Secure Neighbor Discovery Working J. Arkko
Group Ericsson
Internet-Draft J. Kempf
Expires: April 16, 2004 DoCoMo Communications Labs USA
B. Sommerfeld
Sun Microsystems
B. Zill
Microsoft
P. Nikander
Ericsson
October 17, 2003
SEcure Neighbor Discovery (SEND)
draft-ietf-send-ndopt-00
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on April 16, 2004.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
IPv6 nodes use the Neighbor Discovery Protocol (NDP) to discover
other nodes on the link, to determine each the link-layer addresses
of the nodes on the link, to find routers, and to maintain
reachability information about the paths to active neighbors. If not
secured, NDP is vulnerable to various attacks. This document
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specifies security mechanisms for NDP. Unlike to the original NDP
specifications, these mechanisms do not make use of IPsec.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Neighbor and Router Discovery Overview . . . . . . . . . . 7
4. Secure Neighbor Discovery Overview . . . . . . . . . . . . 11
5. Neighbor Discovery Options . . . . . . . . . . . . . . . . 12
5.1 Ordering of the new options . . . . . . . . . . . . . . . 12
5.2 CGA Option . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2.1 Processing Rules for Senders . . . . . . . . . . . . . . . 14
5.2.2 Processing Rules for Receivers . . . . . . . . . . . . . . 15
5.2.3 Configuration . . . . . . . . . . . . . . . . . . . . . . 15
5.3 Signature Option . . . . . . . . . . . . . . . . . . . . . 15
5.3.1 Processing Rules for Senders . . . . . . . . . . . . . . . 18
5.3.2 Processing Rules for Receivers . . . . . . . . . . . . . . 18
5.3.3 Configuration . . . . . . . . . . . . . . . . . . . . . . 19
5.4 Timestamp and Nonce options . . . . . . . . . . . . . . . 20
5.4.1 Timestamp Option . . . . . . . . . . . . . . . . . . . . . 20
5.4.2 Nonce Option . . . . . . . . . . . . . . . . . . . . . . . 21
5.4.3 Processing rules for senders . . . . . . . . . . . . . . . 22
5.4.4 Processing rules for receivers . . . . . . . . . . . . . . 22
5.5 Proxy Neighbor Discovery . . . . . . . . . . . . . . . . . 24
6. Authorization Delegation Discovery . . . . . . . . . . . . 25
6.1 Delegation Chain Solicitation Message Format . . . . . . . 25
6.2 Delegation Chain Advertisement Message Format . . . . . . 27
6.3 Trust Anchor Option . . . . . . . . . . . . . . . . . . . 29
6.4 Certificate Option . . . . . . . . . . . . . . . . . . . . 30
6.5 Router Authorization Certificate Format . . . . . . . . . 31
6.5.1 Router Authorization Certificate Profile . . . . . . . . . 31
6.6 Processing Rules for Routers . . . . . . . . . . . . . . . 32
6.7 Processing Rules for Hosts . . . . . . . . . . . . . . . . 34
7. Securing Neighbor Discovery with SEND . . . . . . . . . . 37
7.1 Neighbor Solicitation Messages . . . . . . . . . . . . . . 37
7.1.1 Sending Secure Neighbor Solicitations . . . . . . . . . . 37
7.1.2 Receiving Secure Neighbor Solicitations . . . . . . . . . 37
7.2 Neighbor Advertisement Messages . . . . . . . . . . . . . 37
7.2.1 Sending Secure Neighbor Advertisements . . . . . . . . . . 37
7.2.2 Receiving Secure Neighbor Advertisements . . . . . . . . . 38
7.3 Other Requirements . . . . . . . . . . . . . . . . . . . . 38
8. Securing Router Discovery with SEND . . . . . . . . . . . 40
8.1 Router Solicitation Messages . . . . . . . . . . . . . . . 40
8.1.1 Sending Secure Router Solicitations . . . . . . . . . . . 40
8.1.2 Receiving Secure Router Solicitations . . . . . . . . . . 40
8.2 Router Advertisement Messages . . . . . . . . . . . . . . 41
8.2.1 Sending Secure Router Advertisements . . . . . . . . . . . 41
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8.2.2 Receiving Secure Router Advertisements . . . . . . . . . . 41
8.3 Redirect Messages . . . . . . . . . . . . . . . . . . . . 41
8.3.1 Sending Redirects . . . . . . . . . . . . . . . . . . . . 41
8.3.2 Receiving Redirects . . . . . . . . . . . . . . . . . . . 42
8.4 Other Requirements . . . . . . . . . . . . . . . . . . . . 42
9. Co-Existence of SEND and non-SEND nodes . . . . . . . . . 43
10. Performance Considerations . . . . . . . . . . . . . . . . 45
11. Security Considerations . . . . . . . . . . . . . . . . . 46
11.1 Threats to the Local Link Not Covered by SEND . . . . . . 46
11.2 How SEND Counters Threats to Neighbor Discovery . . . . . 47
11.2.1 Neighbor Solicitation/Advertisement Spoofing . . . . . . . 47
11.2.2 Neighbor Unreachability Detection Failure . . . . . . . . 48
11.2.3 Duplicate Address Detection DoS Attack . . . . . . . . . . 48
11.2.4 Router Solicitation and Advertisement Attacks . . . . . . 49
11.2.5 Replay Attacks . . . . . . . . . . . . . . . . . . . . . . 49
11.2.6 Neighbor Discovery DoS Attack . . . . . . . . . . . . . . 49
11.3 Attacks against SEND Itself . . . . . . . . . . . . . . . 50
12. IANA Considerations . . . . . . . . . . . . . . . . . . . 51
Normative References . . . . . . . . . . . . . . . . . . . 52
Informative References . . . . . . . . . . . . . . . . . . 54
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 55
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . 57
B. IPR Considerations . . . . . . . . . . . . . . . . . . . . 58
C. Cache Management . . . . . . . . . . . . . . . . . . . . . 59
D. Comparison to AH-Based Approach . . . . . . . . . . . . . 60
Intellectual Property and Copyright Statements . . . . . . 63
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1. Introduction
IPv6 defines the Neighbor Discovery Protocol (NDP) in RFC 2461 [6].
Nodes on the same link use NDP to discover each other's presence, to
determine each other's link-layer addresses, to find routers, and to
maintain reachability information about the paths to active
neighbors. NDP is used both by hosts and routers. Its functions
include Neighbor Discovery (ND), Router Discovery (RD), Address
Autoconfiguration, Address Resolution, Neighbor Unreachability
Detection (NUD), Duplicate Address Detection (DAD), and Redirection.
RFC 2461 called for the use of IPsec for protecting the NDP messages.
However, it does not specify detailed instructions for using IPsec to
secure NDP. It turns out that in this particular application, IPsec
can only be used with a manual configuration of security
associations, due to chicken-and-egg problems in using IKE [22] [19].
Furthermore, the number of such manually configured security
associations needed for protecting NDP can be very large [23], making
that approach impractical for most purposes.
This document is organized as follows. Section 4 describes the
overall approach to securing NDP. This approach involves the use of
new NDP options to carry public-key based signatures. A
zero-configuration mechanism is used for showing address ownership on
individual nodes; routers are certified by a trust anchor [11]. The
formats, procedures, and cryptographic mechanisms for the
zero-configuration mechanism are described in a related specification
[26].
Section 6 describes the mechanism for distributing certificate chains
to establish an authorization delegation chain to a common trust
anchor. The required new NDP options are discussed in Section 5.
Section 7 and Section 8 show how to apply these components to
securing Neighbor and Router Discovery.
Finally, Section 9 discusses the co-existence of secure and
non-secure Neighbor Discovery on the same link, Section 10 discusses
performance considerations, and Section 11 discusses security
considerations for Secure Neighbor Discovery.
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2. Terms
Authorization Delegation Discovery (ADD)
A process through which SEND nodes can acquire a certificate chain
from a peer node to a trust anchor.
Cryptographically Generated Addresses (CGAs)
A technique [26] [30] where the IPv6 address of a node is
cryptographically generated using a one-way hash function from the
node's public key and some other parameters.
Duplicate Address Detection (DAD)
A mechanism defined in RFC 2462 [7] that assures that two IPv6
nodes on the same link are not using the same addresses.
Internet Control Message Protocol version 6 (ICMPv6)
The IPv6 control signaling protocol. Neighbor Discovery is a part
of ICMPv6.
Neighbor Discovery Protocol (NDP)
The IPv6 Neighbor Discovery Protocol [6].
Neighbor Discovery (ND)
The Neighbor Discovery function of the Neighbor Discovery Protocol
(NDP). NDP contains also other functions but ND.
Neighbor Unreachability Detection (NUD)
This mechanism defined in RFC 2461 [6] is used for tracking the
reachability of neighbors.
Nonce
A random number generated by a node and used exactly once, and
never again. In SEND, nonces are used to ensure that a particular
advertisement is linked to the solicitation that triggered it.
Router Authorization Certificate
An X.509v3 [11] PKC certificate using the profile specified in
Section 6.5.1.
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SEND node
An IPv6 node that implements this specification.
non-SEND node
An IPv6 node that does not implement this specification but uses
the legacy RFC 2461 and RFC 2462 mechanisms.
Router Discovery (RD)
The Router Discovery function of the Neighbor Discovery Protocol
(NDP).
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3. Neighbor and Router Discovery Overview
IPv6 Neighbor and Router Discovery have several functions. Many of
these functions are overloaded on a few central message types, such
as the ICMPv6 Neighbor Discovery message. In this section we review
some of these tasks and their effects in order to understand better
how the messages should be treated. This section is not normative,
and if this section and the original Neighbor Discovery RFCs are in
conflict, the original RFCs take precedence.
In IPv6, many of the tasks traditionally preformed at lower the
layers, such as ARP, have been moved to the IP layer. As a
consequence, a set of unified mechanisms can be applied across link
layers, any introduced security mechanisms or other extensions can be
adopted more easily, and a clear separation of the roles between the
IP and link layer has been achieved.
The main functions of IPv6 Neighbor Discovery are the following.
o Neighbor Unreachability Detection (NUD) is used for tracking the
reachability of neighboring nodes, both hosts and routers. NUD is
defined in Section 7.3 of RFC 2461 [6]. NUD is
security-sensitive, because an attacker could falsely claim that
reachability exists when it in fact does not.
o Duplicate Address Detection (DAD) is used for preventing address
collisions [7]. A node that intends to assign a new address to
one of its interfaces first runs the DAD procedure to verify that
there is no other node using the same address. Since the rules
forbid the use of an address until it has been found unique, no
higher layer traffic is possible until this procedure has been
completed. Thus, preventing attacks against DAD can help ensure
the availability of communications for the node in question.
o Address Resolution is similar to IPv4 ARP [18]. The Address
Resolution function resolves a node's IPv6 address to the
corresponding link-layer address for nodes on the link. Address
Resolution is defined in Section 7.2 of RFC 2461 [6], and it is
used for hosts and routers alike. Again, no higher level traffic
can proceed until the sender knows the hardware address of the
destination node or the next hop router. Note that like its
predecessor in ARP, IPv6 Neighbor Discovery does not check the
source link layer address against the information learned through
Address Resolution. This allows for an easier addition of network
elements such as bridges and proxies, and eases the stack
implementation requirements as less information needs to be passed
from layer to layer.
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o Address Autoconfiguration is used for automatically assigning
addresses to a host [7]. This allows hosts to operate without
explicit configuration related to IP connectivity. The Address
Autoconfiguration mechanism defined in [7] is stateless. To create
IP addresses, the hosts use any prefix information delivered to
them during Router Discovery, and then test the newly formed
addresses for uniqueness using the DAD procedure. A stateful
mechanism, DHCPv6 [24], provides additional Autoconfiguration
features. Router and Prefix Discovery and Duplicate Address
Detection have an effect on the Address Autoconfiguration tasks.
o The Redirect function is used for automatically redirecting hosts
to an alternate router. Redirect is specified in Section 8 of RFC
2461 [6]. It is similar to the ICMPv4 Redirect function [17].
o The Router Discovery function allows IPv6 hosts to discover the
local routers on an attached link. Router Discovery is described
in Section 6 of RFC 2461 [6]. The main purpose of Router
Discovery is to find neighboring routers that are willing to
forward packets on behalf of hosts. Prefix discovery involves
determining which destinations are directly on a link; this
information is necessary in order to know whether a packet should
be sent to a router or to the destination node directly.
Typically, address autoconfiguration and other tasks can not
proceed until suitable routers and prefixes have been found.
The Neighbor Discovery messages follow the ICMPv6 message format.
They have ICMPv6 types from 133 to 137. The IPv6 Next Header value
for ICMPv6 is 58. The actual Neighbor Discovery message includes an
NDP message header, consisting of an ICMPv6 header and ND
message-specific data, and zero or more NDP options.
<------------NDP Message---------------->
*-------------------------------------------------------------*
| IPv6 Header | ICMPv6 | ND message- | ND Message |
| Next Header = 58 | Header | specific | Options |
| (ICMPv6) | | data | |
*-------------------------------------------------------------*
<--NDP Message header-->
The NDP message options are formatted in the Type-Length-Value
format.
All IPv6 NDP functions are realized using the following ICMPv6
messages:
ICMPv6 Type Message
------------------------------------
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133 Router Solicitation (RS)
134 Router Advertisement (RA)
135 Neighbor Solicitation (NS)
136 Neighbor Advertisement (NA)
137 Redirect
The various functions are realized using these messages as follows:
o Router Discovery uses the RS and RA messages.
o Duplicate Address Detection uses the NS and NA messages.
o Address Autoconfiguration uses the NS, NA, RS, and RA messages.
o Address Resolution uses the NS and NA messages.
o Neighbor Unreachability Detection uses the NS and NA messages.
o Redirect uses the Redirect message.
The NDP messages are always meant to be used within a link, and never
intended to leak outside of it. The destination and source addresses
used in these messages are as follows:
o Neighbor Solicitation: The destination address is either the
Solicited-Node multicast address, a unicast address, or an anycast
address. The source address is either the unspecified address (in
DAD) or a unicast address assigned to the sending interface. In a
typical case, the source address is equal to the source address of
the outgoing packet, locally triggering the need to send the
solicitation.
o Neighbor Advertisement: The destination address is either a
unicast address or the link-scoped All-Nodes multicast address
[12]. The source address is a unicast address assigned to the
sending interface.
o Router Solicitation: The destination address is typically the
All-Routers multicast address [12]. The source address is either
the unspecified address or a unicast address assigned to the
sending interface. An unspecified source address does not have
any special semantics; it is just an optimization for startup.
o Router Advertisement: The destination address can be either a
unicast or the link-scoped All-Nodes multicast address [12]. The
source address is a link-local address assigned to the sending
interface.
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o Redirect: This message is always sent to the source address of the
packet that triggered the Redirect. Hosts verify that the IP
source address of the Redirect is the same as the current
first-hop router for the specified ICMP Destination Address.
Rules in [12] dictate that anycast, or multicast addresses may not
be used as source addresses. If the source address is an
unspecified address, it is impossible to send a Redirect, since
the unspecified address is forbidden as the destination address.
Therefore, the destination address must always be a unicast
address.
The source address is a link-local address assigned to the sending
interface.
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4. Secure Neighbor Discovery Overview
To secure the various functions, a set of new Neighbor Discovery
options introduced. They are used in to protect Neighbor and Router
Discovery messages. This specification introduces these options, an
authorization delegation discovery process, an address ownership
proof mechanism, and requirements for the use of these components for
Neighbor Discovery.
The components of the solution specified in this document are as
follows:
o Certificate chains, anchored on trusted parties, are expected to
certify the authority of routers. A host and a router must have
at least one common trust anchor before the host can adopt the
router as its default router. Delegation Chain Solicitation and
Advertisement messages are used to discover a certificate chain to
the trust anchor without requiring the actual Router Discovery
messages to carry lengthy certificate chains.
o Cryptographically Generated Addresses are used to assure that the
sender of a Neighbor or Router Advertisement is the "owner" of the
claimed address. A public-private key pair needs to be generated
by all nodes before they can claim an address. A new Neighbor
Discovery option, the CGA option, is used to carry the public key
and associated parameters.
This specification also allows one to use non-CGA addresses and to
use certificates to authorized their use. However, the details of
such use have been left for future work.
o A new Neighbor Discovery option, the Signature option, is used to
protect all messages relating to Neighbor and Router discovery.
Public key signatures are used to protect the integrity of the
messages and to authenticate the identity of their sender. The
authority of a public key is established either with the
authorization delegation process, using certificates, or through
the address ownership proof mechanism, using CGAs, or both,
depending on configuration and the type of the message protected.
o In order to prevent replay attacks, two new Neighbor Discovery
options, Timestamp and Nonce, are used. Given that Neighbor and
Router Discovery messages are in some cases sent to multicast
addresses, the Timestamp option offers replay protection without
any previously established state or sequence numbers. When the
messages are used in solicitation - advertisement pairs, they
protected using the Nonce option.
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5. Neighbor Discovery Options
The following new NDP options and mechanisms are REQUIRED to be
implemented by all SEND nodes:
o The CGA option MAY be present in all Neighbor Discovery messages,
and SHOULD be present in most cases.
o The Signature option is REQUIRED in all Neighbor Discovery
messages.
o The Nonce option is REQUIRED in all Neighbor Discovery
solicitations, and in all solicited advertisements.
o The Timestamp option is REQUIRED in all Neighbor Discovery
advertisements and Redirects.
o Proxy Neighbor Discovery is not supported by this specification;
it is planned to be specified in a future document.
5.1 Ordering of the new options
The ordering of the new options MUST obey the following rules:
The CGA option MUST appear before the Signature option.
The Nonce option SHOULD appear before the Timestamp option.
The Signature option MUST NOT be be followed CGA, Nonce, or
Timestamp options.
It is RECOMMENDED that the options appear in the following order:
CGA, Nonce, Timestamp, Signature.
5.2 CGA Option
The CGA option allows the verification of the sender's CGA. The
format of the CGA option is described as follows.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Modifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Collision Cnt | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| |
. .
. Key Information .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The meaning of the fields is described as follows.
Type
TBD <To be assigned by IANA> for CGA.
Length
The length of the option, in units of 8 octets.
Modifier
A random number used in CGA generation. Its semantics are defined
in [26].
Collision Cnt
An 8-bit collision count, which can get values 0, 1 and 2. Its
semantics are defined in [26].
Reserved
A 24-bit field reserved for future use. The value MUST be
initialized to zero by the sender, and MUST be ignored by the
receiver.
Key Information
A variable length field containing the public key of the sender,
represented as an ASN.1 type SubjectPublicKeyInfo [11], encoded as
described in Section 4 of [26].
This specification requires that if both the CGA option and the
Signature option are present, then the publicKey field in the
former option MUST be the public key referred by the Key Hash
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field in the latter option. Packets received with two different
keys MUST be silently discarded. Note that a future extension may
provide a mechanism which allows the owner of an address and the
signer to be different parties.
The length of the Key Information field is determined by the ASN.1
encoding.
Padding
A variable length field making the option length a multiple of 8.
It begins after the ASN.1 encoding of the previous field has ends,
and continues to the end of the option, as specified by the Length
field.
5.2.1 Processing Rules for Senders
A node sending a message using the CGA option MUST construct the
message as follows.
The Modifier, Collision Cnt, and Key Information fields in the CGA
option are filled in according to the rules presented above and in
[26]. The used public key is taken from configuration; typically
from a data structure associated with the source address.
An address MUST be constructed as specified in Section 4 of [26]. In
the typical case, the address is constructed long before it is used.
Depending on the type of the message, this address appears in
different places:
Redirect
The address MUST be the source address of the message.
Neighbor Solicitation
The address MUST be the Target Address for solicitations sent for
the purpose of Duplicate Address Detection, and the source address
of the message otherwise.
Neighbor Advertisement
The address MUST be the source address of the message.
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Router Solicitation
The address MUST be the source address of the message, unless the
source address is the unspecified address.
Router Advertisement
The address MUST be the source address of the message.
5.2.2 Processing Rules for Receivers
A message containing a CGA option MUST be checked as follows:
If the interface has been configued to use CGA, it is REQUIRED
that the receiving node verifies the source address of the packet
using the algorithm described in Section 5 of [26]. The inputs
for the algorithm are the contents of the Modifier, Collision Cnt,
and the Key Information fields, the claimed address in the packet
(as discussed in the previous section), and the minimum acceptable
Sec value. If the CGA verification is successful, the recipient
proceeds with the cryptographically more time consuming check of
the signature.
Note that a receiver which does not support CGA or has not specified
its use for a given interface can still verify packets using trust
anchors, even if CGA had been used on a packet. In such a case, the
CGA property of the address is simply left unverified.
5.2.3 Configuration
All nodes that support the verification of the CGA option MUST record
the following configuration information:
minbits
The minimum acceptable key length for the public keys used in the
generation of the CGA address. The default SHOULD be 1024 bits.
Implementations MAY also set an upper limit in order to limit the
amount of computation they need to perform when verifying packets
that use these security associations. Any implementation should
follow prudent cryptographic practise in determining the
appropriate key lengths.
5.3 Signature Option
The Signature option allows public-key based signatures to be
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attached to NDP messages. Both trust anchor authentication and CGAs
can be used. The format of the Signature option is described in the
following:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Pad Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Key Hash |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Digital Signature .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The meaning of the fields is described below:
Type
TBD <To be assigned by IANA> for Signature.
Length
The length of the option, in units of 8 octets.
Pad Length
An 8-bit integer field, giving the length of the Pad field in
units of an octet.
Reserved
An an 8-bit field reserved for future use. The value MUST be
initialized to zero by the sender, and MUST be ignored by the
receiver.
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Key Hash
A 128-bit field contains the most significant (leftmost) 128-bits
of a SHA1 hash of the public key used for the constructing the
signature. The SHA1 is taken over the presentation used in the
Key Information field in the CGA option. Its purpose is to
associate the signature to a particular key known by the receiver.
Such a key can be either stored in the certificate cache of the
receiver, or be received in the CGA option in the same message.
Digital Signature
A variable length field contains the signature constructed using
the sender's private key, over the the following sequence of
octets:
1. The 128-bit CGA Type Tag [26] value for SEND, 0xXXXX XXXX XXXX
XXXX XXXX XXXX XXXX XXXX (To be generated randomly).
2. The 128-bit Source Address field from the IP header.
3. The 128-bit Destination Address field from the IP header.
4. The 32-bit ICMP header, i.e., the Type, Code, and Checksum
fields.
5. The Neighbor Discovery message header, i.e., the Reserved
field in the Router Solicitation message, the Cur Hop Limit,
M, O, Reserved, Router Lifetime, Reachable Time, and Retrans
Timer fields in the Router Advertisement message, Reserved and
Target Address fields in the Neighbor Solicitation message, R,
S, O, Reserved, and Target Address fields in the Neighbor
Advertisement message, and Reserved, Target Address, and
Destination Address fields in the Redirect message.
6. All NDP options preceding the Signature option.
The signature is constructed using the RSA algorithm and MUST be
encoded as private key encryption in PKCS#1 format [15]. The
signature value is computed with the RSASSA-PKCS1-v2_1 algorithm
and SHA-1 hash as defined in [15].
This field starts after the Key Hash field. The length of the
Digital Signature field is determined by the length of the
Signature option minus the length of the other fields (including
the variable length Pad field).
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This variable length field contains padding, as many bytes as is
given by the Pad Length Field.
5.3.1 Processing Rules for Senders
A node sending a message using the Signature option MUST construct
the message as follows:
o The message is constructed in its entirety.
o The Signature option is added as the last option in the message.
o For the purpose of constructing a signature, the following data
items are concatenated:
* The 128-bit CGA Type Tag.
* The source address of the message.
* The destination address of the message.
* The contents of the message, starting from the ICMPv6 header,
up to but excluding the Signature option.
o The message, in the form defined above, is signed using the
configured private key, and the resulting PKCS#1 signature is put
to the Digital Signature field.
5.3.2 Processing Rules for Receivers
A message containing a Signature option MUST be checked as follows:
o The Signature option MUST appear as the last option.
o The Key Hash field MUST indicate the use of a known public key,
either one learned from a preceeding CGA option, or one known by
other means.
o TheDigital Signature field MUST have correct encoding, and do not
exceed the length of the Signature option.
o The Digital Signature verification MUST show that the signature
has been calculated as specified in the previous section.
o If the use of a trust anchor has been configured, a valid
authorization delegation chain MUST be known between the
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receiver's trust anchor and the sender's public key.
Note that the receiver may verify just the CGA property of a
packet, even if, in addition to CGA, the sender has used a trust
anchor.
Messages that do not pass all the above tests MUST be silently
discarded. The receiver MAY silently drop packets also otherwise,
e.g., as a response to an apparent CPU exhausting DoS attack.
5.3.3 Configuration
All nodes that support the reception of the Signature options MUST
record the following configuration information for each separate
Neighbor Discovery Protocol message type:
authorization method
This parameter determines the method through which the authority
of the sender is determined. It can have four values:
trust anchor
The authority of the sender is verified as described in Section
6.5. The sender may claim additional authorization through the
use of CGAs, but that is neither required nor verified.
CGA
The CGA property of the sender's address is verified as
described in [26]. The sender may claim additional authority
through a trust anchor, but that is neither required nor
verified.
trust anchor and CGA
Both the trust anchor and the CGA verification is required.
trust anchor or CGA
Either the trust anchor or the CGA verification is required.
anchor
The public keys of the allowed trust anchor(s), if authorization
method is not set to CGA.
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minSec
The minimum acceptable Sec value, if CGA verification is required
(see Section 2 in [26]). This parameter is intended to facilitate
future extensions and experimental work. Currently, the minSec
value SHOULD always be set to zero.
All nodes that support the sending of Signature options MUST record
the following configuration information:
keypair
A public-private key pair. If authorization delegation is in use,
there must exist a delegation chain from a trust anchor to this
key pair.
CGA flag
A flag that indicates whether CGA is used or is not used. This
flag may be per interface or per node.
CGA parameters
Optionally any information required to construct CGAs, including
the used Sec and Modifier values, and the CGA address itself.
5.4 Timestamp and Nonce options
5.4.1 Timestamp Option
The purpose of the Timestamp option is to ensure that unsolicited
advertisements and redirects have not been replayed. The format of
the Timestamp option is described in the following:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Timestamp +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where the fields are as follows:
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Type
TBD <To be assigned by IANA> for Timestamp.
Length
The length of the option, in units of 8 octets, i.e., 2.
Reserved
A 48-bit field reserved for future use. The value MUST be
initialized to zero by the sender, and MUST be ignored by the
receiver.
Timestamp
A 64-bit unsigned integer field containing a timestamp. The value
indicates the number of seconds since January 1,, 1970 00:00 UTC,
using a fixed point format. In this format the integer number of
seconds is contained in the first 48 bits of the field, and the
remaining 16 bits indicate the number of 1/64K fractions of a
second.
5.4.2 Nonce Option
The purpose of the Nonce option is to ensure that an advertisement is
a fresh response to a solicitation sent earlier by the receiving same
node. The format of the Nonce option is as described in the
following:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Nonce ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
. .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where the fields are as follows:
Type
TBD <To be assigned by IANA> for Nonce.
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Length
The length of the option, in units of 8 octets.
Nonce
A field containing a random number selected by the sender of the
solicitation message. The length of the random number MUST be at
least 6 bytes.
5.4.3 Processing rules for senders
All solicitation messages MUST include a Nonce. All solicited-for
announcements MUST include a Nonce, copying the nonce value from the
received solicitation. When sending a solication, the sender MUST
store the nonce internally so that it can recognize any replies
containing that particular nonce.
All NDP messages MUST include a Timestamp. Senders SHOULD set the
Timestamp field to the current time, according to their real time
clock.
If a message has both Nonce and Timestamp options, the Nonce option
SHOULD precede the Timestamp option in order. The receiver MUST be
prepared to receive them in any order, as per RFC 2461 [6] Section 9.
5.4.4 Processing rules for receivers
The processing of the Nonce and Timestamp options depends on whether
a packet is a solicited-for advertisement or not. A system may
implement the distinction in various means. Section 5.4.4.1 defines
the processing rules for solicited-for advertisements. Section
5.4.4.2 defines the processing rules for all other messages.
An implementation may utilize some mechanism such as a timestamp
cache to strengthen resistance to replay attacks. When there is a
very large number of nodes on the same link, or when a cache filling
attack is in progress, it is possible that the cache holding the most
recent timestamp per sender becomes full. In this case the node MUST
remove some entries from the cache or refuse some new requested
entries. The specific policy as to which entries are preferred over
the others is left as an implementation decision. However, typical
policies may prefer existing entries over new ones, CGAs with a large
Sec value over smaller Sec values, and so on. The issue is briefly
discussed in Appendix C.
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5.4.4.1 Processing solicited-for advertisements
The receiver MUST verify that it has recently send a matching
solicitation, and that the received advertisement does contain a copy
of the Nonce sent in the solicitation.
If the message does not contain a Nonce option, it MAY be considered
as a non-solicited-for announcement, and processed according to
Section 5.4.4.2.
If the message does contain a Nonce option, but the Nonce value is
not recognized, the message MUST be silently dropped.
If the message is accepted, the receiver SHOULD store the receive
time of the message and the time stamp time in the message, as
specified in Section 5.4.4.2
5.4.4.2 Processing all other messages
Receivers SHOULD be configured with an allowed timestamp Delta value
and an allowed clock drift parameter. The recommended default value
for the allowed Delta is 3,600 seconds (1 hour) and for clock dritf
1% (0.01).
To facilitate timestamp checking, each node SHOULD store the
following information per each peer:
The receive time of the last received, acepted SEND message. This
is called RDlast.
The time stamp in the last received, accepted SEND message. This
is called TSlast.
Receivers SHOULD then check the Timestamp field as follows:
o When a message is received from a new peer, i.e., one that is not
stored in the cache, the received timestamp, TSnew, is checked and
the packet is accepted if the timestamp is recent enough with
respect to the receival time of the packet, RDnew:
-Delta < (RDnew - TSnew) < +Delta
The RDnew and TSnew values SHOULD be stored into the cache as
RDlast and TSlast.
o If the timestamp is NOT within the boundaries but the message is a
Neighbor Solicitation message that should be responded to by the
receiver, the receiver MAY respond to the message. However, if it
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does respond to the message, it MUST NOT create a neighbor cache
entry. This allows nodes that have large difference in their
clocks to still communicate with each other, by exchanging NS/NA
pairs.
o When a message is received from a known peer, i.e., one that
already has an entry in the cache, the time stamp is checked
against the previously received SEND message:
TSnew > TSlast + (RDnew - RDlast) x (1 - drift)
o If TSnew < TSlast, which is possible if packets arrive rapidly and
out of order, TSlast MUST NOT be updated, i.e., the stored TSlast
for a given node MUST NOT ever decrease. Otherwise TSlast SHOULD
be updated. Independent on whether TSlast is updated or not,
RDlast is updated in any case.
5.5 Proxy Neighbor Discovery
The Target Address in Neighbor Advertisement is required to be equal
to the source address of the packet, except in the case of proxy
Neighbor Discovery. Proxy Neighbor Discovery is not supported by
this specification; it is planned to be specified in a future
document.
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6. Authorization Delegation Discovery
Several protocols, including the IPv6 Neighbor Discovery Protocol,
allow a node to automatically configure itself based on information
it learns shortly after connecting to a new link. It is particularly
easy to configure "rogue" routers on an unsecured link, and it is
particularly difficult for a node to distinguish between valid and
invalid sources of information, when the node needs this information
before being able to communicate with nodes outside of the link.
Since the newly-connected node cannot communicate off-link, it can
not be responsible for searching information to help validating the
router(s); however, given a chain of appropriately signed
certificates, it can check someone else's search results and conclude
that a particular message comes from an authorized source. In the
typical case, a router, which is already connected to beyond the
link, can (if necessary) communicate with off-link nodes and
construct such a certificate chain.
The Secure Neighbor Discovery Protocol introduces two new ICMPv6
messages that are used between hosts and routers to allow the host to
learn a certificate chain with the assistance of the router. Where
hosts themselves are certified by a trust anchor, these messages MAY
also optionally be used between hosts to acquire the peer's
certificate chain. However, the details of such usage are left for
future specification.
The Delegation Chain Solicitation (DCS) message is sent by a host
when it wishes to request a certificate chain between a router and
the one of the host's trust anchors. The Delegation Chain
Advertisement (DCA) message is sent as an answer to the DCS message.
It MAY be periodically sent to the link-scoped All-Nodes multicast
address. These messages are separate from the rest of Neighbor and
Router Discovery, in order to reduce the effect of the potentially
voluminous certificate chain information on other messages.
The Authorization Delegation Discovery (ADD) process does not exclude
other forms of discovering certificate chains. For instance, during
fast movements mobile nodes may learn information - including the
certificate chains - of the next router from a previous router.
6.1 Delegation Chain Solicitation Message Format
Hosts send Delegation Chain Solicitations in order to prompt routers
to generate Delegation Chain Advertisements quickly.
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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
IP Fields:
Source Address
An IP address assigned to the sending interface, or the
unspecified address if no address is assigned to the sending
interface.
Destination Address
Typically the All-Routers multicast address, the Solicited-Node
multicast address, or the address of the host's default router.
Hop Limit
255
ICMP Fields:
Type
TBD <To be assigned by IANA> for Delegation Chain Solicitation.
Code
0
Checksum
The ICMP checksum [8].
Identifier
A 16-bit unsigned integer field, acting as an identifier to
help matching advertisements to solicitations. The Identifier
field MUST NOT be zero, and its value SHOULD be randomly
generated. (This randomness does not need to be
cryptographically hard, though. Its purpose is to avoid
collisions.)
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Reserved
An unused field. It MUST be initialized to zero by the sender
and MUST be ignored by the receiver.
Valid Options:
Trust Anchor
One or more trust anchors that the client is willing to accept.
The first (or only) Trust Anchor option MUST contain a DER
Encoded X.501 Name; see Section 6.3. If there are more than
one Trust Anchor options, the options past the first one may
contain any types of Trust Anchors.
Future versions of this protocol may define new option types.
Receivers MUST silently ignore any options they do not recognize
and continue processing the message.
6.2 Delegation Chain Advertisement Message Format
Routers send out Delegation Chain Advertisement messages
periodically, or in response to a Delegation Chain Solicitation.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier | Component |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
IP Fields:
Source Address
MUST be a unicast address assigned to the interface from which
this message is sent.
Destination Address
Either the Solicited-Node multicast address of the receiver or
the link-scoped All-Nodes multicast address.
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Hop Limit
255
ICMP Fields:
Type
TBD <To be assigned by IANA> for Delegation Chain
Advertisement.
Code
0
Checksum
The ICMP checksum [8].
Identifier
A 16-bit unsigned integer field, acting as an identifier to
help matching advertisements to solicitations. The Identifier
field MUST be zero for unsolicited advertisements and MUST NOT
be zero for solicited advertisements.
Component
A 16-bit unsigned integer field, used for informing the
receiver which certificate is being sent, and how many are
still left to be sent in the whole chain.
A single advertisement MUST be broken into separately sent
components if there is more than one Certificate option, in
order to avoid excessive fragmentation at the IP layer. Unlike
the fragmentation at the IP layer, individual components of an
advertisement may be stored and used before all the components
have arrived; this makes them slightly more reliable and less
prone to Denial-of-Service attacks.
The first message in a N-component advertisement has the
Component field set to N-1, the second set to N-2, and so on.
Zero indicates that there are no more components coming in this
advertisement.
The components MUST be ordered so that the trust anchor end of
the chain is the one sent first. Each certificate sent after
it can be verified with the previously sent certificates. The
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certificate of the sender comes last.
Reserved
An unused field. It MUST be initialized to zero by the sender
and MUST be ignored by the receiver.
Valid Options:
Certificate
One certificate is provided in each Certificate option, to
establish a (part of a) certificate chain to a trust anchor.
Trust Anchor
Zero or more Trust Anchor options may be included to help
receivers decide which advertisements are useful for them. If
present, these options MUST appear in the first component of a
multi-component advertisement.
Future versions of this protocol may define new option types.
Receivers MUST silently ignore any options they do not recognize
and continue processing the message.
6.3 Trust Anchor Option
The format of the Trust Anchor option is as described in the
following:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Name Type | Pad Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Name ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where the fields are as follows:
Type
TBD <To be assigned by IANA> for Trust Anchor.
Length
The length of the option, (including the Type, Length, Name Type,
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Name Length, and Name fields,) in units of 8 octets.
Name Type
The type of the name included in the Name field. This
specification defines only one legal value for this field:
1 DER Encoded X.501 Name
2 FQDN
Pad Length
The number of padding octets beyond the end of the Name field but
within the length specified by the Length field. Padding octets
MUST be set to zero by senders and ignored by receivers.
Name
When the Name Type field is set to 1, the Name field contains a
DER encoded X.501 certificate Name, represented and encoded
exactly as in the matching X.509v3 trust anchor certificate.
When the Name Type field is set to 2, the Name field contains a
Fully Qualified Domain Name of the trust anchor, for example,
"trustanchor.example.com". The name is stored as a string, in the
"preferred name syntax" DNS format, as specified in RFC 1034 [1]
Section 3.5. Additionally, the restrictions discussed in RFC 3280
[11] Section 4.2.1.7 apply.
All systems MUST implement support the DER Encoded X.501 Name.
Implementations MAY support the FQDN name type.
6.4 Certificate Option
The format of the certificate option is as described in the
following:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Cert Type | Pad Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Certificate ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where the fields are as follows:
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Type
TBD <To be assigned by IANA> for Certificate.
Length
The length of the option, (including the Type, Length, Cert Type,
Pad Length, and Certificate fields,) in units of 8 octets.
Cert Type
The type of the certificate included in the Certificate field.
This specification defines only one legal value for this field:
1 X.509v3 Certificate, as specified below
Pad Length
The number of padding octets beyond the end of the Certificate
field but within the length specified by the Length field. Padding
octets MUST be set to zero by senders and ignored by receivers.
Certificate
When the Cert Type field is set to 1, the Certificate field
contains an X.509v3 certificate [11], as described in Section
6.5.1.
6.5 Router Authorization Certificate Format
The certificate chain of a router terminates in a Router
Authorization Certificate that authorizes a specific IPv6 node to act
as a router. Because authorization chains are not a common practice
in the Internet at the time this specification is being written, the
chain MUST consist of standard Public Key Certificates (PKC, in the
sense of [21]). The certificates chain MUST start from the identity
of a trust anchor that is shared by the host and the router. This
allows the host to anchor trust for the router's public key in the
trust anchor. Note that there MAY be multiple certificates issued by
a single trust anchor.
6.5.1 Router Authorization Certificate Profile
Router Authorization Certificates be X.509v3 certificates, as defined
in RFC 3280 [11], and MUST contain at least one instance of the X.509
extension for IP addresses, as defined in [13]. The parent
certificates in the certificate chain MUST contain one or more X.509
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IP address extensions, back up to the delegating authority (the
Regional Address Registry or IANA) that delegated the original IP
address space block. The certificates for intermediate delegating
authorities MUST contain X.509 IP address extension(s) for
subdelegations. The router's certificate is signed by the delegating
authority for the prefixes the router is authorized to to advertize.
The X.509 IP address extension MUST contain at least one
addressesOrRanges element that contains an addressPrefix element with
an IPv6 address prefix for a prefix the router or the intermediate
entity is authorized to advertize. If the entity is allowed to route
any prefix, the used IPv6 address prefix is the null prefix, 0/0.
The addressFamily element of the containing IPAddrBlocks sequence
element MUST contain the IPv6 AFI (0002), as specified in [13] for
IPv6 prefixes. Instead of an addressPrefix element, the
addressesOrRange element MAY contain an addressRange element for a
range of prefixes, if more than one prefix is authorized. The X.509
IP address extension MAY contain additional IPv6 prefixes, expressed
either as an addressPrefix or an addressRange.
A SEND node receiving a Router Authorization Certificate MUST first
check whether the certificate's signature was generated by the
delegating authority. Then the client MUST check whether all the
addressPrefix or addressRange entries in the router's certificate are
contained within the address ranges in the delegating authority's
certificate, and whether the addressPrefix entries match any
addressPrefix entries in the delegating authority's certificate. If
an addressPrefix or addressRange is not contained within the
delegating authority's prefixes or ranges, the client MAY attept to
take an intersection of the ranges/prefixes, and use that
intersection. If the addressPrefix in the certificate is the null
prefix, 0/0, such an intersection SHOULD be used. (In that case the
intersection is the parent prefix or range.) If the resulting
intersection is empty, the client MUST NOT accept the certificate.
The above check SHOULD be done for all certificates in the chain
received through DCA messages. If any of the checks fail, the client
MUST NOT accept the certificate.
Since it is possible that some PKC certificates used with SEND do not
immediately contain the X.509 IP address extension element, an
implementation MAY contain facilities that allow the prefix and range
checks to be relaxed. However, any such configuration options SHOULD
be off by default. That is, the system SHOULD have a default
configuration that requires rigorious prefix and range checks.
6.6 Processing Rules for Routers
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Routers SHOULD possess a key pair and a certificate from at least one
certificate authority.
A router MUST silently discard any received Delegation Chain
Solicitation messages that do not satisfy all of the following
validity checks:
o The IP Hop Limit field MUST have a value of 255, i.e., the packet
could not possibly have been forwarded by a router.
o If the message includes an IP Authentication Header, the message
authenticates correctly.
o ICMP Checksum is valid.
o ICMP Code is 0.
o ICMP length (derived from the IP length) is 8 or more octets.
o Identifier field is non-zero.
o All included options have a length that is greater than zero.
The contents of the Reserved field, and of any unrecognized options,
MUST be ignored. Future, backward-compatible changes to the protocol
may specify the contents of the Reserved field or add new options;
backward-incompatible changes may use different Code values. The
contents of any defined options that are not specified to be used
with Router Solicitation messages MUST be ignored and the packet
processed in the normal manner. The only defined option that may
appear is the Trust Anchor option. A solicitation that passes the
validity checks is called a "valid solicitation".
Routers MAY send unsolicited Delegation Chain Advertisements for
their configured trust anchor(s). When such advertisements are sent,
their timing MUST follow the rules given for Router Advertisements in
RFC 2461 [6]. The only defined options that may appear are the
Certificate and Trust Anchor options. At least one Certificate option
MUST be present. Router SHOULD also include at least one Trust
Anchor option to indicate the trust anchor on which the Certificate
is based.
In addition to sending periodic, unsolicited advertisements, a router
sends advertisements in response to valid solicitations received on
an advertising interface. If the source address in the solicitation
was the unspecified address, the router MUST send the response to the
link-scoped All-Nodes multicast address. If the source address was a
unicast address, the router MUST send the response to the
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Solicited-Node multicast address corresponding to the source address.
In a solicited-for advertisement, the router SHOULD include suitable
Certificate options so that a delegation chain to the solicited trust
anchor can be established. The anchor is identified by the Trust
Anchor option. If the Trust Anchor option is represented as a DER
Encoded X.501 Name, then the Name must be equal to the Subject field
in the anchor's certificate. If the Trust Anchor option is
represented as an FQDN, the FQDN must be equal to an FQDN in the
subjectAltName field of the anchor's certificate. The router SHOULD
include the Trust Anchor option(s) in the advertisement for which the
delegation chain was found.
If the router is unable to find a chain to the requested anchor, it
SHOULD send an advertisement without any certificates. In this case
the router SHOULD include the Trust Anchor options which were
solicited.
Rate limiting of Delegation Chain Advertisements is performed as
specified for Router Advertisements in RFC 2461 [6].
6.7 Processing Rules for Hosts
Hosts SHOULD possess the public key and trust anchor name of at least
one certificate authority, they SHOULD possess their own key pair,
and they MAY posses a certificate from the above mentioned
certificate authority.
A host MUST silently discard any received Delegation Chain
Advertisement messages that do not satisfy all of the following
validity checks:
o IP Source Address MUST be a unicast address. Note that routers
may use multiple addresses, and therefore this address not
sufficient for the unique identification of routers.
o IP Destination Address MUST be either the link-scoped All-Nodes
multicast address or the Solicited-Node multicast address
corresponding to one of the unicast addresses assigned to the
host.
o The IP Hop Limit field MUST have a value of 255, i.e., the packet
could not possibly have been forwarded by a router.
o If the message includes an IP Authentication Header, the message
authenticates correctly.
o ICMP Checksum is valid.
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o ICMP Code is 0.
o ICMP length (derived from the IP length) is 16 or more octets.
o All included options have a length that is greater than zero.
The contents of the Reserved field, and of any unrecognized options,
MUST be ignored. Future, backward-compatible changes to the protocol
may specify the contents of the Reserved field or add new options;
backward-incompatible changes may use different Code values. The
contents of any defined options that are not specified to be used
with Delegation Chain Advertisement messages MUST be ignored and the
packet processed in the normal manner. The only defined options that
may appear are the Certificate and Trust Anchor options. An
advertisement that passes the validity checks is called a "valid
advertisement".
Hosts SHOULD store certificate chains retrieved in Delegation Chain
Discovery messages if they start from an anchor trusted by the host.
The certificates chains SHOULD be verified, as defined in Section
6.5, before storing them. Routers are required to send the
certificates one by one, starting from the trust anchor end of the
chain. Except for temporary purposes to allow for message loss and
reordering, hosts SHOULD NOT store certificates received in a
Delegation Chain Advertisement unless they contain a certificate
which can be immediately verified either to the trust anchor or to a
certificate which has been verified earlier.
Note that it may be useful to cache this information and implied
verification results for use over multiple attachments to the
network.
When an interface becomes enabled, a host may be unwilling to wait
for the next unsolicited Delegation Chain Advertisement. To obtain
such advertisements quickly, a host MAY transmit up to
MAX_RTR_SOLICITATIONS Delegation Chain Solicitation messages, each
separated by at least RTR_SOLICITATION_INTERVAL seconds. Delegation
Chain Solicitations MAY be sent after any of the following events:
o The interface is initialized at system startup time.
o The interface is reinitialized after a temporary interface failure
or after being temporarily disabled by system management.
o The system changes from being a router to being a host, by having
its IP forwarding capability turned off by system management.
o The host attaches to a link for the first time.
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o A movement has been indicated by lower layers or has been inferred
from changed information in a Router Advertisement.
o The host re-attaches to a link after being detached for some time.
o A Router Advertisement has been received with a public key that is
not stored in the hosts' cache of certificates, or there is no
authorization delegation chain to the host's trust anchor.
Delegation Chain Solicitations SHOULD NOT be sent if the host has a
currently valid certificate chain from a reachable router to a trust
anchor.
When soliciting certificates for a router, a host MUST send
Delegation Chain Solicitations either to the All-Routers multicast
address, if it has not selected a default router yet, or to the
default router's IP address, if it has already been selected.
If two hosts want to establish trust with the DCS and DCA messages,
the DCS message SHOULD be sent to the Solicited-Node multicast
address of the receiver. The advertisements SHOULD be sent as
specified above for routers. However, the exact details are left for
a future specification.
Delegation Chain Solicitations SHOULD be rate limited and timed
similarly with Router Solicitations, as specified in RFC 2461 [6].
When processing possible advertisements sent as responses to a
solicitation, the host MAY prefer to process first those
advertisements with the same Identifier field value as in the
solicitation. This makes Denial-of-Service attacks against the
mechanism harder (see Section 11.3).
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7. Securing Neighbor Discovery with SEND
This section describes how to use the mechanisms from Section 5,
Section 6, and the reference [26] in order to provide security for
Neighbor Discovery.
There is no requirement that nodes use both Secure Neighbor Discovery
(as described in this Section) and Secure Router Discovery (as
described in Section 8. They MAY be used indepedently.
7.1 Neighbor Solicitation Messages
All Neighbor Solicitation messages are protected with SEND.
7.1.1 Sending Secure Neighbor Solicitations
Secure Neighbor Solicitation messages are sent as described in RFC
2461 and 2462, with the additional requirements as listed in the
following:
All Neighbor Solicitation messages sent MUST contain the Nonce,
Timestamp, and Signature options, and MAY contain the CGA option.
The Signature option MUST be constructed with the sender's key
pair, using the configured authorization method(s), and if
applicable, using the trust anchor and/or minSec value as
configured.
7.1.2 Receiving Secure Neighbor Solicitations
Received Neighbor Solicitation messages are processed as described in
RFC 2461 and 2462, with the additional SEND-related requirements as
listed in the following:
Neighbor Solicitation messages received without the Nonce,
Timestamp, or Signature option MUST be silently discarded. The
Signature option MUST be constructed with the expected
authorization method(s), the used key being within the configured
minimum (and maximum) allowable key size, and if applicable, using
an acceptable trust anchor and/or minSec value.
7.2 Neighbor Advertisement Messages
All Neighbor Advertisement messages are protected with SEND.
7.2.1 Sending Secure Neighbor Advertisements
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Secure Neighbor Advertisement messages are sent as described in RFC
2461 and 2462, with the additional requirements as listed in the
following:
All Neighbor Advertisement messages sent MUST be sent with the
Timestamp and Signature options and MAY be sent with the CGA
option. The Signature option MUST be constructed with the sender's
key pair, setting the authorization method and additional
information as configured.
Neighbor Advertisements sent in response to a Neighbor
Solicitation MUST additionally contain a copy of the Nonce option
included in the solicitation.
7.2.2 Receiving Secure Neighbor Advertisements
Received Neighbor Advertisement messages are processed as described
in RFC 2461 and 2462, with the additional SEND-related requirements
as listed in the following:
Any eighbor Advertisement messages received without the Timestamp
or Signature options MUST be silently discarded. The Signature
option MUST be constructed with the expected authorization
method(s), the used key being within the configured minimum (and
maximum) allowable key size, and if applicable, using an
acceptable trust anchor and/or minSec value.
Received Neighbor Advertisements sent to a unicast destination
address without a Nonce option MUST be silently discarded.
7.3 Other Requirements
Upon receiving a message for which the receiver has no certificate
chain to a trust anchor, the receiver MAY use Authorization
Delegation Discovery to learn the certificate chain of the peer.
Nodes that use stateless address autoconfiguration, SHOULD generate a
new CGA as specified in Section 4 of [26] for each new
autoconfiguration run. The nodes MAY continue to use the same public
key and modifier, and start the process from Step 4.
This specification does not address the protection of Neighbor
Discovery packets for nodes that are configured with a static address
(e.g., PREFIX::1). Future certificate chain based authorization
specifications are needed for such nodes.
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It is outside the scope of this specification to describe the use of
trust anchor authorization between nodes with dynamically changing
addresses. Such dynamically changing addresses may be the result of
stateful or stateless address autoconfiguration, or through the use
of RFC 3041 [9] addresses. If the CGA method is not used, nodes
would be required to exchange certificate chains that terminate in a
certificate authorizing a node to use an IP address having a
particular interface identifier. This specification does not specify
the format of such certificates, since there are currently a few
cases where such certificates are required by the link layer and it
is up to the link layer to provide certification for the interface
identifier. This may be the subject of a future specification. It
is also outside the scope of this specification to describe how
stateful address autoconfiguration works with the CGA method.
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8. Securing Router Discovery with SEND
This section describes how to use the mechanisms from Section 5,
Section 6, and the reference [26] in order to provide security for
Router Discovery.
8.1 Router Solicitation Messages
All Router Solicitation messages are protected with SEND.
8.1.1 Sending Secure Router Solicitations
Secure Router Solicitation messages are sent as described in RFC
2461, with the additional requirements as listed in the following:
Router Solicitation messages sent with an unspecified source
address MUST have the Nonce and Timestamp options.
Other Router Solicitations MUST have the Nonce, Timestamp, and
Signature options. The Signature option MUST be configured with
the sender's key pair, setting the authorization method and
additional information as is configured.
8.1.2 Receiving Secure Router Solicitations
Received Router Solicitation messages are processed as described in
RFC 2461, with the additional SEND-related requirements as listed in
the following:
Router Solicitation message sent with an unspecified source
address and without the Nonce or Timestamp options MUST be
silently discarded.
Router Solicitation messages received with another type of source
address but without the Nonce, Timestamp, or Signature options
MUST be silently discarded.
The Signature option MUST be constructed with the configured
authorization method(s), the used key being within the configured
minimum (and maximum) allowable key size, and if applicable, using
an acceptable trust anchor and/or minSec value.
The configured authorization methods MUST include the trust anchor
authorization method, and MAY be additionally configured to
require CGA authorization.
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8.2 Router Advertisement Messages
All Router Advertisement messages are protected with SEND.
8.2.1 Sending Secure Router Advertisements
Secure Router Advertisement messages are sent as described in RFC
2461, with the additional requirements as listed in the following:
All Router Advertisement messages sent MUST contain a Timestamp
and Signature options. The Signature option MUST be configured to
protect the advertisement with the trust anchor authorization
method and MAY be configured to additionally protect it with the
CGA authorization method.
Router Advertisements sent in response to a Router Solicitation
MUST contain a copy of the Nonce option included in the
solicitation.
8.2.2 Receiving Secure Router Advertisements
Received Router Advertisement messages are processed as described in
RFC 2461, with the additional SEND-related requirements as listed in
the following:
Router Advertisement messages received without the Timestamp and
Signature options MUST be silently discarded.
Received Router Advertisements sent to a unicast destination
address without a Nonce option MUST be silently discarded.
The Signature option MUST be constructed with the configured
authorization method(s), the used key being within the configured
minimum (and maximum) allowable key size, and if applicable, using
an acceptable trust anchor and/or minSec value.
The configured authorization methods MUST include the trust anchor
authorization method, and MAY be additionally configured to
require CGA authorization.
8.3 Redirect Messages
All Redirect messages are protected with SEND.
8.3.1 Sending Redirects
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Secure Redirect messages are sent as described in RFC 2461, with the
additional requirements as listed in the following:
All Redirect messages sent MUST contain the Timestamp and
Signature options. The Signature option MUST be configured to use
the trust anchor authorization method, and MAY be additionally
configured to use the CGA method.
8.3.2 Receiving Redirects
Received Redirect messages are processed as described in RFC 2461,
with the additional SEND-related requirements as listed in the
following:
Redirect messages received without the Timestamp or Signature
options MUST be silently discarded.
The Signature option MUST be constructed with the configured
authorization method(s), the used key being within the configured
minimum (and maximum) allowable key size, and if applicable, using
an acceptable trust anchor and/or minSec value.
The configured authorization methods MUST include the trust anchor
authorization method, and MAY be additionally configured to
require CGA authorization.
The receiver MUST verify that the Redirect message comes from an
IP address to which the host may have earlier sent the packet that
the Redirect message now partially returns. That is, the source
address of the Redirect message must be the default router or the
on-link destination host for traffic sent to the destination of
the returned packet. If this is not the case, the message MUST be
silently discarded.
This step prevents a bogus router from sending a Redirect message
when the host is not using the bogus router as a default router.
8.4 Other Requirements
Hosts SHOULD use Authorization Delegation Discovery to learn the
certificate chain of their default router (or peer host), as
explained in Section 6. The receipt of a protected Router
Advertisement message for which no router Authorization Certificate
and certificate chain is available triggers Authorization Delegation
Discovery.
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9. Co-Existence of SEND and non-SEND nodes
During the transition to secure links or as a policy consideration,
network operators may want to run a particular link with a mixture of
secure and insecure nodes. Nodes that support SEND SHOULD support
the use of SEND and the legacy Neighbor Discovery Protocol at the
same time.
In a mixed environment, SEND nodes receive both secure and insecure
messages but give priority to "secured" ones. Here, the "secured"
messages are ones that contain a valid signature option, as specified
above, and "insecure" messages are ones that contain no signature
option.
SEND nodes send only secured messages. Legacy Neighbor Discovery
nodes will obviously send only insecure messages. Such nodes will (as
per RFC 2461 [6]) ignore the unknown options and will treat secured
messages in the same way as they treat insecure ones. Secured and
insecure nodes share the same network resources, such as prefixes and
address spaces.
In a mixed environment SEND routers and hosts follow the protocols
defined in RFC 2461 and RFC 2462 with the following exceptions:
All solicitations sent by SEND nodes MUST be secured.
Unsolicited Neighbor and Router Advertisements sent by a SEND
router MUST be secured.
Secured solicitations MUST contain the Nonce option. Secured
advertisements sent in response to a secured solicitation MUST
contain a copy of the Nonce option from the solicitation.
Unsolicited advertisements and ones sent in response to an
insecure solicitation MUST NOT contain the Nonce option.
A SEND node that uses the CGA authorization method for protecting
Neighbor Solicitations SHOULD perform Duplicate Address Detection
as follows. If Duplicate Address Detection indicates the
tentative address is already in use, generate a new tentative CGA
address. If after 3 consecutive attempts no non-unique address
was generated, log a system error and give up attempting to
generate an address for that interface.
When performing Duplicate Address Detection for the first
tentative address, accept both secured and insecure Neighbor
Advertisements and Solicitations received as response to the
Neighbor Solicitations. When performing Duplicate Address
Detection for the second or third tentative address, ignore
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insecure Neighbor Advertisements and Solicitations.
The node SHOULD have a configuration option that causes it to
ignore insecure advertisements even when performing Duplicate
Address Detection for the first tentative address. This
configuration option SHOULD be disabled by default. (This is
recovery mechanism for the unlikely case that attacks against the
first address become common.)
The Neighbor Cache, Prefix List and Default Router list entries
MUST have a secured/insecure flag that indicates whether the
message that caused the creation or last update of the entry was
secured or insecure. Received insecure messages MUST NOT cause
changes to existing secured entries in the Neighbor Cache, Prefix
List or Default Router List. Received secured messages cause an
update of the matching entries and flagging of them as secured.
The conceptual sending algorithm is modified so that an insecure
router is selected only if there is no reachable SEND router for
the prefix. That is, the algorithm for selecting a default router
favors reachable SEND routers over reachable non-SEND ones.
A SEND node SHOULD have a configuration option that causes it to
ignore all insecure ND, RD and Redirect messages. (This can be
used to enforce SEND-only networks.)
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10. Performance Considerations
The computations related to the Signature option are computationally
relatively expensive. In the application which Signature option has
been designed for, however, the nodes typically have the need to
perform only a few signature operations as they enter a link, and a
few operations as they find a new on-link peer with which to
communicate.
Routers are required to perform a larger number of operations,
particularly when the frequency of router advertisements is high due
to mobility requirements. Still, the number of required signature
operations is on the order of a few dozen ones per second, some of
which can be precomputed as discussed below. A large number of
router solicitations may cause higher demand for performing
asymmetric operations, although RFC 2461 limits the rate at which
responses to solicitations can be sent.
Signatures related to the use of the Signature option be precomputed
for Multicast Neighbor and Router Advertisements. Typically,
solicited advertisements are sent to the unicast address from which
the solicitation was sent. Given that the IPv6 header is covered by
the signature, it is typically not possible to precompute
solicited-for advertisements.
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11. Security Considerations
11.1 Threats to the Local Link Not Covered by SEND
SEND does not compensate for an insecure link layer. In particular,
there is no cryptographic binding in SEND between the link layer
frame address and the IPv6 address. On an insecure link layer that
allows nodes to spoof the link layer address of other nodes, an
attacker could disrupt IP service by sending out a Neighbor
Advertisement having the source address on the link layer frame of a
victim, a valid CGA address and a valid signature corresponding to
itself, and a Target Link-layer Address extension corresponding to
the victim. The attacker could then proceed to cause a traffic
stream to bombard the victim in a DoS attack. To protect against
such attacks, link layer security MUST be used. An example of such
for 802 type networks is port-based access control defined in the
802.1X standard [34].
Specifically, the 802.1X standard provides a mechanism by which a
nodes can be authenticated to a particular point of attachment to a
LAN (called a "port" in the standard). If the MAC on frames sent by a
node does not correspond to the MAC of the node originally
authenticated to this port, then the point of attachment drops the
frames. Authorization to use the port is determined by the MAC
address of the node that originally authenticated to the port. The
way 802.1X protects against this attack is that, if a node
authenticated to a particular port attempts to spoof the MAC address
of another node, the port will drop the frames. Naturally, this
requires that all ports by which nodes can attach to the LAN use
802.1X authentication, and that all node physically attach through a
port, as is the case with 802.3 switched LAN. For shared media, such
as multiple nodes authenticated through the same 802.11 AP (which
acts as a single port for all nodes), other measures are necessary,
since an attacker on the wireless link can spoof the MAC address of a
victim on the same wireless link.
802.1X does not provide protection for the layer 2 frame - layer 3
packet address binding in traffic (that is, real time filtering to
check this binding), and neither does SEND. 802.1X provides
authentication and filtering of MAC address to port; SEND provides
protection for the layer 2 - layer 3 binding information in the
Neighbor Discovery packet, via the CGA address (authorization to use
the address via the public key) and the signature on the packet
(authentication of contents as from authorized IP address possessor).
Prior to participating in Neighbor Discovery and Duplicate Address
Detection, nodes must subscribe to the link-scoped All-Nodes
Multicast Group and the Solicited-Node Multicast Group for the
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address that they are claiming for their addresses; RFC 2461 [6].
Subscribing to a multicast group requires that the nodes use MLD
[20]. MLD contains no provision for security. An attacker could
send an MLD Done message to unsubscribe a victim from the
Solicited-Node Multicast address. However, the victim should be able
to detect such an attack because the router sends a
Multicast-Address-Specific Query to determine whether any listeners
are still on the address, at which point the victim can respond to
avoid being dropped from the group. This technique will work if the
router on the link has not been compromised. Other attacks using MLD
are possible, but they primarily lead to extraneous (but not
overwhelming) traffic.
11.2 How SEND Counters Threats to Neighbor Discovery
The SEND protocol is designed to counter the threats to IPv6 Neighbor
Discovery, as outlined in [27]. The following subsections contain a
regression of the SEND protocol against the threats, to illustrate
what aspects of the protocol counter each threat.
11.2.1 Neighbor Solicitation/Advertisement Spoofing
This threat is defined in Section 4.1.1 of [27]. The threat is that
a spoofed Neighbor Solicitation or Neighbor Advertisement causes a
false entry in a node's Neighbor Cache. There are two cases:
1. Entries made as a side effect of a Neighbor Solicitation or
Router Solicitation. There are two cases:
1. A router receiving a Router Solicitation with a firm IPv6
source address and a Target Link-Layer Address extension
inserts an entry for the IPv6 address into its Neighbor
Cache.
2. A node doing Duplicate Address Detection (DAD) that receives
a Neighbor Solicitation for the same address regards the
situation as a collision and ceases to solicit for the
address.
2. Entries made as a result of a Neighbor Advertisement sent as a
response to a Neighbor Solicitation for purposes of on-link
address resolution.
11.2.1.1 Solicitations with Effect
SEND counters the threat of solicitations with effect in the
following ways:
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1. As discussed in Section 5, SEND nodes preferably send Router
Solicitations with a CGA address and a Signature option, which
the router can verify, so the Neighbor Cache binding is correct.
If a SEND node must send a Router Solicitation with the
unspecified address, the router will not update its Neighbor
Cache, as per RFC 2461.
See Section 11.2.5, below, for discussion about replay protection and
timestamps.
11.2.1.2 Address Resolution
SEND counters attacks on address resolution by requiring that the
responding node include a signature option on the packet, and that
the node's interface identifier either be a CGA, or that the node be
able to produce a certificate authorizing that node to use the public
key.
The Neighbor Solicitation and Advertisement pairs implement a
challenge-response protocol, as explained in Section 7 and discussed
in Section 11.2.5 below.
11.2.2 Neighbor Unreachability Detection Failure
This attack is described in Section 4.1.2 of [27]. SEND counters
this attack by requiring a node responding to Neighbor Solicitations
sent as NUD probes to include a Signature option and proof of
authorization to use the interface identifier in the address being
probed. If these prerequisites are not met, the node performing NUD
discards the responses.
11.2.3 Duplicate Address Detection DoS Attack
This attack is described in Section 4.1.3 of [27]. SEND counters
this attack by requiring the Neighbor Advertisements sent as
responses to DAD to include a Signature option and proof of
authorization to use the interface identifier in the address being
tested. If these prerequisites are not met, the node performing DAD
discards the responses.
When a SEND node is used on a link that also connects to non-SEND
nodes, the SEND node ignores any insecure Neighbor Solicitations or
Advertisements that may be send by the non-SEND nodes. This protects
the SEND node from DAD DoS attacks by non-SEND nodes or attackers
simulating to non-SEND nodes, at the cost of a potential address
collision between a SEND node and non-SEND node. The probability and
effects of such an address collision are discussed in [26].
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11.2.4 Router Solicitation and Advertisement Attacks
These attacks are described in Sections 4.2.1, 4.2.4, 4.2.5, 4.2.6,
and 4.2.7 of [27]. SEND counters these attacks by requiring Router
Advertisements to contain a Signature option, and that the signature
is calculated using the public key of a node that can prove its
authorization to route the subnet prefixes contained in any Prefix
Information Options. The router proves its authorization by showing
a certificate containing the specific prefix or the indication that
the router is allowed to route any prefix. A Router Advertisement
without these protections is dropped.
SEND does not protect against brute force attacks on the router, such
as DoS attacks, or compromise of the router, as described in Sections
4.4.2 and 4.4.3 of [27].
11.2.5 Replay Attacks
This attack is described in Section 4.3.1 of [27]. SEND protects
against attacks in Router Solicitation/Router Advertisement and
Neighbor Solicitation/Neighbor Advertisement transactions by
including a Nonce option in the solicitation and requiring the
advertisement to include a matching option. Together with the
signatures this forms a challenge-response protocol. SEND protects
against attacks from unsolicited messages such as Neighbor
Advertisements, Router Advertisements, and Redirects by including a
Timestamp option. A window of vulnerability for replay attacks
exists until the timestamp expires.
When timestamps are used, SEND nodes are protected against replay
attacks as long as they cache the state created by the message
containing the timestamp. The cached state allows the node to
protect itself against replayed messages. However, once the node
flushes the state for whatever reason, an attacker can re-create the
state by replaying an old message while the timestamp is still valid.
Since most SEND nodes are likely to use fairly coarse grained
timestamps, as explained in Section 5.4.1, this may affect some
nodes.
11.2.6 Neighbor Discovery DoS Attack
This attack is described in Section 4.3.2 of [27]. In this attack,
the attacker bombards the router with packets for fictitious
addresses on the link, causing the router to busy itself with
performing Neighbor Solicitations for addresses that do not exist.
SEND does not address this threat because it can be addressed by
techniques such as rate limiting Neighbor Solicitations, restricting
the amount of state reserved for unresolved solicitations, and clever
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cache management. These are all techniques involved in implementing
Neighbor Discovery on the router.
11.3 Attacks against SEND Itself
The CGAs have a 59-bit hash value. The security of the CGA mechanism
has been discussed in [26].
Some Denial-of-Service attacks against NDP and SEND itself remain.
For instance, an attacker may try to produce a very high number of
packets that a victim host or router has to verify using asymmetric
methods. While safeguards are required to prevent an excessive use
of resources, this can still render SEND non-operational.
When CGA protection is used, SEND deals with the DoS attacks using
the verification process described in Section 5.3.2. In this process,
a simple hash verification of the CGA property of the address is
performed first before performing the more expensive signature
verification.
When trust anchors and certificates are used for address validation
in SEND, the defenses are not quite as effective. Implementations
SHOULD track the resources devoted to the processing of packets
received with the Signature option, and start selectively dropping
packets if too many resources are spent. Implementations MAY also
first drop packets that are not protected with CGA.
The Authorization Delegation Discovery process may also be vulnerable
to Denial-of-Service attacks. An attack may target a router by
requesting a large number of delegation chains to be discovered for
different trust anchors. Routers SHOULD defend against such attacks
by caching discovered information (including negative responses) and
by limiting the number of different discovery processes they engage
in.
Attackers may also target hosts by sending a large number of
unnecessary certificate chains, forcing hosts to spend useless memory
and verification resources for them. Hosts can defend against such
attacks by limiting the amount of resources devoted to the
certificate chains and their verification. Hosts SHOULD also
prioritize advertisements that sent as a response to their
solicitations above unsolicited advertisements.
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12. IANA Considerations
This document defines two new ICMP message types, used in
Authorization Delegation Discovery. These messages must be assigned
ICMPv6 type numbers from the informational message range:
o The Delegation Chain Solicitation message, described in Section
6.1.
o The Delegation Chain Advertisement message, described in Section
6.2.
This document defines six new Neighbor Discovery Protocol [6]
options, which must be assigned Option Type values within the option
numbering space for Neighbor Discovery Protocol messages:
o The Trust Anchor option, described in Section 6.3.
o The Certificate option, described in Section 6.4.
o The CGA option, described in Section 5.2.
o The Signature option, described in Section 5.3.
o The Timestamp option, described in Section 5.4.1.
o The Nonce option, described in Section 5.4.2.
This document defines a new 128-bit CGA Message Type [26] value,
0xXXXX XXXX XXXX XXXX XXXX XXXX XXXX XXXX (To be generated randomly).
XXX: Use existing name spaces for these?
This document defines a new name space for the Name Type field in the
Trust Anchor option. Future values of this field can be allocated
using standards action [5].
Another new name space is allocated for the Cert Type field in the
Certificate option. Future values of this field can be allocated
using standards action [5].
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Normative References
[1] Mockapetris, P., "Domain names - concepts and facilities", STD
13, RFC 1034, November 1987.
[2] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[3] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
November 1998.
[4] Piper, D., "The Internet IP Security Domain of Interpretation
for ISAKMP", RFC 2407, November 1998.
[5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October
1998.
[6] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.
[7] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[8] Conta, A. and S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6)
Specification", RFC 2463, December 1998.
[9] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001.
[10] Bassham, L., Polk, W. and R. Housley, "Algorithms and
Identifiers for the Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile", RFC
3279, April 2002.
[11] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet X.509
Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile", RFC 3280, April 2002.
[12] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)
Addressing Architecture", RFC 3513, April 2003.
[13] Lynn, C., "X.509 Extensions for IP Addresses and AS
Identifiers", draft-ietf-pkix-x509-ipaddr-as-extn-02 (work in
progress), September 2003.
[14] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support in
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IPv6", draft-ietf-mobileip-ipv6-24 (work in progress), July
2003.
[15] RSA Laboratories, "RSA Encryption Standard, Version 2.1", PKCS
1, November 2002.
[16] National Institute of Standards and Technology, "Secure Hash
Standard", FIPS PUB 180-1, April 1995, <http://
www.itl.nist.gov/fipspubs/fip180-1.htm>.
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Informative References
[17] Postel, J., "Internet Control Message Protocol", STD 5, RFC
792, September 1981.
[18] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37, RFC
826, November 1982.
[19] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
RFC 2409, November 1998.
[20] Deering, S., Fenner, W. and B. Haberman, "Multicast Listener
Discovery (MLD) for IPv6", RFC 2710, October 1999.
[21] Farrell, S. and R. Housley, "An Internet Attribute Certificate
Profile for Authorization", RFC 3281, April 2002.
[22] Arkko, J., "Effects of ICMPv6 on IKE",
draft-arkko-icmpv6-ike-effects-02 (work in progress), March
2003.
[23] Arkko, J., "Manual Configuration of Security Associations for
IPv6 Neighbor Discovery", draft-arkko-manual-icmpv6-sas-02
(work in progress), March 2003.
[24] Droms, R., "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress),
November 2002.
[25] Kent, S., "IP Encapsulating Security Payload (ESP)",
draft-ietf-ipsec-esp-v3-06 (work in progress), July 2003.
[26] Aura, T., "Cryptographically Generated Addresses (CGA)",
draft-ietf-send-cga-01 (work in progress), August 2003.
[27] Nikander, P., "IPv6 Neighbor Discovery trust models and
threats", draft-ietf-send-psreq-03 (work in progress), April
2003.
[28] Montenegro, G. and C. Castelluccia, "SUCV Identifiers and
Addresses", draft-montenegro-sucv-03 (work in progress), July
2002.
[29] International Organization for Standardization, "The Directory
- Authentication Framework", ISO Standard X.509, 2000.
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[30] O'Shea, G. and M. Roe, "Child-proof Authentication for MIPv6",
Computer Communications Review, April 2001.
[31] Nikander, P., "Denial-of-Service, Address Ownership, and Early
Authentication in the IPv6 World", Proceedings of the Cambridge
Security Protocols Workshop, April 2001.
[32] Arkko, J., Aura, T., Kempf, J., Mantyla, V., Nikander, P. and
M. Roe, "Securing IPv6 Neighbor Discovery", Wireless Security
Workshop, September 2002.
[33] Montenegro, G. and C. Castelluccia, "Statistically Unique and
Cryptographically Verifiable (SUCV) Identifiers and Addresses",
NDSS, February 2002.
[34] Institute of Electrical and Electronics Engineers, "Local and
Metropolitan Area Networks: Port-Based Network Access Control",
IEEE Standard 802.1X, September 2001.
Authors' Addresses
Jari Arkko
Ericsson
Jorvas 02420
Finland
EMail: jari.arkko@ericsson.com
James Kempf
DoCoMo Communications Labs USA
181 Metro Drive
San Jose, CA 94043
USA
EMail: kempf@docomolabs-usa.com
Bill Sommerfeld
Sun Microsystems
1 Network Drive UBUR02-212
Burlington, MA 01803
USA
EMail: sommerfeld@east.sun.com
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Brian Zill
Microsoft
USA
EMail: bzill@microsoft.com
Pekka Nikander
Ericsson
Jorvas 02420
Finland
EMail: Pekka.Nikander@nomadiclab.com
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Appendix A. Contributors
Tuomas Aura contributed the transition mechanism specification in
Section 9.
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Appendix B. IPR Considerations
The optional CGA part of SEND uses public keys and hashes to prove
address ownership. Several IPR claims have been made about such
methods.
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Appendix C. Cache Management
In this section we outline a cache management algorithm that allows a
node to remain partially functional even under a cache filling DoS
attack. This appendix is informational, and real implementations
SHOULD use different algorithms in order to avoid he dangers of
monocultural code.
There are at least two distinct cache related attack scenarios:
1. There are a number of nodes on a link, and someone launches a
cache filling attack. The goal here is clearly make sure that
the nodes can continue to communicate even if the attack is going
on.
2. There is already a cache filling attack going on, and a new node
arrives to the link. The goal here is to make it possible for
the new node to become attached to the network, inspite of the
attack.
From this point of view, it is clearly better to be very selective in
how to throw out entries. Reducing the timestamp Delta value is very
discriminative against those nodess that have a large clock
difference, while an attacker can reduce its clock difference into
arbitrarily small. Throwing out old entries just because their clock
difference is large seems like a bad approach.
A reasonable idea seems to be to have a separate cache space for new
entries and old entries, and under an attack more eagerly drop new
cache entries than old ones. One could track traffic, and only allow
those new entries that receive genuine traffic to be converted into
old cache entries. While such a scheme will make attacks harder, it
will not fully prevent them. For example, an attacker could send a
little traffic (i.e. a ping or TCP syn) after each NS to trick the
victim into promoting its cache entry to the old cache. Hence, the
node may be more intelligent in keeping its cache entries, and not
just have a black/white old/new boundary.
It also looks like a good idea to consider the sec parameter when
forcing cache entries out, and let those entries with a larger sec a
higher chance of staying in.
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Appendix D. Comparison to AH-Based Approach
This approach has the following benefits compared to the previous
Working Group document approach:
o The full implementation of the security mechanism, including
Nonces and CGAs, exists within one module. There is no need to
analyze the security of the mechanism across NDP, IPsec, and CGA
layers.
o The CGA part of the solution has been separated into its own
specification. This is possible because the CGA handling is done
in its own option. (The authorization method configuration flag
is the only thing common to the CGA and Signature options.)
o No extensions or modifications of IPsec processing are required:
SPD entries are not required to distinguish ICMP types, AH does
not need to support public keys or CGAs, and destination address
acgnostic security associations are not needed.
o It is not necessary to allocate a new multicast address to
represent the Solicited-Node multicast address for SEND nodes.
o It is not necessary to change the Neighbor Discovery behavior with
regards to the use of the unspecified address. Since all
information is available within the Neighbor Discovery messages,
unspecified source addresses can be used, still being able to
correlate the CGA property with the Target Address in a Neighbor
Solicitation during Duplicate Address Detection.
o The transition mechanisms for links with both SEND and non-SEND
nodes are significantly simpler. In particular, non-SEND nodes
will be able to receive DAD probes and other messages sent by the
SEND nodes.
o Only a single set of Neighbor Discovery messages from the router
needs to be transmitted on a link. This helps avoid extra
overhead for mobility beacons and other frequently occurring
messaging.
o Given that the asymmetric computations required in SEND are
computationally expensive, it is necessary to control the number
of these operations in order to avoid Denial-of-Service attacks.
This control is easier to arrange with "application layer"
information. For instance, a router need not verify more Router
Solicitations with an unspecified source address than it can
respond to according to the RFC 2461 rules.
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o There is no need for an API to communicate certificate chains
requests and certificate chains between the IPsec and Neighbor
Discovery modules.
Also, a good implementation of SEND would not require the user to
configure it (beyond perhaps enabling it). In order to achieve
this with IPsec, a set of policy entries needs to be automatically
created upon system start.
o There is no need for the CGA parameters to be stored both in the
IPsec and Neighbor Discovery modules, where they are needed for
the construction of Authentication Headers and addresses,
respectively.
o It is not necessary to change existing BITS or BITW IPsec
implementations to support SEND and AH_RSA_Sig. There would have
been two problems associated with such changes:
* A SEND implementation in such environment could not proceed
until this modification were completed.
* Typical hardware that processes IPsec packets may not be easily
changed to process asymmetric transforms. (Of course, such
packets can be passed to the main CPU at the node, assuming
this can easily be done in the given implementation.)
o In addition, many IPsec implementations are highly optimized
because they are on the fast path for packet processing. For
example, the Linux implementation runs in the kernel interrupt
thread. Some of the SEND modifications might have required IPsec
processing to wait on a semaphore while, for example, a
certificate chain is fetched, an operation that takes place out of
band in regular IPsec processing because it is done using IKE.
While it might have been possible that the implemenation could
have been arranged so that general IPsec processing wasqn't
impacted, the resulting code would have been more complex.
The use of IPsec to protect NDP would have been possible, but the
limits and capabilities of IPsec would have to be stretched. Small
changes in the NDP protocol (or our understanding of the issues)
might have caused a situation which had no longer been easily handled
when the "application" and the security existed at different layers.
Although IPsec as defined in RFC 2402 just defines a header format,
RFC 2401 and the ensuing years of implementation have evolved a
complex interconnected set of components for IPsec which would have
required some modification to accommodate SEND.
On the other hand, IPsec is the current solution for securing NDP in
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the original NDP RFCs. Even if the current IPsec can be used only in
very limited networks to secure NDP, it could have been argued that
it would have been logical to continue its use. Also, the existence
of an asymmetric transform in IPsec would have been potentially
useful in other contexts as well.
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