Transaction SIGnature (TSIG) using CGA Algorithm in IPv6
draft-rafiee-intarea-cga-tsig-06
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Expired".
|
|
|---|---|---|---|
| Authors | Hosnieh Rafiee , Martin von Loewis , Christoph Meinel | ||
| Last updated | 2013-09-27 | ||
| Replaces | draft-rafiee-cga-tsig | ||
| RFC stream | (None) | ||
| Formats | |||
| Reviews | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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| Send notices to | (None) |
draft-rafiee-intarea-cga-tsig-06
DNS Extensions H. Rafiee
INTERNET-DRAFT M. v. Loewis
Updates RFC 2845 (if approved) C. Meinel
Intended Status: Standards Track Hasso Plattner Institute
Expires: March 27, 2014 September 27, 2013
Transaction SIGnature (TSIG) using CGA Algorithm in IPv6
<draft-rafiee-intarea-cga-tsig-06.txt>
Abstract
This document describes a new mechanism that can be used to reduce
the need for human intervention during DNS authentication and secure
DNS authentication in various scenarios such as the DNS
authentication of resolvers to stub resolvers, authentication during
zone transfers, authentication of root DNS servers to recursive DNS
servers, and authentication during the FQDN (RFC 4703) update.
Especially in the last scenario, i.e., FQDN, if the node uses the
Neighbor Discovery Protocol (NDP) (RFC 4861, RFC 4862), unlike the
Dynamic Host Configuration Protocol (DHCP) (RFC 3315), the node has
no way of updating his FQDN records on the DNS and has no means for a
secure authentication with the DNS server. While this is a major
problem in NDP-enabled networks, this is a minor problem in DHCPv6.
This is because the DHCP server updates the FQDN records on behalf of
the nodes on the network.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute working
documents as Internet-Drafts. The list of current Internet-Drafts is
at http://datatracker.ietf.org/drafts/current.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 27, 2014.
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Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. This document is subject to
BCP 78 and the IETF Trust's Legal Provisions Relating to IETF
Documents (http://trustee.ietf.org/license-info) in effect on the
date of publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5
5. CGA-TSIG Applications . . . . . . . . . . . . . . . . . . . . 5
5.1. IP Spoofing . . . . . . . . . . . . . . . . . . . . . . 6
5.2. DNS Dynamic Update Spoofing . . . . . . . . . . . . . . . 6
5.3. Resolver Configuration Attack . . . . . . . . . . . . . . 7
5.4. Exposing Shared Secret . . . . . . . . . . . . . . . . . 7
5.5. Replay attack . . . . . . . . . . . . . . . . . . . . . . 7
6. Algorithm Overview . . . . . . . . . . . . . . . . . . . . . 7
6.1. The CGA-TSIG DATA structure . . . . . . . . . . . . . . 7
6.2. Generation of CGA-TSIG DATA . . . . . . . . . . . . . . . 9
7. Authentication During Zone Transfer . . . . . . . . . . . . . 11
7.1. Verification process . . . . . . . . . . . . . . . . . . 12
8. Authentication During the FQDN or PTR Update . . . . . . . . 13
8.1. Verification Process . . . . . . . . . . . . . . . . . . 14
9. Authentication During Query Resolving (stub to recursive) . . 14
9.1. Verification process . . . . . . . . . . . . . . . . . . 15
10. Authentication During Query Resolving (Auth. to recursive) . 16
11. No cache parameters available or SeND is not supported . . . 16
12. Security Considerations . . . . . . . . . . . . . . . . . . . 16
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
14. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . 18
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
16.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 19
16.2. Informative . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
Transaction SIGnature (TSIG) [RFC2845] is a protocol that provides
endpoint authentication and data integrity through the use of one-way
hashing and shared secret keys in order to establish a trust
relationship between two/group of hosts, which can be either a client
and a server, or two servers. The TSIG keys, which are manually
exchanged between a group of hosts, need to be maintained in a secure
manner. This protocol is today mostly used to secure a Dynamic
Update, or to give assurance to the slave name server that the zone
transfer is from the original master name server and that it has not
been spoofed by hackers. It does this by verifying the signature
using a cryptographic key that is shared with the receiver.
It is possible to extend the TSIG protocol through the use of newly
defined algorithms. This document proposes the use of
Cryptographically Generated Addresses (CGA) [RFC3972] as a new
algorithm in the TSIG Resource Record (RR). CGA is an important
option available in Secure Neighbor Discovery (SeND) [RFC3971], which
provides nodes with the necessary proof of IP address ownership by
providing a cryptographic binding between a host and its IP address
without the need for the introduction of a new infrastructure. CGA is
a one-way hashing algorithm used to generate Interface IDs for IPv6
addresses in a secure manner. An interface ID consists of the
rightmost 64 bits of the 128 bit IPv6 address. CGA verifies the
ownership of the sender's IP address by finding a relationship
between the sender's IP address and his public key [1,2].
+------------------------------------------------+
| Subnet Prefix | Interface ID |
| (8 octets) | (8 octets) |
+------------------------------------------------+
Figure 1 IPv6 addresses
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC 2119 significance.
3. Terminology
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The terms used in this document have the following standard meaning:
- Name server: A server that supports DNS service.
- Resolver/recursive DNS server: A resolver/recursive name server
responds to queries where the query does not contain an entry for the
node in its database. It first checks its own records and cache for
the answer to the query and then, if it cannot find an answer there,
it may recursively query name servers higher up in the hierarchy and
then pass the response back to the originator of the query. This is
known as a recursive query or recursive lookup.
- Stub resolver: A specific kind of DNS resolver that is unable to
resolve the queries recursively. So, it relies on a recursive DNS
resolver to resolve the queries.
- Authoritative: An authoritative name server provides the answers to
DNS queries. For example, it would respond to a query about a mail
server IP address or website IP address. It provides original,
first-hand, definitive answers (authoritative answers) to DNS
queries. It does not provide 'just cached' answers that were obtained
from another name server. Therefore it only returns answers to
queries about domain names that are installed in its system
configuration.
There are two types of Authoritative Name Servers:
1. Master server (primary name server): A master server stores the
original master copies of all zone records. A host master is only
allowed to change the master server?s zone records. Each slave server
gets updated via a special automatic updating mechanism within the
DNS protocol. All slave servers maintain identical copies of the
master records.
2. Slave server (secondary name server): A slave server is an exact
replica of the master server. It is used to share the DNS server's
load and to improve DNS zone availability in cases where the master
server fails. It is recommended that there be at least 2 slave
servers and one master server for each domain name.
- Root DNS server: An authoritative DNS server for a specific root
domain. For example, .com
- Client: a client can be any computer (server, laptop, etc) that
only supports stub DNS servers and not other DNS services. It can be
a mail server, web server or a laptop computer.
- Node: a node can be anything such as a client, a DNS server
(resolver, authoritative) or a router.
- Host: all nodes except routers
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4. Problem Statement
The authentication during any DNS query process is solely based on
the source IP address when no secure mechanism is in use either
during the DNS update (zone transfer, FQDN update) or during the DNS
query resolving process. This makes the DNS query process vulnerable
to several types of spoofing attacks -- man in the middle, reflector
, source IP spoofing, etc. One example is the problem that exists
between a client and a DNS resolver. When a client sends a DNS query
to a resolver, an attacker can send a response to this client
containing the spoofed source IP address for this resolver. The
client checks the resolver's source IP address for authentication. If
the attacker spoofed the resolver's IP address, and if the attacker
responds faster than the legitimate resolver, then the client's cache
will be updated with the attacker's response. The client does not
have any way to authenticate the resolver.
If DNSSEC (RFC 6840) or TSIG, as a security mechanism is in use, then
the problem would be the manual step required for the configuration.
For instance when a DNSSEC needs to sign the zone offline. TSIG
secures this process by providing the transaction level
authentication necessary by the use of a shared secret. But, the
current problem with using TSIG is that manual processing is required
in order to generate and exchange the shared secrets. This is
because, in TSIG, the shared secret exchange is done offline.
Currently there is little deployment of TSIG for resolver
authentication with clients. One reason is that resolvers respond to
anonymous queries and can be located in any part of the network. A
second reason is that the manual TSIG process makes it difficult to
configure each new client with the shared secret of the resolver.
Another catastrophic problem with TSIG would be when this shared
secret, that is shared between a group of hosts, leaks and makes it
necessary to repeat this manual step. The reason is, that for each
group of hosts there needs to be one shared secret and the
administrator will need to manually add it to the DNS configuration
file for each of these hosts. This manual process will need to be
invoked in the case where one of these hosts is compromised and the
shared secret is well known to the attacker. It will also have to be
invoked in the case where any of these hosts needs to change their IP
addresses, because of different reasons such as privacy issues, as
explained in RFC 4941 [RFC4941], or when moving to another subnet
within the same network, etc. Therefore, the problem that exists
today with the authentication processes used in different scenarios
is what this document addresses. The various scenarios include
authentication during zone transfer, authentication of the nodes
during DNS query resolving and authentication during updating PTR and
FQDN (RFC 4703).
5. CGA-TSIG Applications
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The purpose of CGA-TSIG [7] is to minimize the amount of human
intervention required to accomplish shared secret or key exchange
and, as a byproduct, to reduce the process's vulnerability to attacks
introduced by human errors (during changing the DNS configuration)
when Secure Neighbor Discovery (SeND) is used for addressing purposes
or when SeND is not available for use.
As explained in a prior section, CGA-TSIG can be used in different
scenarioes. For the FQDN update scenario CGA-TSIG is useful in
dynamic networks where the nodes want to change their IP addresses
frequently in order to maintain privacy. If the Dynamic Host
Configuration Protocol (DHCP) is in use, then the DHCP server can do
this update on behalf of the nodes in this network on a DNS server
but in Neighbor Discovery Protocol (NDP), there is no feature
available that allows the host security update process for its own
FQDN. CGA-TSIG can be a solution.
For the resolver scenario, usually the the resolver can add the TSIG
Resource Record (RR) to the DNS query response and use the CGA-TSIG
algorithm in order to permit a useful authentication of the result.
CGA-TSIG assures the client that the query response comes from the
true originator and not from an attacker. It also ensures the
integrity of the data by signing the data.
There are several types of attack that CGA-TSIG can prevent. Here we
will evaluate some of them. The use of CGA-TSIG will also reduce the
number of messages needed in exchange between a client and a server
in order to establish a secure channel. To exchange the shared secret
between a DNS resolver and a client, when TSIG is used, a minimum of
four messages are required for the establishment of a secure channel.
Modifying RFC 2845 to use CGA-TSIG will decrease the number of
messages needed in this exchange. The messages used in RFC 2930 (TKEY
RR) are not needed when CGA-TSIG is used.
5.1. IP Spoofing
During the DNS Update process or the query resolving process it is
important that both communicating parties know that the one that they
are communicating with is the actual owner of that IP address and
that the messages are not being sent from a spoofed IP address. This
can be accomplished by the use of the CGA algorithm which utilizes
the node for IP address verification of other nodes.
5.2. DNS Dynamic Update Spoofing
Dynamic Update Spoofing is eliminated because the signature contains
both the CGA parameters and the DNS update message. This will offer
proof of the sender's IP address ownership (CGA parameters) and the
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validity of the update message.
5.3. Resolver Configuration Attack
When using CGA-TSIG, the DNS server, or the client, would not need
further configuration. This would reduce the possibility of human
errors being introduced into the DNS configuration file. Since this
type of attack is predicated on human error, the chances of it
occurring, when this extension is used, are minimized.
5.4. Exposing Shared Secret
Using CGA-TSIG will decrease the number of manual steps required in
generating the new shared secret and in exchanging it among the hosts
where the old shared secret was shared between them for updating
purposes. This manual step is required after a leakage has occurred
of the shared secret to an attacker via any of these hosts.
5.5. Replay attack
Using the Time Signed value in the signature modifies the content of
the signature each time the node generates and sends it to the DNS
server. If the attacker tries to spoof this value with another
timestamp, to show that the update message is current, the DNS server
checks this message by verifying the signature. In this case, the
verification process will fail thus also preventing the replay
attack.
6. Algorithm Overview
The following sections explain the use of CGA or any other future
algorithm in place of CGA for securing the DNS process by adding a
CGA-TSIG data structure as an option to the TSIG Resource Record
(RR).
6.1. The CGA-TSIG DATA structure
The CGA-TSIG data structure SHOULD be added to the Other DATA section
of the RDATA field in the TSIG Resource Record (RR) (see figures 2
and 3). The DNS RRTYPE must be set to TSIG [RFC2845]. The RDATA
Algorithm Name MUST be set to CGA-TSIG. A detailed explanation of the
standard RDATA fields can be found in section 2.3 RFC 2845. This
document focuses only on the new structure added to the Other DATA
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section. These new fields are CGA-TSIG Len and CGA-TSIG DATA. The
TSIG RR is added to an additional section of the DNS message. If
another algorithm is used in place of CGA for SeND, such as SSAS [4 ,
5], then the CGA-TSIG Len will be the length for the parameters of
this algorithm and CGA-TSIG DATA will consist of the parameters
required for verification of that algorithm, like signature, public
key, etc.
+---------------------------------------+
| Algorithm Name |
| (CGA-TSIG) |
+---------------------------------------+
| Time Signed |
| |
+---------------------------------------+
| Fudge |
| |
+---------------------------------------+
| MAC Size |
| |
+---------------------------------------+
| Mac |
| |
+---------------------------------------+
| Original ID |
| |
+---------------------------------------+
| Error |
| |
+---------------------------------------+
| OTHER LEN |
| |
+---------------------------------------+
| OTHER DATA |
| |
+---------------------------------------+
Figure 2 Modified TSIG RDATA
The CGA-TSIG DATA Field and the CGA-TSIG Len will occupy the first
two slots of Other DATA. Figure 3 shows the layout.
+---------------------------------------+
| CGA-TSIG Len |
| |
+---------------------------------------+
| CGA-TSIG DATA |
| |
+---------------------------------------+
| Other Options |
| |
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+---------------------------------------+
Figure 3 Other DATA section of RDATA field
CGA-TSIG DATA Field Name Data Type Notes
--------------------------------------------------------------
Algorithm type u_int16_t Name of the algorithm
[RFC3972] RSA (by default) CGA
type u_int16_t Name of the algorithm used in
SEND
IP tag 16 octet the tag used to identify the IP
address
Parameters Len Octet the length of CGA parameters
Parameters variable CGA parameters Section 3 RFC 3972
Signature Len Octet the length of CGA signature
Signature variable Section 3.2.1 This document
old pubkey Len variable the length of old public key
field
old pubkey variable Old public key
old Signature Len variable the length of old signature field
old Signature variable Old signature generated by old
public key.
Type indicates the Interface ID generation algorithm that was used in
SeND. This field allows for the use of future, optional algorithms in
SeND. The default value for CGA is 1. The IP tag is a node's old IP
address. A client's public key can be associated with several IP
addresses on a server. The DNS server, or the DNS message verifier
node, SHOULD store the IP addresses and the public keys so as to
indicate their association to each other. If a client wants to add
RRs to the server by using a new IP address, then the IP tag field
will be set to binary zeros. The server will then store the new IP
address that was passed to it in storage. If the client wants to
replace an existing IP address in a DNS server with a new one, then
the IP tag field will be populated with the IP address which is to be
replaced. The DNS server will then look for the IP address referenced
by the IP tag stored in its storage and replace that IP address with
the new one. This enables the client to update his own RRs using
multiple IP addresses while, at the same time, giving him the ability
to change IP addresses. If a node changes its public key in order to
maintain privacy, then it MUST add the old public key to the old
pubkey field. It MUST also retrieve the current time from Time Signed
field, sign it using the old private key, and then add the digest
(signature) to the old signature field. This enables the verifier
node to authenticate a host with a new public key. The detailed
verification steps are explained in sections 5.1, 6.1 and 7.1.
6.2. Generation of CGA-TSIG DATA
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In order to use CGA-TSIG as an authentication approach, some of the
parameters need to be cached during IP address generation. If no
parameters are available in cache, please see section 8. If the Type
(section 4.1) is CGA, then the parameters that SHOULD be cached are
the modifier, algorithm type, location of the public/private keys and
the IP addresses of this host generated by the use of CGA.
1.Obtain required parameters from cache.
The CGA-TSIG algorithm obtains the old IP address, modifier, subnet
prefix, and public key from cache. It concatenates the old IP address
with the CGA parameters, i.e., modifier, subnet prefix, public key
and collision count (the order of CGA parameters are shown in section
3 RFC 3972). If the old IP address is not available, then CGA-TSIG
must set the old IP address (IP tag) to zero.
Note: If the node is a DNS server (resolver or authoritative DNS
server) and it does not support SeND, but the goal is to use this
algorithm, then It is possible to use a script to generate the CGA
parameters , which are needed to manually configure this server's IP
address. Then this server can make use these parameters for
authentication purposes.
2. Generate signature
For signature generation, all CGA parameters (modifier, public key,
collision count and subnet prefix), that are concatenated with the
DNS update message, the IP tag and the Time Signed field, are signed
by using a RSA algorithm, the default, or any future algorithm used
in place of RSA, and the private key which was obtained from cache in
the first step. This signature must be added to the signature field
of the CGA-TSIG DATA. Time Signed is the same timestamp as is used in
RDATA. This value is the number of seconds since 1 January 1970 in
UTC obtained from the signature generator. This approach will prevent
replay attacks by changing the content of the signature each time a
node wants to send a DNS message. The format of DNS messages is
explained in section 4.1.2 RFC 1035 [RFC1035].
+---------------------------------------+
| Algorithm Name |
| |
+---------------------------------------+
| Type |
| |
+---------------------------------------+
| IP tag |
| (16 bytes) |
+---------------------------------------+
| Parameter Len |
| (1 byte) |
+---------------------------------------+
| Parameters |
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| (variable) |
+---------------------------------------+
| Signature Len |
| (1 byte) |
+---------------------------------------+
| Signature |
| (variable) |
+---------------------------------------+
| old pubkey Len |
| (1 byte) |
+---------------------------------------+
| old pubkey |
| (variable) |
+---------------------------------------+
| old Signature Len |
| (1 byte) |
+---------------------------------------+
| old Signature |
| (variable) |
+---------------------------------------+
Figure 4 CGA-TSIG DATA Field
3. Generate old signature
If the nodes generated new key pairs, then they need to add the old
public key and message, signed by the old private key, to CGA-TSIG
DATA. A node will retrieve the timestamp from Time Signed, will use
the old private key to sign it, and then will add the content of this
signature to the old signature field of CGA-TSIG DATA. This step MUST
be skipped when the node did not generate new key pairs.
7. Authentication During Zone Transfer
This section discusses the use of CGA-TSIG for the authentication of
two DNS servers (a master and a slave). In the case of processing a
DNS update for multiple DNS servers (authentication of two DNS
servers), there are two possible scenarios with regard to the
authentication process, which differs from that of the authentication
of a node (client) with one DNS server. This is because of the need
for human intervention.
a. Add the DNS servers' IP address to a slave configuration file
A DNS server administrator should only manually add the IP address of
the master DNS server to the configuration file of the slave DNS
server. When the DNS update message is processed, the slave DNS
server can authenticate the master DNS server based on the source IP
address and then, prove the ownership of this address by use of the
CGA-TSIG option from the TSIG RR. This scenario will be valid until
the IP address in any of these DNS servers changes.
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To automate this step's process, the DNS Update message sender's
public key must be saved on the other DNS server, after the source IP
address has been successfully verified for the first time. In this
case, when the sender generates a new IP address by executing the CGA
algorithm using the same public key, the other DNS server can still
verify it and add its new IP address to the DNS configuration file
automatically.
b. Retrieve public/private keys from a third party Trusted Authority
(TA)
The message exchange option of SeND [RFC3971] may be used for the
retrieval of the third party certificate. This may be done
automatically from the TA by using the Certificate Path Solicitation
and the Certificate Path Advertisement messages. Like in scenario b,
the certificate should be saved on the DNS server for later use for
the generation of its address or for the DNS update process. In this
case, whenever any of these servers want to generate a new IP
address, then the DNS update process can be accomplished
automatically without the need for human intervention.
7.1. Verification process
Sender authentication is necessary in order to prevent attackers from
making unauthorized modifications to DNS servers through the use of
spoofed DNS messages. The verification process executes the following
steps:
1. Execute the CGA verification
These steps are found in section 5 RFC 3972. If the sender of the DNS
message uses another algorithm, instead of CGA, then this step
becomes the verification step for that algorithm. If the verification
process is successful, then step 2 will be executed. Otherwise the
message will be discarded without further action.
2. Check the Time Signed
The Time Signed value is obtained from TSIG RDATA and is called t1.
The current system time is then obtained and converted to UTC time
and is called t2. If t1 is in the range of t2 and t2 minus x minutes
(see formula 1, x minutes may vary according to transmission lag
time) then step 3 will be executed. Otherwise, the message will be
considered a spoofed message and the message should be discarded
without further action. The range is used in consideration of the
delays that can occur during its transmission over TCP or UDP. Both
times must use UTC time in order to avoid differences in time based
on different geographical locations.
t2-x <= t1 <= t2 (1)
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3. Verify the signature
The signature contained in CGA-TSIG DATA should be verified. This can
be done by retrieving the public key and signature from CGA-TSIG DATA
and using this public key to verify the signature. If the
verification process is successful, then step 4 will be executed. If
the verification fails, then the message should be discarded without
further action.
4. Verify the source IP address
The source IP address of the Update requester MUST be checked against
the one contained in the DNS configuration file. If it is the same,
then the Update Message should be processed, otherwise, step 5 will
be executed.
5. Verify the public key
The DNS server checks whether or not the public key retrieved from
CGA-TSIG DATA is the same as what was available in the storage where
the public keys and IP addresses were saved. If no entry is found in
storage for this public key, then the update will be rejected without
further action. Otherwise, when the old public key length is not zero
go to step 6.
6. Verify the old public key
If the old public key length is zero, then skip this step and discard
the DNS update message without further action. If the old public key
length is not zero, then the DNS server will retrieve the old public
key from CGA-TSIG DATA and will check to see whether or not it is the
same as what was saved in the DNS server's storage where the public
keys and IP addresses are stored. If it is the same, then step 6 will
be executed, otherwise the message should be discarded without
further action.
7. Verify the old signature
The old signature contained in CGA-TSIG DATA should be verified. This
can be done by retrieving the old public key and the old signature
from CGA-TSIG DATA and then using this old public key to verify the
old signature. If the verification is successful, then the Update
Message should be processed and the new public key should be replaced
with the old public key in the DNS server. If the verification
process fails, then the message should be discarded without further
action.
8. Authentication During the FQDN or PTR Update
Normally the DHCPv6 server will update the client's RRs on their
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behalf In the scenario where SeND is used as a secure NDP, the nodes
will need to do this process themselves unless there is stateless
DHCPv6 server available. CGA-TSIG can be used To give nodes the
ability of doing this process themselves. In this case the clients
need to include the CGA-TSIG option in order to allow the DNS server
to verify them. The verification process is the same as that
explained in section except for step 4.
8.1. Verification Process
The verification steps are the same as those is explained in section
5.1, but removing step 4 and modifying step 5.
1- Execute the CGA verification
2- Check the Time Signed
3- Verify the signature
4. Verify the public key
The DNS server checks whether or not the public key retrieved from
CGA-TSIG DATA is the same as what was available in the storage where
the public keys and IP addresses were saved. If no entry is found in
storage for this public key, and the FQDN or PTR is also not
available in the DNS server, then the DNS server will store the
public key of this node in his database and add this node's PTR and
FQDN. Otherwise if any PTR is available, and the node IP tag is
empty, or there is currently another public key associated with the
node's FQDN, then the update will be rejected without further action.
Otherwise go to step 5 when the old public key length is not zero.
5- Verify the public key
6- Verify the old public key
7- Verify the old signature
9. Authentication During Query Resolving (stub to recursive)
A DNS query request sent by a host, such as a client or a mail
server, does not need to include CGA-TSIG DATA because the resolver
responds to anonymous queries. But the resolver's response SHOULD
contain the CGA-TSIG DATA field in order to enable this client to
verify him.
In generation of the CGA-TSIG for a resolver, there is no need to
include the IP tag. This is because resolvers don't usually have
several IP addresses so the client does not need to keep several IP
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addresses for the same resolver.
9.1. Verification process
When a resolver responds to the host's query request for the first
time, the client saves its public key in a file. This allows the
client to verify this resolver when it changes its IP address due to
privacy or security concerns. The first 2 steps of the verification
process are the same as those steps explained in section 5.1 These
steps are as follows:
1. Execute the CGA verification
2. Check the Time Signed
3. Verify the Source IP address
If the resolver's source IP address is the same as that which is
known for the host, then step 4 will be executed. Otherwise the
message SHOULD be discarded without further action.
4. Verify the signature
The signature contained in CGA-TSIG DATA should be verified. This can
be done by retrieving the public key and signature from CGA-TSIG DATA
and using this public key to verify the signature. If the
verification process is successful, then step 5 will be executed. If
the verification fails, then the message should be discarded without
further action.
5. Verify the public key
The host checks whether or not the public key retrieved from CGA-TSIG
DATA matches any public key that was previously saved in the storage
where the public keys and IP addresses of resolvers are saved. If
there is a match, then the message is processed. If not, then step 5
will be executed.
5. Verify the old public key
If the old public key length is zero, then skip this step and discard
the DNS query response without further action. If the old public key
length is not zero, then the host will retrieve the old public key
from CGA-TSIG DATA and will check whether or not it is the same as
what was saved in the host's storage where the public keys and IP
addresses are stored. If it is the same, then step 6 will be
executed, otherwise the message should be discarded without further
action.
6. Verify the old signature
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The old signature contained in CGA-TSIG DATA should be verified. This
can be done by retrieving the old public key and old signature from
CGA-TSIG DATA and then using this old public key to verify the old
signature. If the verification is successful, then the DNS Message
should be processed and the new public key should be replaced with
the old public key of the resolver in the host. If the verification
process fails, then the message should be discarded without further
action.
10. Authentication During Query Resolving (Auth. to recursive)
This verification step in the authentication of authoritative to
recursive DNS server is the same as that explained in section 7.1. In
this case the recursive DNS server does not need to include CGA-TSIG,
but the root DNS server does need to include it in order to enable
the recursive DNS server to verify it.
11. No cache parameters available or SeND is not supported
In the case where there are no cache parameters available during the
IP address generation, there are then two scenarios that come into
play here. In the first scenario there is the case where the sender
of a DNS message needs to generate a key pair and generate the
CGA-TSIG data structure as explained in section 4. The node SHOULD
skip the first section of the verification processes explained in
section 5.1 , section 6.1 and section 7.1.
In the second scenario, as explained in section 4.2 (step 1), it is
not necessary for the server to support the SeND or CGA algorithm.
The DNS administrator can make a one time use of a CGA script to
generate the CGA parameters and then manually configure the IP
address of this DNS server. Then later, this DNS server can use those
values as a means for authenticating other nodes. The verifier nodes
also do not necessarily need to support SeND. They only need to
support CGA-TSIG.
12. Security Considerations
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The approach explained in this draft, CGA-TSIG, is a solution for
securing DNS messages from spoofing type attacks like those explained
in section 3.
A problem that may arise here concerns attacks against the CGA
algorithm. In this section we will explain the possibility of such
attacks against CGA [5] and explain the available solutions that we
considered in this draft.
a) Discover an Alternative Key Pair Hashing of the Victim's Node
Address
In this case an attacker would have to find an alternate key pair
hashing of the victim?s address. The probability for success of this
type of attack will rely on the security properties of the underlying
hash function, i.e., an attacker will need to break the second
pre-image resistance of that hash function. The attacker will perform
a second pre-image attack on a specific address in order to match
other CGA parameters using Hash1 and Hash2. The cost of doing this is
(2^59+1) * 2^(16*1). If the user uses a sufficient security level, it
will be not feasible for an attacker to carry out this type of attack
due to the cost involved. Changing the IP address frequently will
also decrease the chance for this type of attack succeeding.
b) DoS to Kill a CGA Node
Sending a valid or invalid CGA signed message with high frequency
across the network can keep the destination node(s) busy with the
verification process. This type of DoS attack is not specific to CGA,
but it can be applied to any request-response protocol. One possible
solution ,to mitigate this attack, is to add a controller to the
verifier side of the process to determine how many messages a node
has received over a certain period of time from a specific node. If a
determined threshold rate is exceeded, then the node will stop
further receipt of incoming messages from that node.
c) CGA Privacy Implication
Due to the high computational complexity necessary for the creation
of a CGA, it is likely that once a node generates an acceptable CGA
it will continue its use at that subnet. The result is that nodes
using CGAs are still susceptible to privacy related attacks. One
solution to these types of attacks is setting a lifetime for the
address as explained in RFC 4941.
13. IANA Considerations
The IANA has allowed for choosing new algorithm(s) for use in the
TSIG Algorithm name. Algorithm name refers to the algorithm described
in this document. The requirement to have this name registered with
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IANA is specified.
In section 4.1, Type should allow for the use of future optional
algorithms with regard to SeND. The default value for CGA might be 1.
Other algorithms would be assigned a new number sequentially. For
example, a new algorithm called SSAS [4,5] could be assigned a value
of 2.
14. Appendix
- A sample key storage for CGA-TSIG
create table cgatsigkeys (
id INT auto_increment,
pubkey VARCHAR(300),
primary key(id)
);
create table cgatsigips (
id INT auto_increment,
idkey INT,
IP VARCHAR(20),
FOREIGN KEY (idkey) REFERENCES cgatsigkeys(id)
primary key(id)
);
CGA-TSIG tables on mysql backend database
- a sample format of stored parameters in the node
For example, the modifier is stored as bytes and each byte might be
separated by a comma (for example : 284,25,14,...). Algorithmtype is
the algorithm used in signing the message. Zero is the default
algorithm for RSA. Secval is the CGA Sec value that is, by default,
one. GIP is the global IP address of this node (for example:
2001:abc:def:1234:567:89a). oGIP is the old IP address of this node,
before the generation of the new IP address. Keys contains the path
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where the CGA-TSIG algorithm can find the PEM format used for the
public/private keys (for example: /home/myuser/keys.pem ).
<?xml version="1.0" encoding="UTF-8"?>
<Details>
<CGATSIG>
<modifier value=""/>
<algorithmtype value="0"/>
<secval value="1"/>
<GIP value=""/>
<oGIP value=""/>
<Keys value=""/>
</CGATSIG>
</Details>
XML file contains the cached DATA
15. Acknowledgements
The author would like to thank all those people who directly helped
in improving this draft and all supporters of this draft, especially
Ralph Droms, Andrew Sullivan, Ted Lemon, Brian Haberman.
16. References
16.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3972] Aura, T., "Cryptographically Generated Addresses
(CGA)," RFC 3972, March 2005.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
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INTERNET DRAFT TSIG using CGA in IPv6 September 27, 2013
[RFC2930] Eastlake 3rd, D., "Secret Key Establishment for
DNS (TKEY RR)", RFC 2930, September 2000.
[RFC1035] Mockapetris, P., "Domain Names - Implementation
And Specification", RFC 1035, November 1987.
[RFC4941] Narten, T., Draves, R., Krishnan, S., "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC2136] Vixie, P. (Editor), Thomson, S., Rekhter, Y.,
Bound, J., "Dynamic Updates in the Domain Name System (DNS
UPDATE)", RFC 2136, April 1997.
[RFC2845] Vixie, P., Gudmundsson, O. , Eastlake 3rd, D.,
Wellington, B., " Secret Key Transaction Authentication for
DNS (TSIG)", RFC 2845, May 2000.
16.2. Informative References
[1] Aura, T., "Cryptographically Generated Addresses (CGA)",
Lecture Notes in Computer Science, Springer, vol. 2851/2003, pp.
29-43, 2003.
[2] Montenegro, G. and Castelluccia, C., "Statistically Unique
and Cryptographically Verifiable (SUCV) Identifiers and
Addresses," ISOC Symposium on Network and Distributed System
Security (NDSS 2002), the Internet Society, 2002.
[3] AlSa'deh, A., Rafiee, H., Meinel, C., "IPv6 Stateless Address
Autoconfiguration: Balancing Between Security, Privacy and
Usability". Lecture Notes in Computer Science, Springer(5th
International Symposium on Foundations & Practice of Security
(FPS). October 25 - 26, 2012 Montreal, QC, Canada), 2012.
[4] Rafiee, H., Meinel, C., "A Simple Secure Addressing
Generation Scheme for IPv6 AutoConfiguration (SSAS)". Work in
progress, http://tools.ietf.org/html/draft-rafiee-6man-ssas,
2013.
[5] Rafiee, H., Meinel, C., "A Simple Secure Addressing Scheme
for IPv6 AutoConfiguration (SSAS)", 11th International conference
on Privacy, Security and Trust (IEEE PST), 2013.
[6] AlSa'deh, A., Rafiee, H., Meinel, C., "Cryptographically
Generated Addresses (CGAs): Possible Attacks and Proposed
Mitigation Approaches," in proceedings of 12th IEEE International
Conference on Computer and Information Technology (IEEE CIT'12),
pp.332-339, 2012.
[7] Rafiee, H., Meinel, C., "A Secure, Flexible Framework for DNS
Authentication in IPv6 Autoconfiguration" in proceedings of The
12th IEEE International Symposium on Network Computing and
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Applications (IEEE NCA13), 2013.
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Authors' Addresses
Hosnieh Rafiee
Hasso-Plattner-Institute
Prof.-Dr.-Helmert-Str. 2-3
Potsdam, Germany
Phone: +49 (0)331-5509-546
Email: ietf@rozanak.com
Dr. Christoph Meinel
(Professor)
Hasso-Plattner-Institute
Prof.-Dr.-Helmert-Str. 2-3
Potsdam, Germany
Email: meinel@hpi.uni-potsdam.de
Dr. Martin von Loewis
(Professor)
Hasso-Plattner-Institute
Prof.-Dr.-Helmert-Str. 2-3
Potsdam, Germany
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