Internet DRAFT - draft-decimo-babel-dtls
draft-decimo-babel-dtls
Network Working Group A. Decimo
Internet-Draft IRIF, University of Paris-Diderot
Updates: 6126bis (if approved) D. Schinazi
Intended status: Standards Track Apple Inc.
Expires: January 3, 2019 J. Chroboczek
IRIF, University of Paris-Diderot
July 2, 2018
Babel Routing Protocol over Datagram Transport Layer Security
draft-decimo-babel-dtls-01
Abstract
This documents describes how to use Datagram Transport Layer Security
(DTLS) to secure the Babel Routing Protocol.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 3, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components 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.
Decimo, et al. Expires January 3, 2019 [Page 1]
Internet-Draft Babel over DTLS July 2018
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Specification of Requirements . . . . . . . . . . . . . . 3
2. Operation of the Protocol . . . . . . . . . . . . . . . . . . 3
3. Handling protected and unprotected data . . . . . . . . . . . 3
3.1. Cleartext and DTLS on the same port . . . . . . . . . . . 3
3.2. Cleartext and DTLS on separate ports . . . . . . . . . . 4
4. Establishing and handling Babel over DTLS sessions . . . . . 4
4.1. Session Initiation . . . . . . . . . . . . . . . . . . . 4
4.2. Transmission . . . . . . . . . . . . . . . . . . . . . . 4
4.3. Reception . . . . . . . . . . . . . . . . . . . . . . . . 5
4.4. Neighbour flush . . . . . . . . . . . . . . . . . . . . . 5
5. Interface MTU Issues . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Performance Considerations . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Babel over DTLS is a security protocol for the Babel routing protocol
[RFC6126bis], that uses Datagram Transport Layer Security (DTLS)
[RFC6347]. This document describes how to protect Babel with Babel
over DTLS.
The motivation for proposing Babel over DTLS is that DTLS provides a
sub-layer of security that is well-defined, whose security has been
shown, and that has multiple implementations. Babel over DTLS has
the following properties, inherited from DTLS:
o authentication of peers;
o integrity of data;
o confidentiality of data;
o use of asymmetric keys.
The main change to the Babel protocol is that Babel over DTLS
requires most packets to be sent over unicast.
A malicious entity in range of a non-secured deployment of Babel can
learn properties of the network, but also reroute legitimate traffic
by advertising routes with a low metric.
Decimo, et al. Expires January 3, 2019 [Page 2]
Internet-Draft Babel over DTLS July 2018
1.1. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Operation of the Protocol
At first sight, there are incompatibilities between Babel and DTLS.
Babel is a pure peer-to-peer protocol, while DTLS is a two parties
client-server protocol. A Babel implementation typically uses
unicast and multicast, while DTLS can only protect unicast.
The problem of assigning a client of server role for a DTLS handshake
to Babel nodes is solved by a simple arbitrary choice. The addresses
of the two nodes are compared, and the node with the lowest address
acts as the server.
Babel is sufficiently flexible to work almost without multicast. In
Babel over DTLS, almost all packets are sent via unicast. Packets
that would have been sent via unicast needs to be duplicated and sent
to all of the original recipients via unicast. The cost of
duplication is balanced by the fact that on networks with low
throughput, unicast is often far more effective than multicast. Only
neighbour discovery packets are sent via multicast, as they do not
represent a security threat.
3. Handling protected and unprotected data
A Babel node needs to receive unprotected data for bootstrapping
reasons, as well as protected data. Protected and unprotected
traffic needs to be differentiated.
[ NOTE TO READER: AUTHORS ARE CONSIDERING THESE TWO OPTIONS BUT ONLY
ONE WILL BE RETAINED IN THE FINAL DOCUMENT. ]
3.1. Cleartext and DTLS on the same port
In this approach, Babel and Babel over DTLS traffic is received on
the same port. The DTLS client port, the DTLS server port, and the
Babel port (6696) are equal. When a packet is received, it is
unconditionally treated as a DTLS packet and decrypted.
o If the decryption is successful, the decrypted content is parsed
as a Babel packet and the node acts on it.
Decimo, et al. Expires January 3, 2019 [Page 3]
Internet-Draft Babel over DTLS July 2018
o Otherwise, the packet is parsed as a Babel packet and the node
MUST silently ignore all TLVs except Hello and IHU.
Since the source port is fixed as 6696, a node that loses its DTLS
state (e.g. if it reboots), will reuse the same source and
destination ports for the new session. In order to avoid discarding
these new packets, nodes receiving an unexpected DTLS ClientHello
MUST proceed with a new handshake and MUST NOT destroy the existing
session until the new session's handshake completes to avoid denial
of service attacks (Section 4.2.8 of [RFC6347]).
3.2. Cleartext and DTLS on separate ports
In this approach, a different port (number TBD) is allocated by IANA
for Babel over DTLS traffic. The Babel over DTLS server listens on
this port and Babel over DTLS clients use an ephemeral source port to
initiate outbound DTLS connections. Unprotected Babel messages are
sent and received over the standard Babel port (6696). When parsing
unprotected packets, all Babel TLVs except Hello and IHU MUST be
silently ignored.
4. Establishing and handling Babel over DTLS sessions
4.1. Session Initiation
When a node A acquires a new neighbour B (e.g. when A first receives
a Babel packet from B, see Section 3.4 of [RFC6126bis]),
o if the IP address A uses to send and receive Babel packets is
smaller than the source IP address of the received Babel packet
from B, A initialises its DTLS state as a server for peer B;
o otherwise, A initialises its DTLS state as a client for peer B,
and initiates a DTLS handshake.
Once the handshake succeeds and a DTLS session is established, nodes
send all unicast Babel messages over DTLS.
4.2. Transmission
Since DTLS cannot secure multicast, nodes SHOULD send all TLVs over
unicast DTLS, if possible. All TLVs that are not Hello nor IHU MUST
be sent over unicast DTLS. Hello and IHU TLVs MAY be sent either
over unicast DTLS or unprotected multicast. Nodes MUST NOT send any
unprotected packets over unicast.
Decimo, et al. Expires January 3, 2019 [Page 4]
Internet-Draft Babel over DTLS July 2018
4.3. Reception
Packets received over unicast DTLS are parsed the same way as any
packets in the original specification of Babel. Nodes MUST parse
unprotected packets received over multicast, however they MUST
silently ignore any TLV that is not Hello or IHU. Unprotected
packets received over unicast MUST be silently ignored.
4.4. Neighbour flush
When a neighbour entry is flushed from the neighbour table
(Appendix A of [RFC6126bis]), its associated DTLS state SHOULD be
discarded. The node MAY send a DTLS close_notify alert to the
neighbour.
5. Interface MTU Issues
Compared to normal Babel, DTLS adds at least 13 octets of header,
plus cipher and authentication overhead to every packet. This
reduces the size of the Babel payload that can be carried.
As stated in Section 4 of [RFC6126bis], in order to minimise the
number of packets being sent while avoiding lower-layer
fragmentation, a Babel node SHOULD attempt to maximise the size of
the packets it sends, up to the outgoing interface's MTU adjusted for
lower-layer headers (28 octets for UDP over IPv4, 48 octets for UDP
over IPv6). It MUST NOT send packets larger than the attached
interface's MTU adjusted for lower-layer headers or 512 octets,
whichever is larger, but not exceeding 2^16 - 1 adjusted for lower-
layer headers. Every Babel speaker MUST be able to receive packets
that are as large as any attached interface's MTU adjusted for lower-
layer headers or 512 octets, whichever is larger. Babel packets MUST
NOT be sent in IPv6 Jumbograms.
Theses requirements are retained by this specification, but are
extended to take DTLS overhead into account as follows. The Babel
node MUST ensure that the DTLS datagram size does not exceed the
interface MTU, i.e., each DTLS record MUST fit within a single
datagram, as required by [RFC6347]. A Babel node MUST consider the
amount of record expansion expected by the DTLS processing when
calculating the maximum size of Babel packet that fits within the
interface MTU. The overhead can be computed as DTLS overhead of 13
octets + authentication overhead of the negotiated DTLS cipher suite
+ block padding (Section 4.1.1.1 of [RFC6347]).
Decimo, et al. Expires January 3, 2019 [Page 5]
Internet-Draft Babel over DTLS July 2018
6. IANA Considerations
If the final version of this specification uses the standard Babel
port for unprotected packets and DTLS Section 3.1, no actions are
required from IANA.
If the final version of this specification uses separate ports for
unprotected packets and DTLS Section 3.2, IANA is requested to assign
a UDP port with label "Babel_DTLS".
7. Security Considerations
The interaction between two Babel peers requires Datagram Transport
Layer Security (DTLS) with a cipher suite offering confidentiality
protection. The guidance given in [RFC7525] MUST be followed to
avoid attacks on DTLS. The DTLS client SHOULD use the TLS
Certificate Status Request extension (Section 8 of [RFC6066]).
A malicious client might attempt to perform a high number of DTLS
handshakes with a server. As the clients are not uniquely identified
by the protocol and can be obfuscated with IPv4 address sharing and
with IPv6 temporary addresses, a server needs to mitigate the impact
of such an attack. Such mitigation might involve rate limiting
handshakes from a given subnet or more advanced DoS/DDoS avoidance
techniques beyond the scope of this document.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6126bis]
Chroboczek, J. and D. Schinazi, "The Babel Routing
Protocol", Internet Draft draft-ietf-babel-rfc6126bis-05,
October 2017.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Decimo, et al. Expires January 3, 2019 [Page 6]
Internet-Draft Babel over DTLS July 2018
8.2. Informative References
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <https://www.rfc-editor.org/info/rfc7250>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[RFC7918] Langley, A., Modadugu, N., and B. Moeller, "Transport
Layer Security (TLS) False Start", RFC 7918,
DOI 10.17487/RFC7918, August 2016,
<https://www.rfc-editor.org/info/rfc7918>.
[RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security
(TLS) Cached Information Extension", RFC 7924,
DOI 10.17487/RFC7924, July 2016,
<https://www.rfc-editor.org/info/rfc7924>.
[RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
Transport Layer Security (DTLS)", RFC 8094,
DOI 10.17487/RFC8094, February 2017,
<https://www.rfc-editor.org/info/rfc8094>.
Appendix A. Performance Considerations
To reduce the number of octets taken by the DTLS handshake,
especially the size of the certificate in the ServerHello (which can
be several kilobytes), Babel peers can use raw public keys [RFC7250]
or the Cached Information Extension [RFC7924]. The Cached
Information Extension avoids transmitting the server's certificate
and certificate chain if the client has cached that information from
a previous TLS handshake. TLS False Start [RFC7918] can reduce round
trips by allowing the TLS second flight of messages
(ChangeCipherSpec) to also contain the (encrypted) Babel packet.
These performance considerations were inspired from the ones for DNS
over DTLS [RFC8094].
Decimo, et al. Expires January 3, 2019 [Page 7]
Internet-Draft Babel over DTLS July 2018
Authors' Addresses
Antonin Decimo
IRIF, University of Paris-Diderot
Paris
France
Email: antonin.decimo@gmail.com
David Schinazi
Apple Inc.
One Apple Park Way
Cupertino, California 95014
USA
Email: dschinazi@apple.com
Juliusz Chroboczek
IRIF, University of Paris-Diderot
Case 7014
75205 Paris Cedex 13
France
Email: jch@irif.fr
Decimo, et al. Expires January 3, 2019 [Page 8]
