The purpose of this is to enable remote and unattended rebooting of client host computer with an encrypted root file system. See the section called "OVERVIEW" for details.
--interface NAME, -i NAME
--address ADDRESS, -a ADDRESS
--port PORT, -p PORT
This is part of the Mandos system for allowing computers to have encrypted root file systems and at the same time be capable of remote and/or unattended reboots. The computers run a small client program in the initial RAM disk environment which will communicate with a server over a network. All network communication is encrypted using TLS. The clients are identified by the server using an OpenPGP key; each client has one unique to it. The server sends the clients an encrypted password. The encrypted password is decrypted by the clients using the same OpenPGP key, and the password is then used to unlock the root file system, whereupon the computers can continue booting normally.
This program is the server part. It is a normal server program and will run in a normal system environment, not in an initial RAM disk environment.
The Mandos server announces itself as a Zeroconf service of type "_mandos._tcp". The Mandos client connects to the announced address and port, and sends a line of text where the first whitespace-separated field is the protocol version, which currently is "1". The client and server then start a TLS protocol handshake with a slight quirk: the Mandos server program acts as a TLS "client" while the connecting Mandos client acts as a TLS "server". The Mandos client must supply an OpenPGP certificate, and the fingerprint of this certificate is used by the Mandos server to look up (in a list read from clients.conf at start time) which binary blob to give the client. No other authentication or authorization is done by the server.
Table 1. Mandos Protocol (Version 1)
TLS handshake as TLS "server"
TLS handshake as TLS "client"
|OpenPGP public key (part of TLS handshake)||->||
Binary blob (client will assume OpenPGP data)
The server will, by default, continually check that the clients are still up. If a client has not been confirmed as being up for some time, the client is assumed to be compromised and is no longer eligible to receive the encrypted password. (Manual intervention is required to re-enable a client.) The timeout, checker program, and interval between checks can be configured both globally and per client; see mandos-clients.conf(5). A client successfully receiving its password will also be treated as a successful checker run.
The server will send log message with various severity levels to /dev/log. With the --debug option, it will log even more messages, and also show them on the console.
The server will exit with a non-zero exit status only when a critical error is encountered.
Use the --configdir option to change where mandos looks for its configurations files. The default file names are listed here.
This server might, on especially fatal errors, emit a Python backtrace. This could be considered a feature.
Currently, if a client is declared "invalid" due to having timed out, the server does not record this fact onto permanent storage. This has some security implications, see the section called "CLIENTS".
There is currently no way of querying the server of the current status of clients, other than analyzing its syslog output.
There is no fine-grained control over logging and debug output.
Debug mode is conflated with running in the foreground.
The console log messages do not show a time stamp.
This server does not check the expire time of clients' OpenPGP keys.
Normal invocation needs no options:
Run the server in debug mode, read configuration files from the ~/mandos directory, and use the Zeroconf service name "Test" to not collide with any other official Mandos server on this host:
mandos --debug --configdir ~/mandos --servicename Test
Run the server normally, but only listen to one interface and only on the link-local address on that interface:
mandos --interface eth7 --address fe80::aede:48ff:fe71:f6f2
Running this mandos server program should not in itself present any security risk to the host computer running it. The program switches to a non-root user soon after startup.
The server only gives out its stored data to clients which does have the OpenPGP key of the stored fingerprint. This is guaranteed by the fact that the client sends its OpenPGP public key in the TLS handshake; this ensures it to be genuine. The server computes the fingerprint of the key itself and looks up the fingerprint in its list of clients. The clients.conf file (see mandos-clients.conf(5)) must be made non-readable by anyone except the user starting the server (usually root).
As detailed in the section called "CHECKING", the status of all client computers will continually be checked and be assumed compromised if they are gone for too long.
If a client is compromised, its downtime should be duly noted by the server which would therefore declare the client invalid. But if the server was ever restarted, it would re-read its client list from its configuration file and again regard all clients therein as valid, and hence eligible to receive their passwords. Therefore, be careful when restarting servers if it is suspected that a client has, in fact, been compromised by parties who may now be running a fake Mandos client with the keys from the non-encrypted initial RAM image of the client host. What should be done in that case (if restarting the server program really is necessary) is to stop the server program, edit the configuration file to omit any suspect clients, and restart the server program.
For more details on client-side security, see mandos-client(8mandos).
mandos-clients.conf(5), mandos.conf(5), mandos-client(8mandos), sh(1)
RFC 4291: IP Version 6 Addressing Architecture
Section 2.2: Text Representation of Addresses
Section 188.8.131.52: IPv4-Mapped IPv6 Address
Section 2.5.6, Link-Local IPv6 Unicast Addresses
RFC 4346: The Transport Layer Security (TLS) Protocol Version 1.1
RFC 4880: OpenPGP Message Format
RFC 5081: Using OpenPGP Keys for Transport Layer Security
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