Light-Weight Implementation Guidance (lwig) D. Migault, Ed.
Internet-Draft Ericsson
Intended status: Informational T. Guggemos
Expires: September 22, 2016 LMU Munich
D. Palomares
Orange
March 21, 2016
Minimal ESP
draft-mglt-lwig-minimal-esp-02.txt
Abstract
This document describes a minimal version of the IP Encapsulation
Security Payload (ESP) described in RFC 4303 which is part of the
IPsec suite.
ESP is used to provide confidentiality, data origin authentication,
connectionless integrity, an anti-replay service (a form of partial
sequence integrity), and limited traffic flow confidentiality.
This document does not update or modify RFC 4303, but provides a
compact description of how to implement the minimal version of the
protocol. If this document and RFC 4303 conflicts then RFC 4303 is
the authoritative description.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 22, 2016.
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Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Security Parameter Index (SPI) (32 bit) . . . . . . . . . . . 3
4. Sequence Number(SN) (32 bit) . . . . . . . . . . . . . . . . 4
5. Padding . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Next Header (8 bit) . . . . . . . . . . . . . . . . . . . . . 5
7. ICV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8. Cryptographic Suites . . . . . . . . . . . . . . . . . . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
10. Security Considerations . . . . . . . . . . . . . . . . . . . 8
11. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 8
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
12.1. Normative References . . . . . . . . . . . . . . . . . . 8
12.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Document Change Log . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Requirements notation
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 [RFC2119].
2. Introduction
ESP [RFC4303] is part of the IPsec suite protocol [RFC4301] . It is
used to provide confidentiality, data origin authentication,
connectionless integrity, an anti-replay service (a form of partial
sequence integrity) and limited traffic flow confidentiality.
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Figure 1 describes an ESP Packet. Currently ESP is implemented in
the kernel of IPsec aware devices. This document provides a minimal
ESP implementation guideline so that smaller devices like sensors
without kernel and with hardware restrictions can implement ESP and
benefit from IPsec.
For each field of the ESP packet represented in Figure 1 this
document provides recommendations and guidance for minimal
implementations.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----
| Security Parameters Index (SPI) | ^Int.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Cov-
| Sequence Number | |ered
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ----
| Payload Data* (variable) | | ^
~ ~ | |
| | |Conf.
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Cov-
| | Padding (0-255 bytes) | |ered*
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| | Pad Length | Next Header | v v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Integrity Check Value-ICV (variable) |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: ESP Packet Description
3. Security Parameter Index (SPI) (32 bit)
According to the [RFC4303], the SPI is a mandatory 32 bits field and
is not allowed to be removed.
The SPI is used to index the Security Association. The SPI MUST be
unique so that any incoming ESP packet can appropriately be bound to
its association. Uniqueness of the SPI may be provided by random
functions. However, the SPI does not need to be unpredictable. As a
result, if random functions are too costly for some constraint
devices, the SPI can be generated using predictable functions or even
fixed values.
If a constraint device is designed to set a single ESP connection
with a single remote device, it can use a fix value for the SPI.
Since the constraint device uses a single connection, there is no
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risk of SPI collision by using a fix value. More specifically, the
collision does not affect the remote device. In fact, when the SPI
is proposed, it is used by the proposing entity to index inbound
traffic. In the case two different constraint devices are using the
same SPI, the remote device ends up with two outbound traffic
identified by the same SPI. Should SPI collision for outbound
traffic does not affect the remote device as the SPI will not be used
by this device to index the traffic.
Similarly, if a constraint device establishes a single ESP connection
with multiple remote devices, it may use the IPv4 or the interface ID
of IPv6 addresses for example.
Values 0-255 SHOULD NOT be used. Values 1-255 are reserved and 0 is
only allowed to be used internal and it MUST NOT be send on the wire.
[RFC4303] mentions :
- "The SPI is an arbitrary 32-bit value that is used by a receiver
to identify the SA to which an incoming packet is bound. The SPI
field is mandatory. [...]"
- "For a unicast SA, the SPI can be used by itself to specify an
SA, or it may be used in conjunction with the IPsec protocol type
(in this case ESP). Because the SPI value is generated by the
receiver for a unicast SA, whether the value is sufficient to
identify an SA by itself or whether it must be used in conjunction
with the IPsec protocol value is a local matter. This mechanism
for mapping inbound traffic to unicast SAs MUST be supported by
all ESP implementations."
4. Sequence Number(SN) (32 bit)
According to [RFC4303], the sequence number is a mandatory 32 bits
field in the packet.
The SN is set by the sender so the receiver can implement anti-replay
protection. The SN is derived from any strictly increasing function
that guarantees: if packet B is sent after packet A, then SN of
packet B is strictly greater then the SN of packet A.
In IoT, constraint devices are expected to establish communication
with specific devices, like a specific gateway, or nodes similar to
them. As a result, the sender may know whereas the receiver
implements anti-replay protection or not. Even though the sender may
know the receiver does not implement anti replay protection, the
sender MUST implement a always increasing function to generate the
SN.
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Usually, SN is generated by incrementing a counter for each packet
sent. A constraint device may avoid maintaining this context. If
the device has a clock, it may use the time indicated by the clock
has a SN. This guarantees a strictly increasing function, and avoid
storing any additional values or context related to the SN.
[RFC4303] mentions :
- "This unsigned 32-bit field contains a counter value that
increases by one for each packet sent, i.e., a per-SA packet
sequence number. For a unicast SA or a single-sender multicast
SA, the sender MUST increment this field for every transmitted
packet. Sharing an SA among multiple senders is permitted, though
generally not recommended. [...] The field is mandatory and MUST
always be present even if the receiver does not elect to enable
the anti-replay service for a specific SA."
5. Padding
[RFC4303] does not specify any way on how Padding bytes should be
generated. These bytes may for example, be generated randomly or
each byte may be numbered from \x01 to \xpad-length. A simplified
implementation may consider a fix value, and consider all Padding
bytes set to zero.
Note that Padding can also be defined by the encryption algorithm
like AES in CBC mode [RFC3602]. In that case, Padding MUST be
performed as described in [RFC3602]. However, [RFC3602] does not
specify how Padding bytes are generated, and AES in CTR [RFC3686] or
GCM[RFC4106] or CCM [RFC4309] mode do not consider Padding.
6. Next Header (8 bit)
According to [RFC4303], the Next Header is a mandatory 8 bits field
in the packet. In some cases, devices are dedicated to a single
application or a single transport protocol, in which case, the Next
Header has a fix value.
[RFC4303] mentions :
- "The Next Header is a mandatory, 8-bit field that identifies the
type of data contained in the Payload Data field, e.g., an IPv4 or
IPv6 packet, or a next layer header and data. [...] the protocol
value 59 (which means "no next header") MUST be used to designate
a "dummy" packet. A transmitter MUST be capable of generating
dummy packets marked with this value in the next protocol field,
and a receiver MUST be prepared to discard such packets, without
indicating an error."
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7. ICV
The ICV is an optional value with variable length. Unless the
crypto-suite provides authentication without the use of the ICV
field, the ICV field is often use to host the authentication part of
the packet.
As detailed in Section 8 we recommend to use authentication, the ICV
field is expected to be present that is to say with a size different
from zero. This makes it a mandatory field which size is defined by
the security recommendations only.
[RFC4303] mentions :
- "The Integrity Check Value is a variable-length field computed
over the ESP header, Payload, and ESP trailer fields. Implicit
ESP trailer fields (integrity padding and high-order ESN bits, if
applicable) are included in the ICV computation. The ICV field is
optional. It is present only if the integrity service is selected
and is provided by either a separate integrity algorithm or a
combined mode algorithm that uses an ICV. The length of the field
is specified by the integrity algorithm selected and associated
with the SA. The integrity algorithm specification MUST specify
the length of the ICV and the comparison rules and processing
steps for validation."
8. Cryptographic Suites
Light implementations of ESP will probably implement a reduce number
of cipher suites. When choosing the cipher suites it is recommended
to balance the number of cipher suites as well as the cipher itself
with other criteria. This section attempts to provide some generic
guidances for choosing the appropriated cipher suites.
This section lists some of the criteria that may be consider. The
list is not expected to be exhaustive and may also evolve overtime.
As a result, the list is provided as indicative:
- Security : Security is the criteria that should be considered
first when a selection of cipher suites is performed. The
security of cipher suites is expected to evolve over time, and
it is of primary importance to follow up-to-date security
guidances and recommendations. The chosen cipher suites MUST
NOT be known vulnerable or weak. ESP can be used to
authenticate only a communication or the encrypt the
communication. In the later case, encryption should be always
considered in conjunction with authentication. [RFC4303]
allows combined encryption and authentication ciphers, which
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enables the use of modes like GCM [RFC4106] or CCM. Note that
the use of AES-CTR for encryption requires the authentication
with a non zero length ICV.
- Interoperability : Interoperability considers the cipher suites
shared by the greatest number of nodes. Note that it is not
because a cipher suite is widely deployed that is secured. As
a result, security should not be weaken for interoperability.
Life cycle of cipher suites is expected to be long enough so
interoperability can still be provided with secure cipher
suites.
- Power Consumption and Cipher Suite Complexity : Complexity of the
cipher suite or the energy associated to it are especially
considered when devices have limited resources or are using
some batteries, in which case the battery main determine the
life of the device. The choice of a cryptographic function may
consider re-using specific libraries or to take advantage of
hardware acceleration provided by the device. For example if
the device benefits from AES hardware modules and uses AES-CTR,
it may prefer AUTH_AES-XCBC over a SHA2 based function for its
authentication. In addition, some devices may also embed radio
modules with hardware acceleration for AES-CCM, in which case,
this mode may be preferred.
- Power Consumption and Bandwidth Consumption : Similarly to the
cipher suite complexity, reducing the payload sent, may
significantly reduce the energy consumption of the device. As
a result, cipher suites with low overhead may be considered.
To reduce the overall payload size one may for example,
consider the length of the ICV associated to the cipher suite,
the use of implicit IV [I-D.mglt-6lo-aes-implicit-iv], the
block size used by the cipher suite. Note that the size of the
payload must not be performed at the expense of acceptable
security. As a result, reducing the size of the ICV MUST
follow the security recommendations. Regarding the block size,
AES-CBC consumes a lot of bandwidth compared to other proposed
modes. AES in CBC mode has a 128 bit alignment which for small
packets of a few bytes length generates a large overhead in
term of extra padding bytes.
9. IANA Considerations
There are no IANA consideration for this document.
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10. Security Considerations
Security considerations are those of [RFC4303].
11. Acknowledgment
12. References
12.1. 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,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3602] Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC Cipher
Algorithm and Its Use with IPsec", RFC 3602,
DOI 10.17487/RFC3602, September 2003,
<http://www.rfc-editor.org/info/rfc3602>.
[RFC3686] Housley, R., "Using Advanced Encryption Standard (AES)
Counter Mode With IPsec Encapsulating Security Payload
(ESP)", RFC 3686, DOI 10.17487/RFC3686, January 2004,
<http://www.rfc-editor.org/info/rfc3686>.
[RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
(GCM) in IPsec Encapsulating Security Payload (ESP)",
RFC 4106, DOI 10.17487/RFC4106, June 2005,
<http://www.rfc-editor.org/info/rfc4106>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <http://www.rfc-editor.org/info/rfc4301>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<http://www.rfc-editor.org/info/rfc4303>.
[RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM
Mode with IPsec Encapsulating Security Payload (ESP)",
RFC 4309, DOI 10.17487/RFC4309, December 2005,
<http://www.rfc-editor.org/info/rfc4309>.
12.2. Informative References
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[I-D.mglt-6lo-aes-implicit-iv]
Migault, D. and T. Guggemos, "Implicit IV for AES-CBC,
AES-CTR, AES-CCM and AES-GCM", draft-mglt-6lo-aes-
implicit-iv-01 (work in progress), February 2015.
Appendix A. Document Change Log
[RFC Editor: This section is to be removed before publication]
-00: First version published.
-01: Clarified description
-02: Clarified description
Authors' Addresses
Daniel Migault (editor)
Ericsson
8400 boulevard Decarie
Montreal, QC H4P 2N2
Canada
Email: daniel.migault@ericsson.com
Tobias Guggemos
LMU Munich
MNM-Team
Oettingenstr. 67
80538 Munich, Bavaria
Germany
Email: guggemos@mnm-team.org
Daniel Palomares
Orange
6 place d'Alleray
75015 Paris
France
Email: daniel.palomares@orange.com
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