1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
|
```
Filename: 119-controlport-auth.txt
Title: New PROTOCOLINFO command for controllers
Author: Roger Dingledine
Created: 14-Aug-2007
Status: Closed
Implemented-In: 0.2.0.x
Overview:
Here we describe how to help controllers locate the cookie
authentication file when authenticating to Tor, so we can a) require
authentication by default for Tor controllers and b) still keep
things usable. Also, we propose an extensible, general-purpose mechanism
for controllers to learn about a Tor instance's protocol and
authentication requirements before authenticating.
The Problem:
When we first added the controller protocol, we wanted to make it
easy for people to play with it, so by default we didn't require any
authentication from controller programs. We allowed requests only from
localhost as a stopgap measure for security.
Due to an increasing number of vulnerabilities based on this approach,
it's time to add authentication in default configurations.
We have a number of goals:
- We want the default Vidalia bundles to transparently work. That
means we don't want the users to have to type in or know a password.
- We want to allow multiple controller applications to connect to the
control port. So if Vidalia is launching Tor, it can't just keep the
secrets to itself.
Right now there are three authentication approaches supported
by the control protocol: NULL, CookieAuthentication, and
HashedControlPassword. See Sec 5.1 in control-spec.txt for details.
There are a couple of challenges here. The first is: if the controller
launches Tor, how should we teach Tor what authentication approach
it should require, and the secret that goes along with it? Next is:
how should this work when the controller attaches to an existing Tor,
rather than launching Tor itself?
Cookie authentication seems most amenable to letting multiple controller
applications interact with Tor. But that brings in yet another question:
how does the controller guess where to look for the cookie file,
without first knowing what DataDirectory Tor is using?
Design:
We should add a new controller command PROTOCOLINFO that can be sent
as a valid first command (the others being AUTHENTICATE and QUIT). If
PROTOCOLINFO is sent as the first command, the second command must be
either a successful AUTHENTICATE or a QUIT.
If the initial command sequence is not valid, Tor closes the connection.
Spec:
C: "PROTOCOLINFO" *(SP PIVERSION) CRLF
S: "250+PROTOCOLINFO" SP PIVERSION CRLF *InfoLine "250 OK" CRLF
InfoLine = AuthLine / VersionLine / OtherLine
AuthLine = "250-AUTH" SP "METHODS=" AuthMethod *(",")AuthMethod
*(SP "COOKIEFILE=" AuthCookieFile) CRLF
VersionLine = "250-VERSION" SP "Tor=" TorVersion [SP Arguments] CRLF
AuthMethod =
"NULL" / ; No authentication is required
"HASHEDPASSWORD" / ; A controller must supply the original password
"COOKIE" / ; A controller must supply the contents of a cookie
AuthCookieFile = QuotedString
TorVersion = QuotedString
OtherLine = "250-" Keyword [SP Arguments] CRLF
For example:
C: PROTOCOLINFO CRLF
S: "250+PROTOCOLINFO 1" CRLF
S: "250-AUTH Methods=HASHEDPASSWORD,COOKIE COOKIEFILE="/tor/cookie"" CRLF
S: "250-VERSION Tor=0.2.0.5-alpha" CRLF
S: "250 OK" CRLF
Tor MAY give its InfoLines in any order; controllers MUST ignore InfoLines
with keywords it does not recognize. Controllers MUST ignore extraneous
data on any InfoLine.
PIVERSION is there in case we drastically change the syntax one day. For
now it should always be "1", for the controller protocol. Controllers MAY
provide a list of the protocol versions they support; Tor MAY select a
version that the controller does not support.
Right now only two "topics" (AUTH and VERSION) are included, but more
may be included in the future. Controllers must accept lines with
unexpected topics.
AuthCookieFile = QuotedString
AuthMethod is used to specify one or more control authentication
methods that Tor currently accepts.
AuthCookieFile specifies the absolute path and filename of the
authentication cookie that Tor is expecting and is provided iff
the METHODS field contains the method "COOKIE". Controllers MUST handle
escape sequences inside this string.
The VERSION line contains the Tor version.
[What else might we want to include that could be useful? -RD]
Compatibility:
Tor 0.1.2.16 and 0.2.0.4-alpha hang up after the first failed
command. Earlier Tors don't know about this command but don't hang
up. That means controllers will need a mechanism for distinguishing
whether they're talking to a Tor that speaks PROTOCOLINFO or not.
I suggest that the controllers attempt a PROTOCOLINFO. Then:
- If it works, great. Authenticate as required.
- If they get hung up on, reconnect and do a NULL AUTHENTICATE.
- If it's unrecognized but they're not hung up on, do a NULL
AUTHENTICATE.
Unsolved problems:
If Torbutton wants to be a Tor controller one day... talking TCP is
bad enough, but reading from the filesystem is even harder. Is there
a way to let simple programs work with the controller port without
needing all the auth infrastructure?
Once we put this approach in place, the next vulnerability we see will
involve an attacker somehow getting read access to the victim's files
--- and then we're back where we started. This means we still need
to think about how to demand password-based authentication without
bothering the user about it.
```
|
