Internet DRAFT - draft-ietf-bfd-generic-crypto-auth
draft-ietf-bfd-generic-crypto-auth
Network Working Group M. Bhatia
Internet-Draft Alcatel-Lucent
Intended status: Standards Track V. Manral
Expires: October 19, 2014 Hewlett-Packard Co.
D. Zhang
Huawei
M. Jethanandani
Ciena Corporation
April 17, 2014
BFD Generic Cryptographic Authentication
draft-ietf-bfd-generic-crypto-auth-06
Abstract
This document proposes an extension to Bidirectional Forwarding
Detection (BFD) to allow the use of arbitrary cryptographic
authentication algorithms in addition to the already-documented
authentication schemes described in the base specification. This
document adds the basic infrastructure that is required for
supporting algorithm and key agility for BFD.
Requirements Language
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].
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 October 19, 2014.
Bhatia , et al. Expires October 19, 2014 [Page 1]
Internet-Draft BFD Generic Authentication April 2014
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. BFD Security Association . . . . . . . . . . . . . . . . . . 4
3. Authentication Procedures . . . . . . . . . . . . . . . . . . 5
3.1. Authentication Types . . . . . . . . . . . . . . . . . . 5
3.2. Authentication Section Format . . . . . . . . . . . . . . 5
3.3. Procedures at the Sending Side . . . . . . . . . . . . . 6
3.4. Procedure at the Receiving Side . . . . . . . . . . . . . 7
3.5. Key Selection for BFD Packet Transmission . . . . . . . . 8
3.6. Replay Protection using Extended Sequence Numbers . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
The base specification of Bidirectional Forwarding Detection
[RFC5880] defines five authentication schemes: Simple Password, Keyed
MD5, Meticulous Keyed MD5, Keyed SHA-1, and Meticulous SHA-1. In
Simple Password, passwords are transferred in plain text. An
attacker with physical access to the network can easily eavesdrop on
the password and compromise the security of the BFD packet exchanges.
In Keyed MD5 and Meticulous Keyed MD5, the BFD devices on the both
sides of a BFD session share a secret key which is used to generate a
keyed MD5 digest for each packet, and a monotonically increasing
sequence number scheme is used to prevent replay attacks. Keyed
SHA-1 and Meticulous SHA-1 modes are similar to MD5, and it uses
SHA-1 instead of MD5 to generate a digest for each packet.
Bhatia , et al. Expires October 19, 2014 [Page 2]
Internet-Draft BFD Generic Authentication April 2014
The security strength of the cryptographic algorithms adopted in the
authentication schemes are relatively weak. Both the MD5 algorithm
and the SHA-1 algorithm are known to be vulnerable to collision
attacks. In MD5-attack [MD5-attack] and Dobb96a [Dobb96a], Dobb96b
[Dobb96b], several methods of generating hash collisions for some
applications of MD5 are proposed. Similar security vulnerabilities
of SHA-1 are introduced in SHA-1-attack1 [SHA-1-attack1] and
SHA-1-attack2 [SHA-1-attack2]. It is therefore desired that BFD must
support newer algorithms that have not yet been broken.
Additionally, the transition mechanism from one algorithm to the
other must be seamless.
The other issue with the existing authentication schemes is the
vulnerability to replay attacks. In non-meticulous authentication
schemes, sequence numbers are only increased occasionally. This
behavior can be taken advantage of by an attacker to perform intra-
session replay attacks. In meticulous authentication schemes,
sequence numbers are required to monotonically increase with each
successive packet, which eliminates the possibility of intra-session
replay attacks.
BFD session timers are often defined with the granularity of
microseconds. Although in practice BFD devices send packets at
millisecond intervals, they can potentially send packets at a much
higher rate. Since the cryptographic sequence number space is only
32 bits, when using Meticulous Authentication, a sequence number used
in a BFD session can reach its maximum value and roll over within a
short period. For instance, if the value of a sequence number is
increased by one every millisecond, then it will reach its maximum in
less than 8 weeks. This can potentially be exploited to launch
inter-session replay attacks.
In order to address the issues mentioned above, this document
proposes two new authentication types that can be used to secure the
BFD packets. The two authentication types are - Cryptographic
Authentication (CRYPTO_AUTH) and Meticulous Cryptographic
Authentication (MET_ CRYPTO_AUTH). Unlike earlier authentication
types that were defined in BFD, the proposed authentication types are
not tied to any particular authentication algorithm or construct.
These can use different authentication algorithms and constructs like
MD5, SHA-1, SHA-2, HMAC-SHA1, HMAC-SHA2, etc. to provide
authentication and data integrity protection for BFD control packets.
The packet replay mechanism has also been enhanced to improve its
capability in handling inter and intra-session replay attacks.
It should be noted that this document attempts to fix the security
issues raised by the manual key management procedure that currently
Bhatia , et al. Expires October 19, 2014 [Page 3]
Internet-Draft BFD Generic Authentication April 2014
exists within BFD, as part of the Phase One described in KARP Design
Guidelines [RFC6518]. Therefore, only the pre-shared keys is
considered in this document. However, the solution described in this
document is generic and does not preclude the possibility of
supporting keys derived from an automated key management protocol.
2. BFD Security Association
The BFD protocol does not include an in-band mechanism to create or
manage BFD Security Associations (BFD SA). A BFD SA contains a set
of shared parameters between any two legitimate BFD devices.
The parameters associated with a BFD SA are listed as follows:
o Authentication Algorithm : This indicates the authentication
algorithm to be used with the BFD SA. This information SHOULD
never be sent in plain text over the wire.
o Authentication Key : This indicates the cryptographic key
associated with this BFD SA. The length of this key is variable
and depends upon the authentication algorithm specified by the BFD
SA. Operators MUST ensure that this is never sent over the
network in clear-text via any protocol. Care should also be taken
to ensure that the selected key is unpredictable, avoiding any
keys known to be weak for the algorithm in use. Randomness
Requirements for Security [RFC4086] contains helpful information
on both key generation techniques and cryptographic randomness.
o Authentication Key Identifier (Key ID) : This is a two octet
unsigned integer used to uniquely identify the BFD SA. This ID
could be manually configured by the network operator (or, in the
future, possibly by some key management protocol specified by the
IETF). The receiver determines the active SA by looking at this
field in the incoming packet. The sender puts this Key ID in the
BFD packet based on the active configuration. Using Key IDs makes
changing keys while maintaining protocol operation convenient.
Normally, an implementation would allow the network operator to
configure a set of keys in a key chain, with each key in the chain
having fixed lifetime. The actual operation of these mechanisms
is outside the scope of this document. A key ID indicates a tuple
of an authentication key and an associated authentication
algorithm. If a key is expected to be applied with different
algorithms, different Key IDs must be used to identify the
associations of the key with its authentication algorithms
respectively. However, the application of a key for different
purposes must be very careful, since it may make an adversary
easier to collect more material to compromise the key.
Bhatia , et al. Expires October 19, 2014 [Page 4]
Internet-Draft BFD Generic Authentication April 2014
o Not Before Time : The time point before which the key should not
be used.
o Not After Time : The time point after which the key should not be
used.
3. Authentication Procedures
In the proposed authentication extension, an optional authentication
section (Generic Authentication Section) and two authentication types
(Generic Cryptographic Authentication and Generic Meticulous
Cryptographic Authentication) are specified.
3.1. Authentication Types
The Authentication section is only present in a BFD packet if the
Authentication Present (A) bit is set in the packet header. The Auth
Type in the Authentication section is set to TBD1 when Generic
Cryptographic Authentication is in use, while it is set to TBD2 when
Generic Meticulous Cryptographic Authentication is in use.
Both the authentication types use a monotonically increasing sequence
number to protect the BFD session against reply attacks. The only
difference between the two types is that the sequence number is
occasionally incremented in the Cryptographic Authentication mode, as
against the Meticulous Cryptographic Authentication mode, where it is
incremented on every packet.
As a result of this, in the Cryptographic Authentication scheme, a
replay attack is possible till the next sequence number is sent out.
3.2. Authentication Section Format
A new authentication type, TBD1 or TBD2, indicating the generic
cryptographic authentication mechanism in use, is inserted in the
first octet of Authentication Section of the BFD control packet.
For a BFD packet, if the Authentication Present (A) bit is set in the
header and the Authentication Type field is TBD1 (Generic
Cryptographic Authentication) or TBD2 (Generic Meticulous
Cryptographic Authentication), the Authentication Section has the
following format:
Bhatia , et al. Expires October 19, 2014 [Page 5]
Internet-Draft BFD Generic Authentication April 2014
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Auth Type | Auth Len | Auth Key ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number (High Order 32 Bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number (Low Order 32 Bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authentication Data (Variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Auth Type: The Authentication Type, which in this case is TBD1
(Cryptographic Authentication) or TBD2 (Meticulous Cryptographic
Authentication).
o Auth Len: The length of the Authentication Section.
o Auth Key ID: The Key ID of the authentication key used for this
packet, enabling multiple keys to be active simultaneously.
o Sequence Number: A 64-bit sequence number that is used to prevent
replay attacks. For Cryptographic Authentication this value is
incremented occasionally. For Meticulous Cryptographic
Authentication, this value is incremented for each successive
packet transmitted for a session.
o Authentication Data: This field carries the digest computed by
whatever Cryptographic Authentication algorithm is being used to
authenticate the BFD control packet.
3.3. Procedures at the Sending Side
Before a BFD device sends a BFD packet out, the device needs to
select an appropriate BFD SA from its local key database if a keyed
digest for the packet is required. If no appropriate SA is
available, the BFD packet MUST be discarded.
If an appropriate SA is available, the device then derives the key
and the associated authentication algorithm from the SA.
The device sets the Authentication Present (A) bit in the packet
header.
Bhatia , et al. Expires October 19, 2014 [Page 6]
Internet-Draft BFD Generic Authentication April 2014
The device MUST fill the Auth Type, the Auth Len fields and the
Sequence Number field to bfd.XmitAuthSeq before the authentication
data is computed.
The Auth Len field in the Authentication section is set as per the
authentication algorithm that is being used.
The Key ID field is filled.
The computation of the digest is performed. The computing process
can be various when different algorithms are adopted and is out of
the scope of this document.
The generated digest is placed in the Authentication Data field.
3.4. Procedure at the Receiving Side
When a BFD Control packet is received, the following procedure MUST
be followed, in the order specified.
If the Authentication Present (A) bit is set in the packet header and
the Auth Type is TBD1 or TBD2, the receiver is to find an appropriate
BFD SA in its local key table to process the packet. The BFD SA is
identified by the Key ID field in the Authentication Section of the
incoming BFD packet.
If the Auth Key ID field does not match the ID of any configured
authentication key or the associated key is not in its valid period,
the received packet MUST be discarded.
If bfd.AuthSeqKnown is 1, examine the Sequence Number field. For
Cryptographic Authentication, if the Sequence Number lies outside of
the range of bfd.RcvAuthSeq to bfd.RcvAuthSeq+(3*Detect Mult)
inclusive (when treated as an unsigned 64 bit circular number space),
the received packet MUST be discarded. For Meticulous Cryptographic
Authentication, if the Sequence Number lies outside of the range of
bfd.RcvAuthSeq+1 to bfd.RcvAuthSeq+(3*Detect Mult) inclusive (when
treated as an unsigned 64 bit circular number space, the received
packet MUST be discarded.
The device then prepares for generating a digest of the packet.
First of all, the authentication data in the Authentication Value
field needs to be saved somewhere else. Then the Authentication
Value field is set with a pre-specified value (which may be various
in different security algorithms) according the authentication
algorithm indicated in the SA. After this, the device starts
performing the digest generating operations. The work of defining
Bhatia , et al. Expires October 19, 2014 [Page 7]
Internet-Draft BFD Generic Authentication April 2014
actual digest generating operations is out of the scope of this
document.
The calculated data is compared with the received authentication data
in the packet and the packet MUST be discarded if the two do not
match. In such a case, an error event SHOULD be logged.
An implementation MAY have a transition mode where it includes
CRYPTO_AUTH or the MET_CRYPTO_AUTH information in the packets but
does not verify this information. This is provided as a transition
aid for networks in the process of migrating to the new CRYPTO_AUTH
and MET_CRYPTO_AUTH based authentication schemes.
3.5. Key Selection for BFD Packet Transmission
In [I-D.ietf-karp-crypto-key-table], a conceptual key database called
"key table" is introduced. A key table is located in the middle of
key management protocols and security protocols so that a security
protocol can derive long-term keys from the key table but does not
have to know the details of key management. This section describes
how the proposed security solution selects long-lived keys from key
tables [I-D.ietf-karp-crypto-key-table].
Assume that a device R1 tries to send a unicast BFD packet from its
interface I1 to the interface R2 of a remote device R2 at time T.
Because the key should be shared by the by both R1 and R2 to protect
the communication between I1 and I2, R1 needs to provide a protocol
("BFD"), an interface identifier (I1) and a peer identifier (R2) into
the key selection function. Any key that satisfies the following
conditions may be selected:
o The Peer field includes the device ID of R2.
o The Protocol field matches "BFD"
o The PeerKeyName field is not "unknown".
o The Interface field includes I1 or "all".
o The Direction field is either "out" or "both".
o SendNotBefore <= current time <= SendNotAfter.
After a set of keys are provided, a BFD implementation should support
selection of keys based on algorithm preference.
Upon reception of a BFD packet from R1, R2 provides the protocol
("BFD"), the peer identifier (R1), the key identifier derived from
Bhatia , et al. Expires October 19, 2014 [Page 8]
Internet-Draft BFD Generic Authentication April 2014
the incoming packet (L), and the interface (I2) to the key table.
Any key that satisfies the following conditions may be selected:
o The Peer field includes the device ID of R1.
o The Protocol field matches "BFD"
o The LocalKeyName is L
o The Interface field includes I2 or "all".
o The Direction field is either "out" or "both".
o SendNotBefore <= current time <= SendNotAfter.
3.6. Replay Protection using Extended Sequence Numbers
As described in Section 1, if the BFD packets in a session are
transferred with a high frequency, a 32-bit sequence number may reach
its maximum and have to roll back before the session finishes. A
attacker thus can replay the packets intercepted before the sequence
number wrapped without being detected. To address this problem, the
length of the sequence number in the proposed authentication section
has been extended to 64 bits. After the extension, the sequence
number space of a device will not be exhausted for half of a million
years even if the device sends out a BFD packet in every micro-
second. Therefore, the replay attack risks caused by the limited
sequence number space can be largely addressed. However, in Generic
Cryptographic Authentication, the sequence number is only required to
increase occasionally. Therefore, a replayed packet may be regarded
as a legal one until the packet with a larger sequence number is
received. This type of intra-session replay attack cannot be
addressed only by extending the length of sequence numbers.
An anti-replay solution for BFD also needs to consider the scenarios
where a BFD device loses its prior sequence number state (e.g.,
system crash, loss of power). In such cases, a BFD device has to re-
initialize its sequence number. Otherwise, an attacker may be able
to replay a previously intercepted without being detected.
To address this problem, in the proposed solution, the most
significant 32-bit value of the sequence number is used to contain a
boot count, and the remainder 32-bit value is used as an ordinary
32-bit monotonically increasing sequence number. In Generic
Cryptographic Authentication, the remainder 32-bit value is required
to increase occasionally, while in Generic Meticulous Cryptographic
Authentication, the lower order 32-bit sequence number MUST be
incremented for every BFD packet sent by a BFD device. The BFD
Bhatia , et al. Expires October 19, 2014 [Page 9]
Internet-Draft BFD Generic Authentication April 2014
implementations are required to retain the boot count in non-volatile
storage for the deployment life the BFD device. The boot count
increases each time when the BFD device loses its prior sequence
number state. The SNMPv3 snmpEngineBoots variable [RFC4222] MAY be
used for this purpose. However, maintaining a separate boot count
solely for BFD sequence numbers has the advantage of decoupling SNMP
re-initialization and BFD re-initialization. Also, in the rare event
that the lower order 32- bit sequence number wraps, the boot count
can be incremented to preserve the strictly increasing property of
the aggregate sequence number. Hence, a separate BFD boot count is
RECOMMENDED.
4. IANA Considerations
IANA is requested to assign two authentication types from the "BFD
Authentication Types" sub-registry within the "Bidirectional
Forwarding Detection (BFD) Parameters" registry.
+---------+-----------------------------------------+---------------+
| Address | BFD Authentication Type Name | Reference |
+---------+-----------------------------------------+---------------+
| TBD1 | Cryptographic Authentication | This document |
| TBD2 | Meticulous Cryptographic Authentication | This document |
+---------+-----------------------------------------+---------------+
5. Security Considerations
The proposed sequence number extension offers most of the benefits of
more complicated mechanisms involving challenges. There are,
however, a couple drawbacks to this approach.
First, it requires the BFD implementation to be able to save its boot
count in non-volatile storage. If the non-volatile storage is ever
repaired or upgraded such that the contents are lost or the BFD
device is replaced with a model, the keys MUST be changed to prevent
replay attacks.
Second, if a device is taken out of service completely (either
intentionally or due to a persistent failure), the potential exists
for re-establishment of a BFD adjacency by replaying the entire BFD
session establishment. This scenario is however, extremely unlikely
and can be easily avoided. For instance, after recovering from a
system failure, a BFD device has to re-establish BFD sessions. At
this stage, if the device randomly selects its discriminators to
identify new BFD sessions, the possibility of re-establishing a BFD
session by replaying the entire BFD session establishment will be
eliminated. For the implementations in which discriminators are not
randomly selected, this issue can be largely mitigated by integrating
Bhatia , et al. Expires October 19, 2014 [Page 10]
Internet-Draft BFD Generic Authentication April 2014
the boot count of the remote BFD router in the generation of the
authentication data for outgoing BFD packets. Of course, this attack
could also be thwarted by changing the relevant manual keys.
There is a transition mode suggested where devices can ignore the
CRYPTO_AUTH or the MET_CRYPTO_AUTH information carried in the
packets. The operator must ensure that this mode is only used when
migrating to the new CRYPTO_AUTH/MET_CRYPTO_AUTH based authentication
scheme as this leaves the device vulnerable to an attack.
6. Acknowledgements
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010.
7.2. Informative References
[Dobb96a] Dobbertin, H., "Cryptanalysis of MD5 Compress", May 1996.
[Dobb96b] Dobbertin, H., "The Status of MD5 After a Recent Attack",
CryptoBytes", 1996.
[I-D.ietf-karp-crypto-key-table]
Housley, R., Polk, T., Hartman, S., and D. Zhang,
"Database of Long-Lived Symmetric Cryptographic Keys",
draft-ietf-karp-crypto-key-table-10 (work in progress),
December 2013.
[MD5-attack]
Wang, X., Feng, D., Lai, X., and H. Yu, "Collisions for
Hash Functions MD4, MD5, HAVAL-128 and RIPEMD", August
2004.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
[RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005.
Bhatia , et al. Expires October 19, 2014 [Page 11]
Internet-Draft BFD Generic Authentication April 2014
[RFC4222] Choudhury, G., "Prioritized Treatment of Specific OSPF
Version 2 Packets and Congestion Avoidance", BCP 112, RFC
4222, October 2005.
[RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for
Routing Protocols (KARP) Design Guidelines", RFC 6518,
February 2012.
[SHA-1-attack1]
Wang, X., Yin, Y., and H. Yu, "Finding Collisions in the
Full SHA-1", 2005.
[SHA-1-attack2]
Wang, X., Yao, A., and F. Yao, "New Collision Search for
SHA-1", 2005.
Authors' Addresses
Manav Bhatia
Alcatel-Lucent
Bangalore
India
Email: manav.bhatia@alcatel-lucent.com
Vishwas Manral
Hewlett-Packard Co.
19111 Pruneridge Ave.
Cupertino, CA 95014
USA
Email: vishwas.manral@hp.com
Dacheng Zhang
Huawei
Beijing
China
Email: zhangdacheng@huawei.com
Bhatia , et al. Expires October 19, 2014 [Page 12]
Internet-Draft BFD Generic Authentication April 2014
Mahesh Jethanandani
Ciena Corporation
3939 North 1st Street
San Jose, CA 95110
USA
Phone: +1 (408) 904-2160
Fax: +1 (408) 944-9290
Email: mjethanandani@gmail.com
Bhatia , et al. Expires October 19, 2014 [Page 13]
