module Rpc_auth_dh:sig
..end
This module implements DH authentication, the simplest form of Secure RPC. Despite its name, this form of authentication provides only a medium level of security, see below.
To use AUTH_DH you need the public-key infrastructure for Secure
RPC. This requires that a special daemon, the so-called keyserv
,
runs on both the client's system and the server's system. The task
of keyserv
is to store public and private keys. We do not have
a keyserv
in Ocamlnet, so you must use the keyserv
your system
provides.
(Note that keyserv
is often distributed together with NIS+. However,
you can run keyserv
without needing to set up NIS+.)
In order to make a remote call, the keyserv daemon
of the client must
know the private key of the client user, and the public key of the
server user. The keyserv
daemon of the server must know the public
key of the client user and the private key of the server user.
Note that you can load a key pair into keyserv
with the command keylogin
.
(This is not necessary for the root user, root's key pair is loaded
at daemon startup time.)
See the manual pages of your OS
for keyserv
, keylogin
, keylogout
, and /etc/publickey
.
Furthermore, it is strictly necessary that time synchronization is enabled between the client and the server. The recommended solution is to synchronize both clocks independently using a time normal (with NTP). Alternatively, the server can provide a time service on port 37 ("netdate").
To identify users, AUTH_DH uses so-called netnames. These have the form "<osflavor>.<user>@<domain>", where <osflavor> determines the kind of operating system (usually "unix"), <user> is an identifier for the user, and <domain> determines where the user identifiers are valid. In UNIX environments, the netnames are formed like:
keyserv
daemon provides a service net_get
that returns the netname of
the calling user. AUTH_DH uses this service to determine the netname
of the current process, but this does not hide netnames from the user
of AUTH_DH:
Note that it is hard to attack AUTH_DH without knowing the public key.
So it is best not to make it accessible for third parties.
val domainname : unit -> string
domainname
.
Note: This function refuses to work for setuid or setgid programs.val client_auth_method : ?ttl:int ->
?getdeviation:(Unix.inet_addr -> float) ->
?key_lifetime:int ->
?keyserv:Rpc_key_service.connector -> string -> Rpc_client.auth_method
Pass the resulting auth_method to Rpc_client.set_auth_methods
to
configure AUTH_DH for an RPC client.
ttl
: The "time to live" for the network packets. Effectively, this
number is the maximum time deviation the server will tolerate. It
defaults to 60 seconds meaning that it is acceptable if the server
gets the network packet 60/2 seconds before or after the time the packet
is sent by the client.getdeviation
: This function is called when the time has to be
resynchronized. The argument is the internet address of the server,
and the expected result is the number of seconds the server is ahead
to the client.
By default, a function is used that connects to the netdate time
service of the server, and compares the time of the client and the
server.
If the clocks can be assumed to always be synchronous, it is safe to
pass fun _ -> 0.0
as deviation function.key_lifetime
: After this number of seconds the DES key (conversation
key) expires. Default: 3600val server_auth_method : ?max_sessions:int ->
?max_ttl:int ->
?key_lifetime:int ->
?attack_detector:bool ->
?keyserv:Rpc_key_service.connector -> unit -> Rpc_server.auth_method
Rpc_server.set_auth_methods
to
configure AUTH_DH for an RPC server.
Note that the current implementation of AUTH_DH blocks until the
keyserv
responds. For most applications, this is not a big problem,
as keyserv
lookups are seldom. Perhaps I will rewrite the code some
day such that keyserv
lookups are done in an asynchronous way. (The
Rpc_server.auth_method
interface allows it already.)
max_sessions
: The maximum number of authenticated connections the
server can manage. If more clients connect, the lifetime of the
conversation keys will decrease, but the server will still be
functional.max_ttl
: The maximum number for the ttl value. The ttl value is
passed by the client, but if it is bigger than max_ttl
, the maximum
is used instead.key_lifetime
: After this number of seconds the conversation key expires
and must be renewed.attack_detector
: Whether an attack detector is to be installed. It
detects if there are many failed connection attempts for a certain
user (more than 10 failures in 10 seconds). If this criterion matches
no more logins are allowed for this user in the current 10 seconds
period.
The detector contains a heuristics that makes it unlikely that
a TCP connection breaks when just a key must be renewed and the server
is currently being attacked.