickServ to identify your nickname.
• get-irc-connection-info: Returns some information about the IRC server, for the executing user. It
lets the user know if they are connected to this server, from what port, with or without TLS, and it
gives the list of joined IRC channel, with a detailed list of which resource is in which channel.
On a channel JID (e.g on the JID
#test%chat.<freenode.org@biboumi.example.com>)
• configure: Lets each user configure some options that applies to the concerned IRC channel. Some of
these options, if not configured for a specific channel, defaults to the value configured at the IRC
server level. For example the encoding can be specified for both the channel and the server. If an
encoding is not specified for a channel, the encoding configured in the server applies. The provided
configuration form contains these fields: * In encoding: see the option with the same name in the
server configuration form. * Out encoding: Currently ignored. * Persistent: If set to true, biboumi
will stay in this channel even when all the XMPP resources have left the room. I.e. it will not send
a PART command, and will stay idle in the channel until the connection is forcibly closed. If a
resource comes back in the room again, and if the archiving of messages is enabled for this room, the
client will receive the messages that where sent in this channel. This option can be used to make
biboumi act as an IRC bouncer. * Record History: whether or not history messages should be saved in
the database, for this specific channel. If the value is “unset” (the default), then the value
configured globally is used. This option is there, for example, to be able to enable history recording
globally while disabling it for a few specific “private” channels.
Raw IRC messages
Biboumi tries to support as many IRC features as possible, but doesn't handle everything yet (or ever).
In order to let the user send any arbitrary IRC message, biboumi forwards any XMPP message received on an
IRC Server JID (see Addressing ()) as a raw command to that IRC server.
For example, to WHOIS the user Foo on the server irc.example.com, a user can send the message “WHOIS Foo”
to irc.example.com@biboumi.example.com.
The message will be forwarded as is, without any modification appart from adding \r\n at the end (to make
it a valid IRC message). You need to have a little bit of understanding of the IRC protocol to use this
feature.
Security
The connection to the XMPP server can only be made on localhost. The XMPP server is not supposed to
accept non-local connections from components. Thus, encryption is not used to connect to the local
XMPP server because it is useless.
If compiled with the Botan library, biboumi can use TLS when communicating with the IRC servers. It will
first try ports 6697 and 6670 and use TLS if it succeeds, if connection fails on both these ports, the
connection is established on port 6667 without any encryption.
Biboumi does not check if the received JIDs are properly formatted using nodeprep. This must be done by
the XMPP server to which biboumi is directly connected.
Note if you use a biboumi that you have no control on: remember that the administrator of the gateway you
use is able to view all your IRC conversations, whether you're using encryption or not. This is exactly
as if you were running your IRC client on someone else's server. Only use biboumi if you trust its
administrator (or, better, if you are the administrator) or if you don't intend to have any private
conversation.
Biboumi does not provide a way to ban users from connecting to it, has no protection against flood or any
sort of abuse that your users may cause on the IRC servers. Some XMPP server however offer the
possibility to restrict what JID can access a gateway. Use that feature if you wish to grant access to
your biboumi instance only to a list of trusted users.