[or-cvs] r15655: Proposal 121: Add a simple algorithm to delay descriptor pub (tor/trunk/doc/spec/proposals)
kloesing at seul.org
kloesing at seul.org
Fri Jul 4 15:39:21 UTC 2008
Author: kloesing
Date: 2008-07-04 11:39:21 -0400 (Fri, 04 Jul 2008)
New Revision: 15655
Modified:
tor/trunk/doc/spec/proposals/121-hidden-service-authentication.txt
tor/trunk/doc/spec/proposals/142-combine-intro-and-rend-points.txt
Log:
Proposal 121: Add a simple algorithm to delay descriptor publication for different clients of a hidden service;
Proposal 142: Give first security property the new name "Responsibility" and change new cell formats according to rendezvous protocol version 3 draft.
Modified: tor/trunk/doc/spec/proposals/121-hidden-service-authentication.txt
===================================================================
--- tor/trunk/doc/spec/proposals/121-hidden-service-authentication.txt 2008-07-04 14:44:43 UTC (rev 15654)
+++ tor/trunk/doc/spec/proposals/121-hidden-service-authentication.txt 2008-07-04 15:39:21 UTC (rev 15655)
@@ -16,6 +16,8 @@
24-Dec-2007 Replaced misleading term "authentication" by "authorization"
and added some clarifications (comments by Sven Kaffille)
28-Apr-2008 Updated most parts of the concrete authorization protocol
+ 04-Jul-2008 Add a simple algorithm to delay descriptor publication for
+ different clients of a hidden service
Overview:
@@ -176,6 +178,20 @@
cookie per group of users. It is up to the specific protocol and how it
is applied by a service provider.
+ Two or more hidden service descriptors for different groups or users
+ should not be uploaded at the same time. A directory node could conclude
+ easily that the descriptors, were issued by the same hidden service, thus
+ being able to link the two groups or users. Therefore, descriptors for
+ different users or clients that ought to be stored on the same directory
+ are delayed, so that only one descriptor is uploaded to a directory at a
+ time. The remaining descriptors are uploaded with a delay of 30 seconds.
+ Further, descriptors for different groups or users that are to be stored
+ on different directories are delayed for a random time of up to 30
+ seconds to hide relations from colluding directories. Certainly, this
+ does not prevent linking entirely, but it makes it somewhat harder.
+ There is a conflict between hiding links between clients and making a
+ service available in a timely manner.
+
Although this part of the proposal is meant to describe a general
infrastructure for authorization, changing the way of using the
descriptor cookie to look up hidden service descriptors, e.g. applying
@@ -360,8 +376,8 @@
services maintain a history of received INTRODUCE2 cells within the last
hour and only accept INTRODUCE2 cells matching the following rules:
- (1) a maximum of 3 cells coming from the same client and containing the
- same rendezvous cookie, and
+ (1) no duplicate requests coming from the same client and containing
+ the same rendezvous cookie, and
(2) a maximum of 10 cells coming from the same client with different
rendezvous cookies.
@@ -467,7 +483,7 @@
in INTRODUCE2 cells that it sends to the server.
The server compares authorization data of incoming INTRODUCE2 cells with
the locally stored value that it would expect. The authorization type
- number of this protocol for INTRODUCE2 cells is "1".
+ number of this protocol for INTRODUCE2 cells is "2".
2.4. Providing authorization data
@@ -483,6 +499,7 @@
or generated and appended to that file. The file format is:
"client-name" human-readable client identifier NL
+ "service-address" onion-address NL
"descriptor-cookie" 128-bit key ^= 22 base64 chars NL
"client-key" NL a public key in PEM format
Modified: tor/trunk/doc/spec/proposals/142-combine-intro-and-rend-points.txt
===================================================================
--- tor/trunk/doc/spec/proposals/142-combine-intro-and-rend-points.txt 2008-07-04 14:44:43 UTC (rev 15654)
+++ tor/trunk/doc/spec/proposals/142-combine-intro-and-rend-points.txt 2008-07-04 15:39:21 UTC (rev 15655)
@@ -9,6 +9,9 @@
Change history:
27-Jun-2008 Initial proposal for or-dev
+ 04-Jul-2008 Give first security property the new name "Responsibility"
+ and change new cell formats according to rendezvous protocol
+ version 3 draft.
Overview:
@@ -22,7 +25,7 @@
service.
There are some reasons for separating the two roles of introduction and
- rendezvous point: (1) Plausible deniability: A relay shall not be made
+ rendezvous point: (1) Responsibility: A relay shall not be made
responsible that it relays data for a certain hidden service; in the
original design as described in [1] an introduction point relays no
application data, and a rendezvous points neither knows the hidden
@@ -44,8 +47,8 @@
introduced new introduction keys for introduction points and provides for
user authorization data in hidden service descriptors; it will be shown
in this proposal that introduction keys in combination with new
- introduction cookies provide for the first security property of plausible
- deniability. Further, eliminating the need for a separate introduction
+ introduction cookies provide for the first security property
+ responsibility. Further, eliminating the need for a separate introduction
connection benefits the overall network load by decreasing the number of
circuit extensions. After all, having only one connection between client
and hidden service reduces the overall protocol complexity.
@@ -69,17 +72,15 @@
version that implements this proposal.
The easiest way to implement establishment of contact points is to
- introduce v2 ESTABLISH_INTRO cells and use the currently unused auth type
- number 1 for contact points.
+ introduce v2 ESTABLISH_INTRO cells. By convention, the relay recognizes
+ version 2 ESTABLISH_INTRO cells as requests to establish a contact point
+ rather than an introduction point.
V Format byte: set to 255 [1 octet]
V Version byte: set to 2 [1 octet]
KLEN Key length [2 octets]
- PK Bob's public key [KLEN octets]
+ PK Public introduction key [KLEN octets]
HS Hash of session info [20 octets]
- AUTHT The auth type that is supported [1 octet]
- AUTHL Length of auth data [2 octets]
- AUTHD Auth data [variable]
SIG Signature of above information [variable]
The hidden service does not create a fixed number of contact points, like
@@ -98,16 +99,17 @@
established introduction point. By requiring clients to use this cookie
in a later connection establishment, an introduction point cannot access
the hidden service that it works for. Together with the fresh
- introduction key that was introduced in proposal 114, this results in
- plausible deniability for the contact point.
+ introduction key that was introduced in proposal 114, this reduces
+ responsibility of a contact point for a specific hidden service.
The v2 hidden service descriptor format contains an
"intro-authentication" field that may contain introduction-point specific
keys. The hidden service creates a random string, comparable to the
rendezvous cookie, and includes it in the descriptor as introduction
- cookie. Existing clients that do not understand this new protocol simply
- ignore that cookie. Further, the hidden service lists in the
- "protocol-versions" field that it supports this protocol.
+ cookie for auth-type "1". By convention, clients recognize existence of
+ auth-type 1 as possibility to connect to a hidden service via a contact
+ point rather than an introduction point. Older clients that do not
+ understand this new protocol simply ignore that cookie.
4. Connection Establishment
@@ -128,30 +130,22 @@
Cleartext
V Version byte: set to 2 [1 octet]
PK_ID Identifier for Bob's PK [20 octets]
- AUTHT The auth type that is supported [1 octet]
- AUTHL Length of auth data [2 octets]
- AUTHD Auth data [variable]
- Encrypted to Bob's PK:
+ RC Rendezvous cookie [20 octets]
+ Encrypted to introduction key:
VER Version byte: set to 3. [1 octet]
AUTHT The auth type that is supported [1 octet]
AUTHL Length of auth data [2 octets]
AUTHD Auth data [variable]
- IP Rendezvous point's address [4 octets]
- PORT Rendezvous point's OR port [2 octets]
- ID Rendezvous point identity ID [20 octets]
- KLEN Length of onion key [2 octets]
- KEY Rendezvous point onion key [KLEN octets]
RC Rendezvous cookie [20 octets]
g^x Diffie-Hellman data, part 1 [128 octets]
- The cleartext part contains the rendezvous cookie as auth data for the
- currently unused auth type 1. The contact point remembers the rendezvous
- cookie just as a rendezvous point would do.
+ The cleartext part contains the rendezvous cookie that the contact point
+ remembers just as a rendezvous point would do.
The encrypted part contains the introduction cookie as auth data for the
- likewise unused auth type 1. The rendezvous cookie is contained as
- before, but the remaining rendezvous point information is left empty, as
- there is no separate rendezvous point.
+ auth type 1. The rendezvous cookie is contained as before, but there is
+ no further rendezvous point information, as there is no separate
+ rendezvous point.
5. Rendezvous Establishment
@@ -177,7 +171,7 @@
Security Implications:
- (1) Plausible deniability
+ (1) Responsibility
One of the original reasons for the separation of introduction and
rendezvous points is that a relay shall not be made responsible that it
@@ -191,11 +185,10 @@
cookie, which is unknown to the contact point, prevents it from accessing
the hidden service itself. The only way for a contact point to access a
hidden service is to look up whether it is contained in the descriptors
- of known hidden services. A contact point can plausibly deny knowledge of
- any hidden services, so that it cannot know for which hidden service it
- is working. In addition to that, it cannot learn the data that it
- transfers, because all communication between client and hidden service
- are end-to-end encrypted.
+ of known hidden services. A contact point cannot directly be made
+ responsible for which hidden service it is working. In addition to that,
+ it cannot learn the data that it transfers, because all communication
+ between client and hidden service are end-to-end encrypted.
(2) Scalability
@@ -205,7 +198,7 @@
better scalability.
The new protocol eliminates the need for a hidden service to extend
- circuits on demand, which has a positive effect circuits establishment
+ circuits on demand, which has a positive effect on circuits establishment
times and overall network load. The solution presented here to establish
a number of contact points proportional to the history of connection
requests reduces the number of circuits to a minimum number that fits the
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