Internet Engineering Task Force N. Elkins
Internet-Draft Inside Products, Inc.
Intended status: Standards Track M. Ackermann
Expires: 8 April 2025 BCBS Michigan
A. Deshpande
NITK Surathkal/Google
T. Pecorella
University of Florence
A. Rashid
Politecnico di Bari
5 October 2024
IPv6 Performance and Diagnostic Metrics Version 2 (PDMv2) Destination
Option
draft-ietf-ippm-encrypted-pdmv2-09
Abstract
RFC8250 describes an optional Destination Option (DO) header embedded
in each packet to provide sequence numbers and timing information as
a basis for measurements. As this data is sent in clear-text, this
may create an opportunity for malicious actors to get information for
subsequent attacks. This document defines PDMv2 which has a
lightweight handshake (registration procedure) and encryption to
secure this data. Additional performance metrics which may be of use
are also defined.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://ameyand.github.io/PDMv2/draft-elkins-ippm-encrypted-
pdmv2.html. Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-ippm-encrypted-pdmv2/.
Discussion of this document takes place on the IP Performance
Measurement Working Group mailing list (mailto:ippm@ietf.org), which
is archived at https://mailarchive.ietf.org/arch/browse/ippm/.
Subscribe at https://www.ietf.org/mailman/listinfo/ippm/.
Source for this draft and an issue tracker can be found at
https://github.com/ameyand/PDMv2.
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Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 8 April 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 4
3. PDMv2 Destination Options . . . . . . . . . . . . . . . . . . 4
3.1. Destinations Option Header . . . . . . . . . . . . . . . 4
3.2. Metrics information in PDMv2 . . . . . . . . . . . . . . 4
3.3. PDMv2 Layout . . . . . . . . . . . . . . . . . . . . . . 6
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Client - Server Negotiation . . . . . . . . . . . . . . . 9
5.2. Implementation Guidelines . . . . . . . . . . . . . . . . 10
5.2.1. Use Case 1: Server does not understand PDM or
PDMv2 . . . . . . . . . . . . . . . . . . . . . . . . 11
5.2.2. Use Case 2: Server does not allow PDM Option (PDM or
PDMv2) . . . . . . . . . . . . . . . . . . . . . . . 11
6. Security Goals . . . . . . . . . . . . . . . . . . . . . . . 11
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6.1. Security Goals for Confidentiality . . . . . . . . . . . 12
6.2. Security Goals for Integrity . . . . . . . . . . . . . . 12
6.3. Security Goals for Authentication . . . . . . . . . . . . 12
6.4. Cryptographic Algorithm . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7.1. Limited Threat Model . . . . . . . . . . . . . . . . . . 13
7.1.1. Passive attacks with unencrypted PDMv2 . . . . . . . 13
7.1.2. Passive attacks with encrypted PDMv2 . . . . . . . . 14
7.1.3. Active attacks with unencrypted PDMv2 . . . . . . . . 15
7.1.4. Active attacks with encrypted PDMv2 . . . . . . . . . 16
7.2. Topological considerations . . . . . . . . . . . . . . . 17
7.3. Further mitigations . . . . . . . . . . . . . . . . . . . 17
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 17
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Sample Implementation of Registration . . . . . . . 20
A.1. Overall summary . . . . . . . . . . . . . . . . . . . . . 20
A.2. High level flow . . . . . . . . . . . . . . . . . . . . . 20
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 20
Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
The current Performance and Destinations Metrics (PDM) is an IPv6
Destination Options header which provides information based on the
metrics like Round-trip delay and Server delay. This information
helps to measure the Quality of Service (QoS) and to assist in
diagnostics. However, there are potential risks involved
transmitting PDM data during a diagnostics session.
PDM metrics can help an attacker understand about the type of machine
and its processing capabilities. For example, the operational
capabilities of either the client or server end hosts such as
processing speed -- that is, if the system in question is very fast
system or an older, slower device.
Inferring from the PDM data, the attack can launch a timing attack.
For example, if a cryptographic protocol is used, a timing attack may
be launched against the keying material to obtain the secret.
PDM metrics may also help the attacker find out about the network
speed or capabilities of the network path. For example, are there
delays or blockages? Are there alternate or multiple paths?
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Along with this, PDM does not provide integrity. It is possible for
a Machine-In-The-Middle (MITM) node to modify PDM headers leading to
incorrect conclusions. For example, during the debugging process
using PDM header, it can mislead by showing there are no unusual
server delays.
PDMv2 is an IPv6 Destination Options Extension Header which adds
confidentiality, integrity and authentication to PDM.
The procedures specified in RFC8250 for header placement,
implementation, security considerations and so on continue to apply
for PDMv2.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. PDMv2 Destination Options
3.1. Destinations Option Header
The IPv6 Destination Options extension header [RFC8200] is used to
carry optional information that needs to be examined only by a
packet's destination node(s). The Destination Options header is
identified by a Next Header value of 60 in the immediately preceding
header and is defined in RFC 8200 [RFC8200]. The IPv6 PDMv2
destination option is implemented as an IPv6 Option carried in the
Destination Options header.
3.2. Metrics information in PDMv2
The IPv6 PDMv2 destination option contains the following base fields:
SCALEDTLR: Scale for Delta Time Last Received
SCALEDTLS: Scale for Delta Time Last Sent
GLOBALPTR: Global Pointer
PSNTP: Packet Sequence Number This Packet
PSNLR: Packet Sequence Number Last Received
DELTATLR: Delta Time Last Received
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DELTATLS: Delta Time Last Sent
PDMv2 adds a new metric to the existing PDM [RFC8250] called the
Global Pointer. The existing PDM fields are identified with respect
to the identifying information called a "5-tuple".
The 5-tuple consists of:
SADDR: IP address of the sender
SPORT: Port for the sender
DADDR: IP address of the destination
DPORT: Port for the destination
PROTC: Upper-layer protocol (TCP, UDP, ICMP, etc.)
Unlike PDM fields, Global Pointer (GLOBALPTR) field in PDMv2 is
defined for the SADDR type for the node. Two SADDR address types are
used:
a) Link-Local
b) Global Unicast
Hence, there are two Global Pointers.
The Global Pointer is treated as a common entity over all the
5-tuples with the same SADDR type. It is initialised to the value 1
and increments for every packet sent. Global Pointer provides a
measure of the amount of IPv6 traffic sent by the PDMv2 node.
When the SADDR type is Link-Local, the PDMv2 node sends Global
Pointer defined for Link-Local addresses, and when the SADDR type is
Global Unicast, it sends the one defined for Global Unicast
addresses.
The reason for the Global Pointers is to provide a rough estimation
of the load on the node in question. That is, if the node is sending
many other packets to other destinations at the same time as this
particular session. Given that goal, if we combine the Link Local
and Global Unicast, the traffic traversing the path over the LAN or
VLAN (Link Local) would be combined with the traffic traversing the
path over the internet or wide area network. The nature of Link-
Local and Global Unicast traffic is quite different, hence the two
separate counters.
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3.3. PDMv2 Layout
PDMv2 has two different header formats corresponding to whether the
metric contents are encrypted or unencrypted. The difference between
the two types of headers is determined from the Options Length value.
Following is the representation of the unencrypted PDMv2 header:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | Vrsn | Epoch |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PSN This packet |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PSN Last Received |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global Pointer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ScaleDTLR | ScaleDTLS | Reserved |
|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Delta Time Last Received | Delta Time Last Sent |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Following is the representation of the encrypted PDMv2 header:
0 1 2 3
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | Vrsn | Epoch |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PSN This Packet |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encrypted PDM Data :
: (16 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
0x0F
8-bit unsigned integer. The Option Type is adopted from RFC 8250
[RFC8250].
Option Length
0x22: Unencrypted PDM
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0x22: Encrypted PDM
8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields.
Version Number
0x2
4-bit unsigned number.
Epoch
12-bit unsigned number.
Epoch field is used to indicate the valid SessionTemporaryKey.
Packet Sequence Number This Packet (PSNTP)
32-bit unsigned number.
This field is initialized at a random number and is incremented
sequentially for each packet of the 5-tuple.
This field + Epoch are used in the Encrypted PDMv2 as the
encryption nonce. The nonce MUST NOT be reused in different
sessions.
Packet Sequence Number Last Received (PSNLR)
32-bit unsigned number.
This field is the PSNTP of the last received packet on the
5-tuple.
Global Pointer
32-bit unsigned number.
Global Pointer is initialized to 1 for the different source
address types and incremented sequentially for each packet with
the corresponding source address type.
This field stores the Global Pointer type corresponding to the
SADDR type of the packet.
Scale Delta Time Last Received (SCALEDTLR)
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8-bit unsigned number.
This is the scaling value for the Delta Time Last Sent (DELTATLS)
field.
Scale Delta Time Last Sent (SCALEDTLS)
8-bit unsigned number.
This is the scaling value for the Delta Time Last Sent (DELTATLS)
field.
Reserved Bits
16-bits.
Reserved bits for future use. They MUST be set to zero on
transmission and ignored on receipt per [RFC3552].
Delta Time Last Received (DELTATLR)
16-bit unsigned integer.
The value is set according to the scale in SCALEDTLR.
Delta Time Last Received = (send time packet n - receive time
packet (n - 1))
Delta Time Last Sent (DELTATLS)
16-bit unsigned integer.
The value is set according to the scale in SCALEDTLS.
Delta Time Last Sent = (receive time packet n - send time packet
(n - 1))
4. Terminology
* Endpoint Node: Creates cryptographic keys in collaboration with a
partner.
* Client: An Endpoint Node which initiates a session with a
listening port on another Endpoint Node and sends PDM data.
* Server: An Endpoint Node which has a listening port and sends PDM
data to another Endpoint Node.
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Note: a client may act as a server (have listening ports).
* Public and Private Keys: A pair of keys that is used in asymmetric
cryptography. If one is used for encryption, the other is used
for decryption. Private Keys are kept hidden by the source of the
key pair generator, but the Public Key may be known to everyone.
In this document, the Public Key is represented as pkX and the
Private Key as skX (where X can be any client or server).
* Pre-shared Key (PSK): A symmetric key. Uniformly random
bitstring, shared between any Client or any Server or a key shared
between an entity that forms client-server relationship. This
could happen through an out-of band mechanism: e.g., a physical
meeting or use of another protocol.
* Shared Secret: A piece of data, known only to the parties
involved.
* SessionTemporaryKey: A A temporary key used to secure data for
only the current session
5. Protocol Flow
The protocol will proceed in 2 steps.
Step 1: Creation of cryptographic secrets between Server and Client.
This includes the creation of pkX and skX.
Step 2: PDM data flow between Client and Server.
These steps MAY be in the same session or in separate sessions. That
is, the cryptographic secrets MAY be created beforehand and used in
the PDM data flow at the time of the "real" data session.
After-the-fact (or real-time) data analysis of PDM flow may occur by
network diagnosticians or network devices. The definition of how
this is done is out of scope for this document.
5.1. Client - Server Negotiation
The two entities exchange a set of data to ensure the respective
identities. This could be done via a TLS or other session. The
exact nature of the identity verification is out-of-scope for this
document.
They use Hybrid Public-Key Encryption scheme (HPKE) Key Encapsulation
Mechanism (KEM) to negotiate a "SharedSecret".
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Each Client and Server derive a "SessionTemporaryKey" by using HPKE
Key Derivation Function (KDF), using the following inputs:
* The "SharedSecret".
* The 5-tuple (SrcIP, SrcPort, DstIP, DstPort, Protocol) of the
communication.
* An Epoch.
The Epoch SHOULD be initialized to zero. A change in the Epoch
indicates that the SessionTemporaryKey has been rotated.
The Epoch MUST be incremented when the Packet Sequence Number This
Packet (PSNTP) is rolled over. It MAY be incremented earlier,
depending on the implementation and the security considerations.
The sender MUST NOT create two packets with identical PSNTP and
Epoch.
When the Epoch overflows, then collection of PDM data for this
session will be stopped. An error message MUST be sent as per
[RFC9180]: MessageLimitReachedError: Context AEAD sequence number
overflow.
5.2. Implementation Guidelines
How should a network administrator decide whether a client should use
PDM, unencrypted PDMv2, or encrypted PDMv2? This decision is a
network policy issue. The administrator must be aware that PDM or
unencrypted PDMv2 might expose too much information to malicious
parties.
That said, if the network administrator decides that taking such a
risk within their network is acceptable, then they should make the
decision that is appropriate for their network.
Alternatively, the network administrator might choose to create a
policy that prohibits the use of PDM or unencrypted PDMv2 on their
network. The implementation SHOULD provide a way for the network
administrator to enforce such a policy.
The server and client implementations SHOULD support PDM, unencrypted
PDMv2, and encrypted PDMv2. If a client chooses a certain mechanism
(e.g., PDM), the server MAY respond with the same mechanism, unless
the network administrator has selected a policy that only allows
certain mechanisms on their network.
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5.2.1. Use Case 1: Server does not understand PDM or PDMv2
If a client sends a packet with PDM or PDMv2 and the server does not
have code which understands the header, the packet is processed
according to the Option Type which is defined in RFC8250 and is in
accordance with RFC8200.
The Option Type identifiers is coded to skip over this option and
continue processing the header.
5.2.2. Use Case 2: Server does not allow PDM Option (PDM or PDMv2)
If a client sends a packet with a PDM option which does not match the
network policy, then the PDM option MUST be ignored and processing
continue normally. The server SHOULD log such occurrences.
Filtering at routers per [RFC9288] on filtering of IPv6 extension
headers may impact the receipt of PDM / PDMv2.
6. Security Goals
As discussed in the introduction, PDM data can represent a serious
data leakage in presence of a malicious actor.
In particular, the sequence numbers included in the PDM header allows
correlating the traffic flows, and the timing data can highlight the
operational limits of a server to a malicious actor. Moreover,
forging PDM headers can lead to unnecessary, unwanted, or dangerous
operational choices, e.g., to restore an apparently degraded Quality
of Service (QoS).
Due to this, it is important that the confidentiality and integrity
of the PDM headers is maintained. PDM headers can be encrypted and
authenticated using the methods discussed in Section 5.4, thus
ensuring confidentiality and integrity. However, if PDM is used in a
scenario where the integrity and confidentiality is already ensured
by other means, they can be transmitted without encryption or
authentication. This includes, but is not limited to, the following
cases:
a) PDM is used over an already encrypted medium (For example VPN
tunnels).
b) PDM is used in a link-local scenario.
c) PDM is used in a corporate network where there are security
measures strong enough to consider the presence of a malicious
actor a negligible risk.
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6.1. Security Goals for Confidentiality
PDM data MUST be kept confidential between the intended parties,
which includes (but is not limited to) the two entities exchanging
PDM data, and any legitimate party with the proper rights to access
such data.
6.2. Security Goals for Integrity
An implementation SHOULD attempt to detect if PDM data is forged or
modified by a malicious entity. In other terms, the implementation
should attempt to detect if a malicious entity has generated a valid
PDM header impersonating an endpoint or modified a valid PDM header.
6.3. Security Goals for Authentication
An unauthorized party MUST NOT be able to send PDM data and MUST NOT
be able to authorize another entity to do so. Alternatively, if
authentication is done via any of the following, this requirement MAY
be considered to be met.
a) PDM is used over an already authenticated medium (For example,
TLS session).
b) PDM is used in a link-local scenario.
c) PDM is used in a corporate network where security measures are
strong enough to consider the presence of a malicious actor a
negligible risk.
6.4. Cryptographic Algorithm
Symmetric key cryptography has performance benefits over asymmetric
cryptography; asymmetric cryptography is better for key management.
Encryption schemes that unite both have been specified in [RFC1421],
and have been participating practically since the early days of
public-key cryptography. The basic mechanism is to encrypt the
symmetric key with the public key by joining both yields. Hybrid
public-key encryption schemes (HPKE) [RFC9180] used a different
approach that generates the symmetric key and its encapsulation with
the public key of the receiver.
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It is RECOMMENDED to use the HPKE framework that incorporates key
encapsulation mechanism (KEM), key derivation function (KDF) and
authenticated encryption with associated data (AEAD). These multiple
schemes are more robust and significantly more efficient than other
schemes. While the schemes may be negotiated between communicating
parties, it is RECOMMENDED to use default encryption algorithm for
HPKE AEAD as AES-128-GCM.
7. Security Considerations
PDMv2 carries metadata, including information about network
characteristics and end-to-end response time. This metadata is used
to optimize communication. However, in the context of passive
attacks, the information contained within PDMv2 packets can be
intercepted by an attacker, and in the context of active attacks the
metadata can be modified by an attacker.
In the following we will briefly outline the threat model and the
associated security risks, using RFC3552 terminology and
classification.
7.1. Limited Threat Model
We assume that the attacker does not control the endpoints, but it
does have a limited control of the network, i.e., it can either
monitor the communications (leading to passive attacks), or modify/
forge packets (active attacks).
7.1.1. Passive attacks with unencrypted PDMv2
Passive Attack Scenario: In a passive attack, the attacker seeks to
obtain information that the sender and receiver of the communication
would prefer to keep private. In this case, the attacker is not
altering the packets but is intercepting and analyzing them. Here's
how this can happen in the context of unencrypted PDMv2:
a. Being on the same LAN: The simplest way for an attacker to launch
a passive attack is to be on the same Local Area Network (LAN) as
the victim. Many LAN configurations, such as Ethernet, 802.3,
and FDDI, allow any machine on the network to read all traffic
destined for any other machine on the same LAN. This means that
if PDM packets are sent over the LAN, the attacker can capture
them.
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b. Control of a Host in the Communication Path: If the attacker has
control over a host that lies in the communication path between
two victim machines, they can intercept PDM packets as they pass
through this compromised host. This allows the attacker to
collect metadata without being on the same LAN as the victim.
c. Compromising Routing Infrastructure: In some cases, attackers may
actively compromise the routing infrastructure to route traffic
through a compromised machine. This can facilitate a passive
attack on victim machines. By manipulating routing, the attacker
can ensure that PDMv2 packets pass through their controlled node.
d. Wireless Networks: Wireless communication channels, such as those
using 802.11 (Wi-Fi), are particularly vulnerable to passive
attacks. Since data is broadcast over well-known radio
frequencies, an attacker with the ability to receive those
transmissions can intercept PDMv2 packets. Weak or ineffective
cryptographic protection in wireless networks can make it easier
for attackers to capture this data.
Goal of Passive Attack: In a passive attack, the attacker's goal is
to obtain sensitive information from intercepted packets. In the
case of PDMv2, this information may include network characteristics,
end-to-end response times, and potentially any other metadata that is
transmitted. This information can be valuable to the attacker for
various purposes, such as analyzing network performance or gaining
insights into communication patterns.
In summary, within the limited Internet threat model described in
RFC3552, attackers with the ability to intercept packets can conduct
passive attacks to capture metadata carried in IPv6 unencrypted PDMv2
packets. This information can be useful for the attacker, even
without actively altering the communication. Security measures, such
as encryption and network segmentation, are important countermeasures
to protect against such passive attacks.
7.1.2. Passive attacks with encrypted PDMv2
Passive Attack Scenario: An attacker is trying to seek useful
information from encrypted PDMv2 packets happening between two
different entities. Encrypted PDMv2 has most of the metadata fields
encrypted except for PSNTP which is also used as a nonce in HPKE
AEAD.
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Goal of Passive Attack: In this attack, the attacker is trying to
obtain the order in which the packets were sent from the sender to
the receiver for different flows. The amount of information gathered
by the attacker is similar, to some extent, to the ones available by
inspecting the TTCP sequence number, which is also usually not
protected. Therefore, we consider this information leak acceptable.
Nevertheless, this point should be noted if complete traffic
obfuscation (including packet reordering) is necessary. In these
cases it is suggested to use IPSec ESP [RFC4303] in tunnel mode (in
which case the PDMv2 can be used unencrypted).
7.1.3. Active attacks with unencrypted PDMv2
There are also active attacks within the context of the limited
Internet threat model defined in [RFC3552]. In this model, active
attacks involve an attacker writing data to the network, and the
attacker can forge packets and potentially manipulate the behavior of
devices or networks. Let's break down how message modification,
deletion, or insertion by attackers using the unencrypted IPv6
Performance and Destination option v2 (PDMv2) fits into this threat
model:
1. Message Modification Attack:
In a message modification attack, the attacker intercepts a
message, modifies its content, and then reinserts it into the
network. This attack is significant because it allows the
attacker to tamper with the integrity of the data being
transmitted.
Example: Suppose an attacker intercepts an IPv6 packet containing
unencrypted PDMv2 information that includes network and end-to-
end response time metadata. The attacker modifies this
information, such as altering the response time data or inserting
false information. When this modified packet reaches its
destination, the receiving device or network may act based on
this malicious information, potentially leading to degraded
performance, incorrect network management decisions, wrong
performance data collection, etc. A direct consequence of
modifying the performance data could be, for example, to hide an
ongoing QoS violation, or to create a fake QoS violation, with
consequences on the violation of Service Level Agreements.
2. Message Deletion Attack:
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In a message deletion attack, the attacker removes a message from
the network. This attack can be used in conjunction with other
attacks to disrupt communication or achieve specific objectives.
Example: Consider a scenario where an attacker deletes certain
IPv6 packets that contain unencrypted PDMv2 information, or
deletes the PDM header from the packet. If the PDMv2 is used for
network monitoring or quality of service (QoS) management, the
deletion of these packets can cause the monitoring system to miss
critical data, potentially leading to inaccurate network
performance analysis or decisions.
3. Message Insertion Attack:
In a message insertion attack, the attacker forges a message and
injects it into the network.
Example: An attacker could forge IPv6 packets containing
unencrypted PDMv2 data with fake source addresses and inject them
into the network. If PDM is used for making routing or resource
allocation decisions, these injected packets can influence the
network's behavior, potentially causing it to take suboptimal
routes or allocate resources incorrectly.
All these attacks are considered active attacks because the attacker
actively manipulates network traffic, and they can potentially spoof
the source address to disguise their identity. In the limited
Internet threat model defined in [RFC3552], it is assumed that
attackers can forge packets and carry out such active attacks. These
attacks highlight the importance of securing network protocols,
authenticating messages, and implementing proper security measures to
protect against them.
7.1.4. Active attacks with encrypted PDMv2
Encrypted PDMv2 provides inherent protection against active attacks
like Message Modification by providing integrity. If either of the
sequence number or encrypted PDMv2 contents are modified then
decryption will fail.
Message Deletion Attack can be performed for encrypted PDMv2
similarly to unencrypted PDMv2.
Impersonation Attack: Encrypted PDMv2 relies on a shared secret
negotiated by an external protocol (e.g., TLS). If key exchange does
have authentication check, then an adversary who impersonates the
host can derive a key with the destination client and potentially
perform all the above active attacks even on encrypted PDMv2.
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7.2. Topological considerations
The same topological considerations highlighted in [RFC3552] applies
in this context. Passive attacks and active attacks where the
messages need to be modified or deleted are more likely if the
attacker is on-path, while message insertion attacks are more likely
when the attacker is off-path but can happen also when the attacker
is on-path. Link-local attacks can be considered as a special case
of on-path for PDM, i.e., for PDM a link-local attacker has no
special privileges with respect to an on-path attacker.
7.3. Further mitigations
PDM includes cryptographic mechanisms to mitigate passive and active
attacks. As a further security mechanism to protect from active
attacks, it is possible for an implementation to include logging of
anomalous events, e.g.:
* Missing PDM header when expected (counteracts the Message
Deletion).
* Unusual variations of the PDM data (counteracts the Message
Modification)
* Accept the PDM data only if the application level accepts the
packet payload (counteracts the Message Insertion)
* Monitor repeated or unexpected PDM data (counteracts replay
attacks).
Security considerations about HPKE are addressed in RFC 9180.
Security considerations about PDM are addressed in RFC 8250.
Security considerations about destination objects are addressed in
RFC 8200.
8. Privacy Considerations
Encryption plays a crucial role in providing privacy as defined by
[RFC6973], especially when metadata sniffing is a concern.
[RFC6973], titled "Privacy Considerations for Internet Protocols,"
outlines the importance of protecting users' privacy in the context
of various Internet protocols, including IPv6. When metadata like
network and end-to-end response time is at risk of being observed by
attackers, eavesdroppers, or observers, encryption can help mitigate
the privacy risks. Here's how encryption achieves this:
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a) Confidentiality: Encryption ensures that the actual content of
the communication remains confidential. Even if attackers or
observers intercept the data packets, they won't be able to
decipher the information without the encryption key. In the case
of IPv6 Performance and Destination Option (PDM), the still-
visible, non-encrypted metadata is still visiblenegligible, and
does not poses confidentiality
b) Content Protection: Metadata, such as network and end-to-end
response time, may reveal sensitive information about the
communication. By encrypting the content, encryption mechanisms
help protect this sensitive data from being exposed. Observers
may still see that communication is happening, but they won't be
able to glean meaningful information from the metadata.
c) Integrity: Encryption often includes mechanisms to ensure data
integrity. It allows the recipient to verify that the received
data has not been tampered with during transit. This helps
protect against attackers who might try to manipulate the
metadata.
It's important to note that while encryption enhances privacy by
protecting the content of communication, metadata still poses some
challenges. Metadata, such as the fact that communication is
occurring and the parties involved, can be revealing. To address
this, additional techniques, like traffic obfuscation, may be used to
hide metadata patterns. However, complete metadata privacy can be
challenging to achieve, especially when communication protocols
inherently require some level of metadata exchange.
Specifically, enabling PDM only for a specific set of flows can pose
a risk of highlighting their presence between two parties. As a
mitigation technique, it is suggested to obfuscate the events, for
example by enabling PDM on more flows than strictly necessary.
9. IANA Considerations
No action is needed by IANA.
10. Contributors
The authors wish to thank NITK Surathkal for their support and
assistance in coding and review. In particular Dr. Mohit Tahiliani
and Abhishek Kumar (now with Google). Thanks also to Priyanka Sinha
for her comments. Thanks to the India Internet Engineering Society
(iiesoc.in), in particular Dhruv Dhody, for his comments and for
providing the funding for servers needed for protocol development.
Thanks to Balajinaidu V, Amogh Umesh, and Chinmaya Sharma of NITK for
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developing the PDMv2 implementation for testing.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/rfc/rfc3552>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/rfc/rfc8200>.
[RFC8250] Elkins, N., Hamilton, R., and M. Ackermann, "IPv6
Performance and Diagnostic Metrics (PDM) Destination
Option", RFC 8250, DOI 10.17487/RFC8250, September 2017,
<https://www.rfc-editor.org/rfc/rfc8250>.
11.2. Informative References
[RFC1421] Linn, J., "Privacy Enhancement for Internet Electronic
Mail: Part I: Message Encryption and Authentication
Procedures", RFC 1421, DOI 10.17487/RFC1421, February
1993, <https://www.rfc-editor.org/rfc/rfc1421>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/rfc/rfc4303>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/rfc/rfc6973>.
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[RFC9180] Barnes, R., Bhargavan, K., Lipp, B., and C. Wood, "Hybrid
Public Key Encryption", RFC 9180, DOI 10.17487/RFC9180,
February 2022, <https://www.rfc-editor.org/rfc/rfc9180>.
[RFC9288] Gont, F. and W. Liu, "Recommendations on the Filtering of
IPv6 Packets Containing IPv6 Extension Headers at Transit
Routers", RFC 9288, DOI 10.17487/RFC9288, August 2022,
<https://www.rfc-editor.org/rfc/rfc9288>.
Appendix A. Sample Implementation of Registration
A.1. Overall summary
In the Registration phase, the objective is to generate a shared
secret that will be used in encryption and decryption during the Data
Transfer phase. How this is to be done is left to the
implementation.
A.2. High level flow
The following steps describe the protocol flow:
1. Client initiates a request to the Server. The request contains a
list of available ciphersuites for KEM, KDF, and AEAD.
2. Server responds to the Client with one of the available
ciphersuites and shares its pkX.
3. Client generates a secret and its encapsulation. The Client
sends the encapsulation and a salt to the Server. The salt is
required during KDF in the Data Transfer phase.
4. Server generates the secret with the help of the encapsulation
and responds with a status message.
Appendix B. Change Log
Note to RFC Editor: if this document does not obsolete an existing
RFC, please remove this appendix before publication as an RFC.
Appendix C. Open Issues
Note to RFC Editor: please remove this appendix before publication as
an RFC.
Authors' Addresses
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Nalini Elkins
Inside Products, Inc.
United States
Email: nalini.elkins@insidethestack.com
Michael Ackermann
BCBS Michigan
United States
Email: mackermann@bcbsm.com
Ameya Deshpande
NITK Surathkal/Google
India
Email: ameyanrd@gmail.com
Tommaso Pecorella
University of Florence
Italy
Email: tommaso.pecorella@unifi.it
Adnan Rashid
Politecnico di Bari
Italy
Email: adnan.rashid@poliba.it
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