One document matched: draft-rafiee-intarea-cga-tsig-07.txt
Differences from draft-rafiee-intarea-cga-tsig-06.txt
DNS Extensions H. Rafiee
INTERNET-DRAFT Ciber AG
Updates RFC 2845 (if approved) M. v. Loewis
Intended Status: Standards Track C. Meinel
Hasso Plattner Institute
Expires: August 15, 2014 February 15, 2014
Secure DNS Authentication using CGA/SSAS Algorithm in IPv6
<draft-rafiee-intarea-cga-tsig-07.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. This document also introduces a possible
algorithm for DNS data confidentiality.
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 August 15, 2014.
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Copyright Notice
Copyright (c) 2014 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 . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 4
2. Conventions used in this document . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Algorithm overview . . . . . . . . . . . . . . . . . . . . . 7
4.1. The CGA-TSIG DATA structure . . . . . . . . . . . . . . 7
4.2. Generation of CGA-TSIG DATA . . . . . . . . . . . . . . . 9
5. Authentication during Zone Transfer . . . . . . . . . . . . . 12
5.1. Verification process . . . . . . . . . . . . . . . . . . 13
6. Authentication during the FQDN or PTR Update . . . . . . . . 14
6.1. Verification Process . . . . . . . . . . . . . . . . . . 15
7. Authentication during Query Resolving (stub to recursive) . . 15
7.1. Verification process . . . . . . . . . . . . . . . . . . 15
8. Authentication during Query Resolving (Auth. to recursive) . 17
9. No cache parameters available or SeND is not supported . . . 17
10. How to obtain the IP address of resolvers . . . . . . . . . 17
11. CGA-TSIG Data confidentiality . . . . . . . . . . . . . . . 17
11.1. Generation of secret key . . . . . . . . . . . . . . . . 18
11.2. DNS message generation . . . . . . . . . . . . . . . . . 18
11.3. CGA-TSIGe DATA generation . . . . . . . . . . . . . . . 18
11.4. Process of encrypted DNS message . . . . . . . . . . . . 18
12. CGA-TSIG/CGA-TSIGe Applications . . . . . . . . . . . . . . 19
12.1. IP Spoofing . . . . . . . . . . . . . . . . . . . . . . 20
12.2. DNS Dynamic Update Spoofing . . . . . . . . . . . . . . 20
12.3. Resolver Configuration Attack . . . . . . . . . . . . . 20
12.4. Exposing Shared Secret . . . . . . . . . . . . . . . . . 20
12.5. Replay attack . . . . . . . . . . . . . . . . . . . . . 20
12.6. Data confidentiality . . . . . . . . . . . . . . . . . . 21
13. Security Considerations . . . . . . . . . . . . . . . . . . . 21
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
15. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . 22
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16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
17.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 24
17.2. Informative . . . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
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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.
But, handling this shared secret in a secure manner and exchanging
it, does not seem to be easy. This is especially true if the IP
addresses are dynamic due to privacy reasons or the shared secret is
exposed to attacker. To address the existing problems with TSIG, this
document proposes the use of Cryptographically Generated Addresses
(CGA) [RFC3972] or Secure Simple Addressing Scheme for IPv6
Authoconfiguration (SSAS) 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?s public key and its IP address without the need for
the introduction of a new infrastructure.
This document also addresses the DNS data confidentiality by using
both asymmetric and symmetric cryptography as well as data integrity.
This document updates the following sections in TSIG document
- section 4.2: The server MUST not generate a signed response to an
unsigned request => The server MUST not generate a signed response to
an unsigned request, unless the Algorithm Name filed contains
CGA-TSIG.
- Section 4.5.2: It MUST include the client's current time in the
time signed field, the server's current time (a u_int48_t) in the
other data field, and 6 in the other data length field => It MUST
include the client's current time in the time signed field, the
server's current time (a u_int48_t) in the other data field, and if
the Algorithm Name is CGA-TSIG, then add the length of this client?s
current time to the total length of Other DATA field. The client?s
current time in this case will be placed after the CGA-TSIG Data.
1.1. 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
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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, 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. The
public key verification in DNSSEC creates chicken and eggs situation.
In other words, the key for verifying messages should be obtained
from DNSSEC server itself. This is why the query requestor needed to
ask other DNS servers up to top level in root to be able to verify
the key. If this does not happen, DNSSEC is vulnerable to IP spoofing
attack. This problem could easily be handled by the use of CGA-TSIG
as a means of providing the proof of IP address ownership.
If TSIG is in use, 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).
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"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.
=> This sign in the document should be interpreted as "change to".
3. Terminology
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.
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- 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
4. 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).
4.1. 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 1
and 2). The DNS RRTYPE MUST be set to TSIG [RFC2845]. The RDATA
Algorithm Name MUST be set to CGA-TSIG. The Name MUST be set to root
(.).This is the smallest possible value that can be used. The MAC
Size MUST be set to 0. 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 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 |
| |
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+---------------------------------------+
| Mac |
| |
+---------------------------------------+
| Original ID |
| |
+---------------------------------------+
| Error |
| |
+---------------------------------------+
| OTHER LEN |
| |
+---------------------------------------+
| OTHER DATA |
| |
+---------------------------------------+
Figure 1 Modified TSIG RDATA
The CGA-TSIG DATA Field and the CGA-TSIG Len will occupy the first
two slots of Other DATA. Figure 2 shows the layout. Any extra
options/data should be placed after CGA-TSIG field. CGA-TSIG Len is
the length of CGA-TSIG DATA in byte. This value is multiple of 8.
+---------------------------------------+
| CGA-TSIG Len |
| (1 byte) |
+---------------------------------------+
| CGA-TSIG DATA |
| |
+---------------------------------------+
| Other Options |
| |
+---------------------------------------+
Figure 2 Other DATA section of RDATA field
CGA-TSIG DATA Field Name Data Type Notes
--------------------------------------------------------------
Algorithm type u_int16_t IANA numeric value of
the algorithm
for RSA 1.2.840.113549.1.1.1
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
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field
old pubkey variable Old public key in ASN.1 DER
format (the same format as 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 (An Interface ID is the 64 leftmost bits of an IPv6 address.).
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 zeroes. 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.
4.2. Generation of CGA-TSIG DATA
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, collision count and public key from cache. It concatenates
the old IP address with the CGA parameters, i.e., modifier, subnet
prefix, collision count, public key (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.
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Note: If the node is a DNS server (resolver or authoritative DNS
server) which does not support SeND, but wants to use CGA-TSIG
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.
+---------------------------------------+
| Algorithm Name |
| |
+---------------------------------------+
| Type |
| |
+---------------------------------------+
| IP tag |
| (16 bytes) |
+---------------------------------------+
| Parameter Len |
| (1 byte) |
+---------------------------------------+
| Parameters |
| (variable) |
+---------------------------------------+
| Signature Len |
| (1 byte) |
+---------------------------------------+
| Signature |
| (variable) |
+---------------------------------------+
| old pubkey Len |
| (1 byte) |
+---------------------------------------+
| old pubkey |
| (variable) |
+---------------------------------------+
| old Signature Len |
| (1 byte) |
+---------------------------------------+
| old Signature |
| (variable) |
+---------------------------------------+
Figure 3 CGA-TSIG DATA Field
2. Generate signature
For signature generation, The 128-bit CGA Message Type tag value for
SeND that is 0x086F CA5E 10B2 00C9 9C8C E001 6427 7C08, is
concatenated with the whole DNS message from Type to additional data
sections (Please refer to figure 4 and figure 5) excluding the
signature fields itself in the CGA-TSIG DATA is signed by using a RSA
algorithm, by default, or any future algorithm used in place of RSA,
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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 4.1.3 RFC 1035 [RFC1035]. Figure 6 shows this signature.
+-----+------+--------+
|Type |Length|Reserved|
|1byte|1 byte| 1 byte |
+---------------------+
| Header |
| 12 bytes |
+---------------------+
| Zone section |
| variable length |
+---------------------+
| prerequisite |
| variable length |
+---------------------+
| Update section |
| variable length |
+---------------------+
| Additional Data |
| variable length |
+---------------------+
Figure 4 DNS update message
+-----+------+--------+
|Type |Length|Reserved|
|1byte|1 byte| 1 byte |
+---------------------+
| Header |
| 12 bytes |
+---------------------+
| Question |
| variable length |
+---------------------+
| Answer |
| variable length |
+---------------------+
| Authority |
| variable length |
+---------------------+
| Additional Data |
| variable length |
+---------------------+
Figure 5 DNS Query message (section 4.1 RFC 1035)
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+------------------+
| CGA message tag |
| 16 bytes |
+------------------+
| DNS message |
| (excluding |
| signature fields |
|in CGA-TSIG DATA) |
+------------------+
Figure 6 CGA-TSIG Signature content
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.
5. 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.
To automate this process, the sender's public key of the DNS Update
message 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.
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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.
5.1. 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. 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 2 will be executed. If
the verification fails, then the message should 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. Fudge time is obtained from TSIG RDATA. If t1 is in
the range of t2 and t2 minus/plus fudge (see formula 1) 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.
(t1 - fudge) <= t2 <=(t1 + fudge) (1)
3. 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 4 will be executed. Otherwise the
message will be discarded without further action.
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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.
6. Authentication during the FQDN or PTR Update
Normally the DHCPv6 server will update the client's RRs on their
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.
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6.1. 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- Verify the signature
2- Check the Time Signed
3- Execute the CGA verification
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
7. 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 generate 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. However, the client needs to include the TSIG RDATA and
set the Algorithm type to CGA-TSIG. It MUST set the CGA-TSIG Len to
zero. This allows the resolver to know when to include CGA-TSIG for
verification process in client.
In generation of the CGA-TSIG for a resolver, there is no need to
include the IP tag. This is because resolvers do not usually have
several IP addresses so the client does not need to keep several IP
addresses for the same resolver.
7.1. Verification process
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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 steps 2 and 3 of the verification
process are the same as those steps explained in section 5.1. These
steps are as follows:
1. 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 2 will be executed. If
the verification fails, then the message should be discarded without
further action.
2. Check the Time Signed
3. Execute the CGA verification
4. 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 5 will be executed. Otherwise 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
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
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process fails, then the message should be discarded without further
action.
8. 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 generate CGA-TSIG
DATA, but the root DNS server does need to include it in order to
enable the recursive DNS server to verify it. The recursive DNS
server needs to include the TSIG RDATA and set the Algorithm type to
CGA-TSIG. It MUST set the CGA-TSIG Len to zero. This allows the root
DNS server to know when to include CGA-TSIG for verification process
in client.
9. 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.
10. How to obtain the IP address of resolvers
Nodes can obtain the IP address of resolvers from the DHCPv6 server
(that will not be secure) or from a DNS option of Router
Advertisement message [RFC6106] after authenticating the router via a
trusted authority. The IP addresses can be generated using CGA, SSAS
or other mechanisms.
11. CGA-TSIG Data confidentiality
One possible solution to provide the DNS server with data
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confidentiality during DNS update or other DNS query processes is the
use of symmetric encryption with CGA-TSIG that is called CGA-TSIGe.
In this case, the node MUST set the Algorithm type in TSIG RDATA to
CGA-TSIGe.
11.1. Generation of secret key
To encrypt the DNS message using a symmetric algorithm for
performance purposes, first, a node needs to retrieve the public key
of the DNS server. It is possible to use the current DNSKEY RR (RFC
3757) to send the public key of the DNS server. When the client wants
to update any records on the DNS server, it first sends a DNS message
and asks for the public key of the DNS server. DNS server then
answers to this query and includes the public key contained in the
DNSKEY RR with the SEP flag set to zero. This is done to indicate
that it is not the zone key. The DNS server SHOULD include CGA-TSIG
DATA so that the client can verify its IP address. In this case,
there will be a binding between DNS server?s public key and its IP
address. After a successful verification, the node then generates a
16 byte random number and calls it a secret key. It encrypts this
secret key using the DNS server public key. This allows only the DNS
server to decrypt this secret key. In this case, the node sets the
MAC in TSIG RDATA to the digest of secret key and set the MAC Size to
the length of this digest. The DNS server knows what to do with MAC
field from the Algorithm type in TSIG. If it is CGA-TSIGe, then it
looks for an encrypted secret key.
11.2. DNS message generation
The node MUST encrypt all DNS message sections that required
protections using the secret key generated in last section and AES
symmetric algorithm. It excludes TSIG RDATA (That usually added in
the additional section of the DNS messages) from the encryption text.
They are explained in figure 4 and figure 5 of section 4.2 of this
document.
11.3. CGA-TSIGe DATA generation
The CGA-TSIGe generation is the same as that explained in section 4.2
of this document. But only the Algorithm type MUST be set to
CGA-TSIGe.
11.4. Process of encrypted DNS message
When the DNS server receives the message from any node with TSIG
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RDATA Algorithm type set to CGA-TSIGe, it execute the following
steps:
1- Retrieve the secret key
The DNS server retrieves the secret key from MAC field. It then
decrypts this secret key using its own private key.
2- Decrypt the DNS message
The DNS server decrypts the DNS server message using this secret key
and the symmetric algorithm, which by default is AES.
Then the DNS server can starts the verification process as explained
in section 5.1, 6.1, 7.1 of this document.
12. CGA-TSIG/CGA-TSIGe Applications
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
scenarios. 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 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.
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12.1. 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.
12.2. 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
validity of the update message.
12.3. 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.
12.4. 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.
12.5. 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.
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12.6. Data confidentiality
Encrypting the whole DNS message will avoid the attacker to know the
content of DNS messages. This will avoid zone walking and many other
attacks on DNS RRs. This also provides the higher privacy for hosts
that has DNS records.
13. Security Considerations
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
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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.
14. 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
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.
IANA also needs to define a numeric algorithm number for ECC. The
similar way that is defined for RSA.
15. Appendix
- A sample key storage for CGA-TSIG
create table cgatsigkeys (
id INT auto_increment,
pubkey VARCHAR(300),
primary key(id)
);
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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
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="1.2.840.113549.1.1.1"/>
<secval value="1"/>
<GIP value=""/>
<oGIP value=""/>
<Keys value=""/>
</CGATSIG>
</Details>
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XML file contains the cached DATA
16. Acknowledgements
The continual improvement of this document is as a result of the
helps and assistance of its supporters.
The authors 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. The authors
would like also to special acknowledge the supports of NLnet Labs
director and researchers; Olaf Kolkman, Matthijs Mekking and their
master student Marc Buijsman.
17. References
17.1. 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.
[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.
[RFC6106] Jeong, J., Park, S., Beloeil, L., Madanapalli,
S.,"IPv6 Router Advertisement Options for DNS
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Configuration",RFC 6106, November 2010.
17.2. 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
Applications (IEEE NCA13), 2013.
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Authors' Addresses
Hosnieh Rafiee
Ciber AG
KoelnTurm
Im Mediapark 8
50670, Cologne
http://www.ciber.com
Phone: +49 (0221) 272 67- 122
Email: ietf@rozanak.com
Christoph Meinel
Hasso-Plattner-Institute
Prof.-Dr.-Helmert-Str. 2-3
Potsdam, Germany
Email: meinel@hpi.uni-potsdam.de
Martin von Loewis
Hasso-Plattner-Institute
Prof.-Dr.-Helmert-Str. 2-3
Potsdam, Germany
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