P2PSIP Working Group H. Song
Internet-Draft Huawei
Intended status: Informational M. Matuszewski
Expires: May 7, 2009 Nokia
D. York
Voxeo
November 3, 2008
Security requirements in Peer-to-Peer Session Initiation Protocol
(P2PSIP)
draft-matuszewski-p2psip-security-requirements-04
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Abstract
This document outlines the security requirements for a Peer-to-Peer
Session Initiation Protocol (P2PSIP) overlay network. It compares
security difference between client/server (C/S) and P2P
implementations of SIP, partitions the P2PSIP architecture into
layers and analyzes the security issues in each layer and the
security relationship among the layers. This draft also describes
the different security requirements related to different application
scenarios as well as a minimal set of security requirements valid for
all applications. It also discusses open issues related to certain
security threats for the P2PSIP architecture and its components.
Table of Contents
1. Authors' Notes . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. P2PSIP network entity . . . . . . . . . . . . . . . . . . 6
3.3. P2PSIP system . . . . . . . . . . . . . . . . . . . . . . 6
3.4. P2P Overlay Base . . . . . . . . . . . . . . . . . . . . . 6
4. Security Comparison between C/S and P2P . . . . . . . . . . . 7
5. Security Analysis with P2P Layers . . . . . . . . . . . . . . 9
5.1. Transport Layer Security . . . . . . . . . . . . . . . . . 10
5.2. Routing Maintenance and KBR layer Security . . . . . . . . 10
5.3. Distributed Storage and Replication Layer Security . . . . 11
5.4. Application Layer Security . . . . . . . . . . . . . . . . 12
6. Security Analysis with Application Scenarios . . . . . . . . . 13
6.1. Trusted P2P Overlay Base . . . . . . . . . . . . . . . . . 13
6.2. Untrusted P2P Overlay Base . . . . . . . . . . . . . . . . 15
7. Security requirements . . . . . . . . . . . . . . . . . . . . 18
7.1. User requirements . . . . . . . . . . . . . . . . . . . . 18
7.2. System requirements . . . . . . . . . . . . . . . . . . . 18
7.2.1. Dependence of reachability of a centralized server . . 18
7.2.2. Scalability . . . . . . . . . . . . . . . . . . . . . 18
7.2.3. Preference of existing security mechanisms . . . . . . 19
7.2.4. Requirements on a base P2P algorithm . . . . . . . . . 19
7.2.5. Node and user identification . . . . . . . . . . . . . 19
7.2.6. Enrollment . . . . . . . . . . . . . . . . . . . . . . 19
7.2.7. Replay attacks . . . . . . . . . . . . . . . . . . . . 20
7.2.8. Data access . . . . . . . . . . . . . . . . . . . . . 20
7.2.9. Data validation . . . . . . . . . . . . . . . . . . . 20
7.2.10. Denial of Service (DOS) attacks . . . . . . . . . . . 21
7.2.11. Privacy . . . . . . . . . . . . . . . . . . . . . . . 21
7.2.12. Detection and rejection of badly behaving nodes . . . 21
7.2.13. Summary of the system requirements . . . . . . . . . . 22
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8. Security Considerations . . . . . . . . . . . . . . . . . . . 24
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26
11. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
11.1. Revision 4 . . . . . . . . . . . . . . . . . . . . . . . . 27
12. Appendix: Security threats . . . . . . . . . . . . . . . . . . 28
12.1. Replay Attacks . . . . . . . . . . . . . . . . . . . . . . 28
12.2. Message Insertion, Modification, Deletion . . . . . . . . 28
12.3. Man-In-The-Middle . . . . . . . . . . . . . . . . . . . . 30
12.4. Offline Cryptographic Attacks . . . . . . . . . . . . . . 30
12.5. Unauthorized Usage . . . . . . . . . . . . . . . . . . . . 31
12.6. Inappropriate Usage . . . . . . . . . . . . . . . . . . . 31
12.7. Denial of Service . . . . . . . . . . . . . . . . . . . . 32
12.8. Communication security threats . . . . . . . . . . . . . . 32
13. Normative References . . . . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
Intellectual Property and Copyright Statements . . . . . . . . . . 36
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1. Authors' Notes
This document represents a merge of two drafts:
o draft-matuszewski-p2psip-security-requirements
o [I-D.song-p2psip-security-eval]
with some post-merge editing by Song Haiban, Dan York and Marcin
Matuszewski. It is submitted to continue the ongoing dialogue within
the P2PSIP Working Group around security with the recognition that
further work needs to be done to complete the merger of the two
documents. The authors intend to do the following:
o The document will be synchronized with the recently released
updates to the RELOAD protocol as documented by editor Bruce
Lowekamp in [I-D.ietf-p2psip-sip] and [I-D.ietf-p2psip-base]
o The merge between the two previous documents will be completed so
that the text flows better.
o A section will be added on security requirements related to
interconnection of P2PSIP networks to other networks including
non-P2P SIP networks and the PSTN.
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2. Introduction
The scope of this document is to analyze security threats concerning
a P2PSIP overlay architecture as described in the concepts and
terminology for P2PSIP document [1] and list security requirements
for the architecture and its components. It compares security
difference between client/server (C/S) and P2P implementations of
SIP, partitions the P2PSIP architecture into layers and analyzes the
security issues in each layer and the security relationship among the
layers. This draft also classifies the application scenarios into
two main types and then analyzes in detail the security threats with
these two types of scenarios. In the end, it summarizes the main
security requirements for the P2PSIP architecture and its components.
An appendix presents an introduction to security threats to P2PSIP
environments.
This document is intended to list the security requirements that must
be addressed in P2PSIP specifications. Some solutions to certain
attacks are given as an example in the analysis text. This document
is a merge of features from the security requirement draft version
and the security analysis and evaluation draft
[I-D.song-p2psip-security-eval]. It complements the P2PSIP Protocol
Framework and Requirements document [I-D.bryan-p2psip-requirements].
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3. Definitions
This section defines a number of concepts that are key to understand
the rest of the document.
3.1. General
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3.2. P2PSIP network entity
A P2PSIP network entity is a peer, client, or other functional node
that may become a part of a P2PSIP overlay.
3.3. P2PSIP system
A P2PSIP system consists of the P2PSIP overlay as defined in [1] and
one or more enrollment servers. The enrollment servers issue unique
identities and credentials that are used to authenticate and admit
P2PSIP network entities to the overlay and allow a user to use
services provided by the P2PSIP overlay. The enrollment server may
also provide an initial set of bootstrap nodes.
3.4. P2P Overlay Base
P2P Overlay Base: A P2P Overlay Base includes all the Peers that
participate in the p2p overlay. The P2P Overlay Base provides
distributed storage and routing services to both peers and
clients.
Trusted P2P Overlay Base: All peers in a Trusted P2P Overlay Base are
trusted. The Peers in the overlay are all of good behaviors and
under control due to deployment. For example, a carrier deploys
a Trusted P2P Overlay Base to provide service to his customers,
and all the peers are the carrier's devices.
Untrusted P2P Overlay Base: Peers in a Untrusted P2P Overlay Base
are not all trusted. There may exist some malicious behaving
nodes in the P2P Overlay Base.
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4. Security Comparison between C/S and P2P
In a Client Server(C/S) architecture, a client asks for a specific
service only from a specific server. The destination contact
address(i.e. the address of that server) can be acquired from the
trusted DNS system directly. Given this, the security issues exist
only with the connection between the client and the server.
Typically, making the connection secure between the client and the
server addresses most of the security issues related to the client.
However, in a P2P architecture the security issues are more complex.
First, where in a C/S architecture specific servers provide certain
services, in a P2P architecture, each peer in the P2P overlay can
provide distributed storage and transport services for other P2P
entities. There is also no hierarchy of servers but instead the
peers self-organize into the P2P overlay.
Second, where in a C/S architecture a client sends its request
directly to a server, in a P2P architecture a peer sends messages
through Key-Based-Routing and it doesn't know where the destination
is. There exist intermediate nodes between the source and
destination.
Third, where in a C/S architecture the client can trust the
information from the server, in a P2P architecture, one peer does not
know whether it should trust the information acquired from the
overlay.
So in a P2P architecture, security issues not only exist between end
to end entities, but also between hop by hop services. They are not
only related to the routing security, but also related to the content
security.
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+------------+----------------------+--------------------------+
| | | |
| | C/S | P2P |
+------------+----------------------+--------------------------+
| | | |
| transport | authenticate between | authentication between |
| | client and server | P2PSIP network entities |
| | | |
+------------+----------------------+--------------------------+
| |need one hop security;| need hop by hop security|
| routing |transport layer | to ensure the end to end|
| |security can ensure it| security |
+------------+----------------------+--------------------------+
| | | responsible peer may not |
| storage | server is trusted for| trusted, need for resource|
| | storage | data management security |
+------------+----------------------+--------------------------+
| | | |
| application| out of scope of this| out of scope of this |
| | specification | specification |
| | | |
+------------+----------------------+--------------------------+
Figure 1 Comparision between C/S and P2P security
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5. Security Analysis with P2P Layers
The overall security of a P2PSIP system depends upon the security of
each layer of the P2PSIP architecture. In this section we split the
P2PSIP architecture into four main layers, as shown in the following
figure, and analyze the security issues from the P2PSIP architecture
perspective.
+----------+
| | Application Layer
| | --------------------------------------
| | +------+ +-------------+ +-------------+
| | | | | Distributed | | Replication |
| | | | | Storage | | |
| | | | +-------------+ +-------------+
| | | |--------------------------------------
|Enrollment| |P2P | +-------------+
|Server | |Layers| | Routing |
| | | | | Maintenance | +-----------+
| | | | +-------------+ | NAT&FW |
| | | | +-------------+ | Traversal |
| | | | | Key Based | +-----------+
| | | | | Routing(KBR)|
| | +------+ +-------------+
| | --------------------------------------
| | Transport Layer Security(TLS,DTLS)
+----------+
Figure 2 P2PSIP architecture
The four main layers are:
Transport Layer: Provides transport service for the upper layers.
Routing Maintenance and KBR Layer: Maintains the routing table, and
do the Key Based Routing(KBR). NAT and Firewall traversal may be
involved to establish direct connections.
Distributed Storage and Replication Layer: Stores and Manages the
resource objects. Each peer's responsible resource objects are
determined by the specific P2P algorithm. Replication may be
utilized to ensure the availability of resource objects under churn.
Application Layer: Provides the user application, and invokes the
services provided by the Distributed Storage and Replication Layer.
The security measures adopted in the lower layer may impact the upper
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layer security choices. Not every security threat needs to be
considered in each layer and typically each security threat only
needs to be solved in one of the layers. The question of in which
layer a specific security threat should be solved is addressed in our
primary analysis of each layer in the following sub-sections.
5.1. Transport Layer Security
Given that a P2PSIP overlay can run on top of the Internet or other
untrusted network, messages between associated nodes should be
protected against attacks(such as Man-in-the-Middle). In order to
establish the identity trust association, nodes SHOULD authenticate
each other with e.g. TLS and DTLS. If transport service security is
provided, we can prevent nodes without valid identities to
participate in the overlay. This layer must provides reliable and
secure hop-by-hop transport service for the P2P overlay. This alone,
though, is not enough to secure the P2P system.
5.2. Routing Maintenance and KBR layer Security
Each Peer in the P2PSIP overlay provides key-based routing service to
other peers and a routing maintenance mechanism is used to keep the
routing table timely and correct for the routing service. There are
some security threats with the routing table updating interaction and
the key-based routing.
Even if all the nodes participating in the P2PSIP overlay have valid
identities, the overlay may still be attacked by responding with fake
routing table to UPDATE requests. If the routing table is false, the
routing determination based on it will be false too. So,
verification mechanisms SHOULD be adopted to verify if the routing
table one learned from another is correct or not. A correct routing
table is important for hop by hop security.
Second, some attacker who is not responsible for the destination ID
may respond to some requests when he is in the intermediate routing
path(May respond with a fabricated resource object or just says that
the searched resource object doesn't exist). Should the source node
verify whether the response peer is responsible for the request?
When and how does the source peer do that? Whether the response peer
is responsible for the request is important for the end to end
security.
Third, some attackers may discard the messages when forwarding, or on
purpose forward the message to a wrong next hop. Should the overlay
need a method to detect the misbehaving forwardings?
Chosen-ID attack makes the above security issues much more worse.
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Fourth, some attacks may cause the overlay under high churn rate.
For example, some peers may frequently join and leave the overlay.
Overlay wastes much more traffic to update the routing table, and
transfer relative resource objects under churn. It can also make the
routing messages fail.
In this case, we need a method to control nodes to join the
overlay. The join control entity, which may be a bootstrap server
or enrollment server, or a bootstrap peer, makes records of peers'
historical behaviors in the overlay and their historical join
requests. When it receives the join request from a peer to join
the overlay, it checks the historical records as mentioned above
to determine whether this peer is permitted to join at this point.
It will deny the node to join the overlay when it determines the
peer is not permitted to join. For example, if a peer joins and
leaves too frequently, it will be denied to join the overlay as a
peer for a period of time and instead it will be allowed to join
the overlay as a client.
The first and fourth issue above is about routing maintenance
function security, and the remain two issues are about the KBR
function security.
5.3. Distributed Storage and Replication Layer Security
Distributed storage and replication layer provides distributed
storage service for the resource objects that located in one's
responsible resource ID range, and the replication service to keep
the availability of resource objects under churn. The security
issues in this layer are typically end to end, and about the content
and authority security.
First, We need to protect resource objects when needed against
unauthorized data operation such as obtainment, modification or
removing. A solution for authorization is needed.
Second, The P2PSIP overlay needs a method to prevent attackers from
publishing malicious information that will cause a DDOS attack. For
example, Peer A may publish a very popular resource record with the
contact address of Peer B without B's permission. That causes
unexpected lots of connections to B which will make Peer B down.
Using certificate can't solve this problem, a check mechanism for the
resource object is needed.
Third, overlays work well for a reasonable amount of resource
objects, but crash more or less when inserting millions of resource
objects per node. Spam attacks can make overlays go down. Open
issue: Should the spam attack be considered in the distributed
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storage layer? Or is it only the responsibility of the application
layer to handle this problem?
Replication security is to TODO.
5.4. Application Layer Security
Application layer security requirements are out of scope of this
specification.
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6. Security Analysis with Application Scenarios
As described in the security considerations section in the
application scenarios draft [I-D.bryan-p2psip-app-scenarios], the
security requirements of the various application scenarios vary
tremendously. So in this section, we divide the application
scenarios into two main types, instead of analyzing all the security
threats with each specific scenario described in the application
scenarios draft, we just analyze the relative security threats of
these two types, which represent most of the likely deployment
scenarios in the real world. For example, the "Public P2P VoIP
Service Providers" scenario in section 4.1.1 of application scenarios
draft may be deployed using the first type(refer to section 5.1 of
this specification), and the "Open Global P2P VoIP Network" scenario
in section 4.1.2 of application scenarios draft may be deployed using
the second type(refer to section 5.2 of this specification).
6.1. Trusted P2P Overlay Base
In a trusted P2P Overlay Base, all the peers are deployed with
trustful nodes. They are of good behaviors. They may deployed to
provide reliable and high quality services, and may also do some
management issues for the overlay. All P2PSIP clients access the
overlay service through the associated trusted peer. Shown as the
following figure 3.
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+---------+ +---------+
| Trusted +---------------+ Trusted |
| Peer | | Peer |
+---+-----+ +----+----+
| |
| |
|
| |
| P2PSIP Peer |
+---+-----+ Protocol +----+----+
| Trusted +---------------+ Trusted |
| Peer | | Peer |
+---+-----+ +----+----+
| |
P2PSIP Client |
Protocol |
+---+-----+ +----+----+
| | | |
|Client | | Client |
+---------+ +---------+
Figure 3 Trusted P2P Overlay Base
As for this type of scenarios, we regard the P2P Overlay Base to be
secure. The security issues to be considered are the transport
security between trusted peers and the security issues associated
with clients. Because clients doesn't provide routing service for
the overlay. Security issues more focus on distributed storage
layer. Some of the attacks are described in the appendix of this
draft.
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+--------------------+-----------------------+---------------------+
| Possible Attacks | Descriptions | Considerations |
|--------------------+-----------------------+---------------------+
| | 1.Message Privacy | TLS and DTLS |
| Transport Related | 2.ID hijack | |
+--------------------+-----------------------+---------------------+
|Unauthorized Data | Unauthorized Access, | Certificate |
|Operation | Modification, Removing| Mechanism |
+--------------------+-----------------------+---------------------+
| | In the progress of | |
| Man In the Middle | Authentication between| Authentication |
| | client and its | Security |
| | associated peer | |
+--------------------+-----------------------+---------------------+
| | | |
| data pollution and |1.Publish Fake Resource| 1.Check Mechanism? |
| poison | Objects | |
| |2.Publish malicious | 2.Black List? |
| | contact information | |
| | (DDOS attack) | |
+--------------------+-----------------------+---------------------+
| | | |
| Spam Attack | Publish lots of | 1. Check Mechanism? |
| | redundant resources | 2. Limit one's |
| | | publication number? |
+--------------------+-----------------------+---------------------+
Figure 4 Possible Attacks on the Trusted Overlay Base Scenarios
6.2. Untrusted P2P Overlay Base
In an untrusted P2P Overlay Base, there are peers who are not trusted
by other peers. Some of untrusted peers may do harmful things or
abnormal behaviors to the overlay due to malicious or unknown
intentions. There may or may not exist trusted peers in the overlay.
Shown as the following Figure 5.
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Please view in a fixed-width font such as
Courier.
+---------+ +---------+
|Untrusted+---------------+ Peer |
| Peer | | |
+---+-----+ +----+----+
| |
| |
| |
| |
| P2PSIP Peer |
+---+-----+ Protocol +----+----+
| Peer +---------------+Untrusted|
| | | Peer |
+---+-----+ +----+----+
| |
P2PSIP Client P2PSIP Client
Protocol Protocol
+---+-----+ +----+----+
| | | |
|Client | | Client |
+---------+ +---------+
Figure 5 Untrusted P2P Overlay Base
As for this type of scenarios, the security threats with the Trusted
P2P Overlay Base still exist, besides that, even more security issues
emerge, because there may exist malicious peers in this type of
scenarios. Each layer of the P2PSIP architecture and the enrollment
may be attacked, the attacks beyond those in the Trusted Overlay Base
scenarios are listed in the followings Figure 6.
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+--------------------+-----------------------+---------------------+
| Possible Attacks | Descriptions | Considerations |
|--------------------+-----------------------+---------------------+
| |1.Chosen-ID attack | 1.Enrollment Server |
| Identity Attack |2.Sybil Attack | |
| |3.Fabricated response | 2.A proof mechanism |
| | from the intermediate| to verify whether it|
| | peer | is a true root? |
+--------------------+-----------------------+---------------------+
| |1.discard messages | 1.message signature?|
| Forwarding Attack |2.Forwarding to a wrong| 2.A diagnosis |
| |next hop node | mechanism for |
| |3.modify messages when | detecting which |
| |forwarding | intermediate peer is|
| | | a bad man? |
+--------------------+-----------------------+---------------------+
| | Intermediate peer | |
| Replay Attack | stores messages and |Timestamp to |
| | replays |recognize timed |
| | |messages? |
+--------------------+-----------------------+---------------------+
| | give malicious | |
| Routing Table | response info to an |Per DHT specific? |
| Attack | updating routing table| |
| | request | |
+--------------------+-----------------------+---------------------+
Figure 6 Possible Attacks on the Untrusted Overlay Base Scenarios
As for these security issues, the diagnosis draft
[I-D.zheng-p2psip-diagnose] provides a framework using an ECHO
message to diagnose some of the problems in the P2PSIP overlay.
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7. Security requirements
This section describes requirements related to the security of a
P2PSIP system. We divided the requirements into user requirements
and system requirements.
7.1. User requirements
The user wants available and reliable service that enables him to
interact with other users and resources in a secure way. This means
that the P2PSIP system MUST provide:
o lookup and discovery of users and resources that is secure and
reliable,
o certainty of user and resource identity,
o confidentiality and integrity of end-to-end multimedia
communication,
o easy and secure enrollment to the P2PSIP system,
o privacy.
7.2. System requirements
In order for a P2PSIP system to function properly and that the end
user gets a proper service, there are several aspects that the P2PSIP
system must take in to account.
7.2.1. Dependence of reachability of a centralized server
Considering the nature of P2P in general, the dependence of
reachability of a centralized server SHOULD be minimized. There may
be unavoidable situations such as the enrollment process, where this
is not possible. However, the normal functioning of the P2PSIP
overlay such as join and leave operations, modification, retrieval
and deletion of P2PSIP resource (user) records from the P2PSIP system
should not depend on the reachability of a centralised server.
7.2.2. Scalability
P2PSIP security SHOULD scale from a small ad-hoc network to a network
with hundred millions of network nodes and users.
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7.2.3. Preference of existing security mechanisms
Although P2PSIP defines a new architecture, and thereby new
interfaces and protocols, for security there are several standardized
solutions for access control, authentication, integrity protection
and communication security. Using established protocols minimizes
potential security loopholes that need to be patched later. Besides
implementation is easer if chosen security protocols are widely
implemented and used.
7.2.4. Requirements on a base P2P algorithm
All of the security operations should be specified in such a way that
they do not impose new unnecessary requirements on a base P2P
algorithm (e.g., DHT implementations) and limit its scalability. The
security issues that are not introduced by the P2P algorithm MUST not
be isolated to the P2P algorithm to solve.
7.2.5. Node and user identification
The P2PSIP system MUST preserve user and resource identities. It
MUST NOT be possible to steal a P2PSIP identity from another user.
Because some attackers may try to use identities of another P2PSIP
network entities it must be possible to verify the identity of
another party.
7.2.6. Enrollment
The ease for users to enroll to a P2PSIP system SHOULD be ensured as
said in the section 4.1. The enrollment process defines the set of
users and P2PSIP network entities that may participate in a P2PSIP
system and issues them credentials. This process is defined by the
P2PSIP system, and the policy who can participate to is done during
this process. The enrollment process policy may define:
o how many and what user IDs and peer IDs an user or a P2PSIP
network entity may register,
o whether users are charged for the usage of the P2PSIP system,
o and how often they must re-new their subscription to the P2PSIP
system.
As it was indicated in [I-D.bryan-p2psip-requirements] the enrollment
process may take several measures in admitting a user or a network
node to the P2PSIP system, for example:
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o may require strong identity such as employment or identity
provided by a trusted 3rd party or by the P2PSIP service operator,
o may charge for the enrollment,
o may apply reputation mechanisms.
Although the user probably is the entity that enrolls to the P2PSIP
system, the credentials that are the result of the enrollment are
used to grant a device the right to function as a peer, client or any
other operative function possible in the system. Thus the security
of enrollment also translates to the security of the device itself
where the credentials are stored, and threats related to device
security in general.
7.2.7. Replay attacks
An attacker should not be able to repeat or delay valid data
transmission during enrollment and modification of P2PSIP resource
(user) records in a P2PSIP overlay.
7.2.8. Data access
An attacker MUST NOT be able to easily corrupt, delete, or overwrite
other user's or resource's data stored in P2PSIP resource (user)
records as well as routing tables. Only authorized users MUST be
able to modify, delete or overwrite their P2PSIP resource (user)
records in the P2PSIP system. P2PSIP security should allow users and
P2PSIP network entities to register the same resources (e.g.
TURN@overlay.net), however each entity should have rights only to its
own part of a resource record. In other words each entity should be
able to perform the same operations on its part of a resource record
as on its own resource (user) records.
The owner of the P2PSIP resource (user) records SHOULD be able to
authorize other users and network entities to modify, delete their
P2PSIP resource (user) records.
7.2.9. Data validation
First and foremost it MUST be possible to verify that the data stored
in or retrieved from the P2PSIP overlay is authentic, i.e. was not
tampered by unauthorized P2PSIP network entities.
The peer that stores P2PSIP resource (user) records MUST be able to
validate the data received in the process of P2PSIP resource (user)
record insertion and modification.
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7.2.10. Denial of Service (DOS) attacks
It MUST NOT be possible to obtain control of the location in the
overlay where the attacked user's or resource's records are
registered. In order to prevent so-called Sybil or join-leave
attacks the attacker SHOULD NOT be able to easily register a
unlimited number of IDs of his choice in the P2SIP overlay. The
P2PSIP system SHOULD be able to control ID assignment. Once
assigned, an ID or a set of IDs SHOULD be difficult to change.
In addition the P2PSIP architecture SHOULD make sure that data stored
in a P2PSIP overlay is persistent, meaning that even if a number of
nodes (but not all of nodes in the overlay) fails the data stored by
those nodes is not lost. In addition the attacker MUST NOT be able
to register unlimited number of resources in the overlay.
7.2.11. Privacy
The security of P2PSIP systems MUST guarantee privacy of the P2PSIP
network participants. The P2PSIP security SHOULD allow the users and
P2PSIP network entities to indicate which other users or P2PSIP
network entities can retrieve, modify, and delete data stored in
their P2PSIP resource (user) records. The owner of a P2PSIP resource
(user) record SHOULD be able to limit the access to his own resource
(user) records, and this feature should be enforced by the P2P
network.
It MUST also be difficult to monitor who is communicating with a
particular user, or retreive any contextual data about the user
without the user's explicit consent. The P2PSIP network entities
MUST be provided with option to encrypt data exchanged with other
P2PSIP network entities.
7.2.12. Detection and rejection of badly behaving nodes
It SHOULD be possible to limit potential damage caused by
malfunctioning and badly behaving nodes in a P2PSIP system. As the
policy taken by the P2PSIP system operator/community may be very
liberal, any user can obtain the right to be a user of a P2PSIP
system. It may be that some users behave badly intentionally in
which case it should be possible limit the impact of the badly
behaving nodes on the overall system security. It SHOULD be possible
to identify badly behaving nodes, and exclude or reject them from the
P2PSIP system.
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7.2.13. Summary of the system requirements
P2PSIP system requirements related to security issues are summarized
below:
Req. 1: Dependence of reachability of a centralized server SHOULD be
minimized.
Req. 2: P2PSIP security SHOULD scale from a small ad-hoc network to a
network with hundred millions of network nodes and users.
Req. 3: Existing security mechanisms SHOULD be used as much as
possible to protect P2PSIP functions, and avoid the need for
standardizing new mechanisms.
Req. 4: Security requirements on the base P2P algorithm (e.g., DHT
implementations) used in P2PSIP SHOULD be minimized and SHOULD NOT
limit its scalability.
Req. 5: The registered identities in a P2PSIP overlay MUST be
preserved. The attacker MUST NOT be able to steal identity from
another user.
Req. 6: The enrollment process MUST make it difficult for an attacker
to register many identities in a P2PSIP overlay and easily modify the
registered identities.
Req. 7: It MUST be difficult to select a particular peer ID e.g. peer
ID assignment process should introduce some degree of randomness to
peer identities.
Req. 8: It MUST be possible to authenticate users and P2PSIP network
entities.
Req. 9: It MUST NOT be possible to repeat or delay valid data
transmission during enrollment and modification of P2PSIP resource
(user) records.
Req. 10: The P2PSIP security MUST support integrity protection of the
data being inserted or retrieved to/from an overlay.
Req. 11: The P2PSIP network entities MUST be provided with an option
to encrypt data exchanged with other P2PSIP network entities.
Req. 12: Only authorized users and P2PSIP network entities MUST be
able to join the P2PSIP system and insert, modify, delete or
overwrite P2PSIP resource (user) records in the P2PSIP system.
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Req. 13: In the situations where many users or P2PSIP network
entities register the same resource in the P2PSIP overlay, each
entity MUST have rights only to its own part of a resource record.
Req. 14: An owner of P2PSIP resource (user) record MAY indicate which
users or network entities can retrieve, modify, and delete data
stored in their P2PSIP resource (user) records.
Req. 15: P2PSIP overlay protocols MUST be designed such a way so that
the effect of DOS attacks on the P2PSIP overlay is minimized.
Req. 16: It SHOULD be possible to limit the impact of badly behaving
P2PSIP nodes on the overall system security. There SHOULD be an
option to identify malfunctioning or badly behaving nodes, and
exclude or reject them from the P2PSIP system.
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8. Security Considerations
This memo discusses security threats in P2PSIP overlay networks.
Security aspects are discussed throughout the document. However,
this document does not introduce any security risk by itself.
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9. IANA Considerations
There are no IANA considerations associated to this memo.
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10. Acknowledgments
The authors would like to thank the many people of the IETF P2PSIP WG
that have contributed to discussions and provided input invaluable in
assembling this document.
Acknowledgement is also given to Jan-Erik Ekberg and Pekka Laitinen,
both with Nokia, and to Jiang Xingfeng with Huawei for their work on
earlier versions of the documents now incorporated into this draft.
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11. Changes
11.1. Revision 4
In this revision, the following changes were made:
o Author team was modified.
o Author Note was changed to reflect that changes will be made based
on new RELOAD draft.
o Various wording changes based on comments from Christian Schmidt.
o The migration of references was begun to a form where they will
stay up-to-date when new versions of the document are created.
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12. Appendix: Security threats
This section analyses security threats in the Peer-to-Peer SIP
architecture.
12.1. Replay Attacks
Replay attacks are a form of network attacks where a valid data
transmission is repeated or delayed. A badly behaving node may take
an older message sent by another node, resend it to the overlay, and
thus replace any newer data with the old information present in this
message. During those procedures, an attacker may be able to enroll
credentials for himself, or replace existing entry in the P2PSIP
overlay by an older entry. Thus, the architecture must consider this
issue in the process of both enrollment and modification of P2PSIP
resource (user) records in a P2PSIP overlay.
This is especially applicable to P2PSIP overlays that use the
recursive routing style. In the recursive routing style, data sent
in a PUT request traverses many peers in the overlay. If there is no
protection against the replay attacks any peer that forwards the
request may store a copy of the request and resend the captured
request corrupting data stored in the overlay.
12.2. Message Insertion, Modification, Deletion
The message insertion, modification, and deletion attacks are where
an attacker is able to alter the messages being exchanged between two
end points.
P2PSIP peers connect to other peers to form the P2PSIP overlay
network. Typically peers provide storage, routing and bootstrap
services for other peers and clients. They allow P2PSIP entities to
PUT information to or GET information from the P2PSIP overlay
network. In the P2PSIP overlay that allows for a recursive routing,
peers are responsible for forwarding messages (requests and
responses) received from P2PSIP network entities to other peers.
Depending on the size of the overlay a single message can be
forwarded by many peers before it reaches a destination. In the
iterative routing peers are responsible for redirecting the requests
to other peers. They do not forward the requests to other peers.
They respond to a request originator with an address of a peer that
should be contacted in the next step. In such an environment a badly
behaving peer may:
o modify incoming messages,
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o discard incoming messages (the peer can discard requests and
responses it is supposed to forward),
o generate incorrect responses to requests that are directed to some
other nodes.
The first bullet point describes the attack that allows the peer to
cause the overlay to store unauthorized or outdated information in
the resource (user) records or return corrupted data to the
originator of the GET request (a peer or client). The peer may
change the data record in the overlay by changing incoming PUT
messages or modify result of the GET operation by modifying incoming
GET responses. With this type of attack the integrity of the P2PSIP
system can become compromised.
The middle bullet point is related not only to attacks that allow a
malicious peer to prevent access to a P2PSIP resource (user) record,
but also to attacks that can degrade the performance of the P2PSIP
system making it useless from the end-user perspective. The second
problem is of high importance in P2PSIP overlays that store user's
reachability data which is much more time-critical than content
stored in file sharing networks.
The attack described in the last bullet above may lead to a requestor
receiving corrupted data e.g. a connectivity information that points
to some other node. This may happen if a malicious peer can respond
to incoming requests that are directed to another peer.
Besides peers may act as relays relaying traffic between two P2PSIP
network entities or act as a SIP proxy and a SIP registrar.
Providing those services a malicious peer may perform a similar
attacks as described above. Let us consider the following deployment
scenario where some peers act as SIP registrars or/and SIP proxies
and allow a conventional SIP UA to access resources of the P2PSIP
overlay network. An unmodified SIP UA sends an SIP Invite request
towards an unknown peer that acts as a SIP proxy. If the SIP
messages are not cryptographically protected, this peer may act
maliciously and proxy a request to other than intended node or modify
SDP messages in order to stay on the media path. Similarly a peer
that acts as a SIP Registrar may modify registration information
before it sends it to a peer that is responsible for storing the
P2PSIP user record of a registering SIP UA. Those attacks do not
have impact on the integrity of the overlay. Nevertheless those
attacks must be addressed by designers of service specific protocols
such as SIP [RFC3261].
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12.3. Man-In-The-Middle
In man-in-the-middle (m-i-m) attacks a malicious node can hijack a
connection established between two legitimate nodes, or just listen
and/or modify messages exchanged between two nodes. In contrast to
the attacks presented in Section 3.2 man-in-the middle attacks are
prevalent in pairing and authentication procedures.
The m-i-m threat can be mitigated by using well-established
authentication protocols. The authentication protocols may be used
to verify if a certain P2PSIP entity is the entity it claims to be,
for example if it is really a peer that is identified by a certain
peer ID. The authentication protocols can also be used to verify if
a particular P2PSIP entity belongs to a particular overlay or not.
However, authentication protocols cannot fully mitigate all of the
attacks presented in Section 3.2. There can be malicious peers that
are authorised overlay participants with a particular peer
identifiers.
If a bootstrap process is fully decentralised and a bootstrap node is
not trusted or authentication of the bootstrap node is not possible,
then the joining node can easily be attacked, e.g. it may be
redirected to another overlay or a part of the legacy overlay that is
controlled by the attacker. However if it is possible to
authenticate a particular peer in the overlay the joining peer may
use P2P specific mechanisms to detect if it is redirected to the
right overlay or the right place in the overlay.
Conventional SIP proxy and SIP registrars are servers maintained by a
service provider. If a user trust a service provider he also trusts
servers the service provider maintains. In P2PSIP SIP proxies and
registrars can be maintained by users themselves (they can be
collocated with peers). In a distributed environment it is very
difficult to trust all of peers in the overlay. Without an efficient
verification mechanism that allows to verify which peers are be
trusted, peers that act as SIP proxies and registrars may easily
perform m-i-m attacks. The problem must be solved by SIP designers
as well as by the P2PSIP community.
12.4. Offline Cryptographic Attacks
The incentive to break a secure system dominates the effort to do so.
It is likely that P2PSIP systems do not pose a likely target for
attacks, and if state-of-the art security methods are used, the
needed effort to break the system by breaking cryptography is very
likely to be higher than by finding and exploiting software errors
and vulnerabilities.
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12.5. Unauthorized Usage
The basic notions of authentication and authorization, when
implemented correctly and consistently SHOULD protect against
unauthorized usage of the P2PSIP system. However, the
trustworthiness of an identity may be weak i.e. the enrollment system
might be fairly open and allow devices and persons that wish to
attack the system. Thus, there is a significant threat of attacks
from within the system.
A malicious peer may do a multitude of attacks towards the overlay
including:
o ignoring, changing, and deleting records in DHT that is it
responsible for,
o misbehaving during data lookups (ie, giving wrong node addresses,
discarding queries).
The first bullet point is related to attacks that may cause DHT to
contain unauthorized, outdated information and/or miss information
about users or resources. Each peer is responsible for a part of the
hash space. Peers store resource (user) records that fall into their
part of the hash space. A malicious peer may modify or delete
resource (user) records it is supposed to store. It may also reply
with incorrect information to the GET requests addressed to resource
(user) records it is responsible for. In addition it may ignore any
record updates. These attacks are not limited to peers that are
responsible for primary copies of resource (user) records. They are
also related to peers that store replicas of resource (user) records.
Besides a bootstrap node may also respond with wrong bootstraping
information.
The second bullet point addresses attacks that may impact correctness
of routing mechanisms. If the recoursive routing is used a malicious
peer can forward messages to another malicious node rather than
forwarding the messages according to the legitimate routing
information. This may also impact the iterative routing being
corrupted when the peer redirects the requester to a malicious node.
12.6. Inappropriate Usage
The P2PSIP essentially provides a distributed storage for P2PSIP
resource (user) records. The data stored in the distributed database
can be used in an inappropriate manner. If there is no access
control to a resource (user) records stored in the overlay and any
node can update or retrieve information stored in the overlay. An
attacker may request data stored in the P2PSIP resource (user)
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records and perform inappropriate usage attacks. Besides the
attacker may also update entries of other users or resources.
The individual services provided by P2PSIP (messaging, real-time
communication) have their respective threat models regarding
inappropriate use (Spam, viruses, ...) but these can be considered
out of scope for this document.
12.7. Denial of Service
In the P2PSIP architecture [1], the P2PSIP resource (user) records
are not maintained in a central, trustworthy storage system, rather
they are distributed among peers participating in the system.
Routing, relaying, SIP proxy and registrar services are also
distributed among P2PSIP entities. In cases where authentication in
the P2PSIP overlay is weak or where the system is fairly open to new
participants the "infiltration" is trivial (e.g., Sybil attack).
If peers in the P2PSIP overlay can freely choose peer IDs or/and
easily modify previously selected peer IDs the attacker may use join-
leave attacks to place a malicious peer intentionally at any location
in overlay. Placing the peer at any location allows an attacker to
obtain control of the location in the overlay where the attacked user
or resource is registered. A malicious peer may discard, modify the
data it is supposed to store and may discard lookup requests or reply
with incorrect entries to the incoming requests.
The attacker may also try to register a large number of resources to
the P2PSIP overlay increasing processing load on peers that are
responsible for storing the resources and limiting the overall
capacity of the P2PSIP overlay network. It may also try to register
all popular names preventing the name holders from registering their
preferred URIs.
Another critical point where a D-o-S attack can be mounted is the
enrollment system.
12.8. Communication security threats
The main places where communication security becomes an issue in the
P2PSIP context is the enrollment process and the communication
between endpoints. The last ones are subject to all typical threats
in this domain, however they have been individually considered in the
earlier sections of this chapter.
This document assumes that the actual SIP service implementation
provides its own communication security, and that P2PSIP adds to that
only in providing a means for the communication endpoints to
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establish a shared key for further security needs. Otherwise, the
communication security threats in that domain is out-of-scope for
this discussion.
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13. Normative References
[1] Bryan, D., Matthews, P., Shim, P., and D. Willis,
"Concepts and Terminology for Peer to Peer SIP",
draft-ietf-p2psip-concepts-02.txt (work in progress),
April 2007.
[I-D.bryan-p2psip-app-scenarios]
Bryan, D., Shim, E., Lowekamp, B., and S. Dawkins,
"Application Scenarios for Peer-to-Peer Session Initiation
Protocol (P2PSIP)", draft-bryan-p2psip-app-scenarios-00
(work in progress), November 2007.
[I-D.bryan-p2psip-requirements]
Bryan, D., "P2PSIP Protocol Framework and Requirements",
draft-bryan-p2psip-requirements-00 (work in progress),
July 2007.
[I-D.ietf-p2psip-base]
Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)
Base Protocol", draft-ietf-p2psip-base-00 (work in
progress), October 2008.
[I-D.ietf-p2psip-sip]
Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
H. Schulzrinne, "A SIP Usage for RELOAD",
draft-ietf-p2psip-sip-00 (work in progress), October 2008.
[I-D.song-p2psip-security-eval]
Yongchao, S., Zhao, B., Jiang, X., and J. Haifeng, "P2PSIP
Security Analysis and Evaluation",
draft-song-p2psip-security-eval-00 (work in progress),
February 2008.
[I-D.zheng-p2psip-diagnose]
Yongchao, S., Zhang, H., and X. Jiang, "Diagnose P2PSIP
Overlay Network Failures", draft-zheng-p2psip-diagnose-02
(work in progress), July 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
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Authors' Addresses
Song Haibin
Huawei
Baixia Road No. 91
Nanjing, Jiangsu Province 210001
P.R.China
Phone: +86-25-84565081
Fax: +86-25-84565070
Email: melodysong@huawei.com
Marcin Matuszewski
Nokia
P.O.Box 407
NOKIA GROUP, FIN 00045
Finland
Email: marcin.matuszewski@nokia.com
Dan York
Voxeo Corporation
Keene, NH
USA
Phone: +1-407-455-5859
Email: dyork@voxeo.com
URI: http://www.voxeo.com/
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