One document matched: draft-ietf-ipngwg-esp-00.txt
Network Working Group Randall Atkinson
Internet Draft Naval Research Laboratory
draft-ietf-ipngwg-esp-00.txt 16 February 1995
IPv6 Encapsulating Security Payload (ESP)
STATUS OF THIS MEMO
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas, and
its working groups. Note that other groups may also distribute working
documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of 6 months.
Internet Drafts may be updated, replaced, or obsoleted by other
documents at any time. It is not appropriate to use Internet Drafts as
reference material or to cite them other than as "work in progress".
This particular Internet Draft is a product of the IETF's IPng
working group. It is intended that a future version of this draft be
submitted to the IPng Area Directors and the IESG for possible
publication as a standards-track protocol. Discussion of this draft
takes place on the IPng Working Group mailing list:
ipng@sunroof.eng.sun.com
1. INTRODUCTION
This memo describes the IPv6 Encapsulating Security Payload (ESP).
ESP seeks to provide integrity and confidentiality to IPv6 datagrams.
It may also provide authentication, depending on which algorithm and
algorithm mode are used. Non-repudiation and protection from traffic
analysis are not provided by ESP. The IPv6 Authentication Header (AH)
might provide non-repudiation if used with certain authentication
algorithms. The IPv6 Authentication Header may be used in conjunction
with ESP to provide authentication. Users desiring integrity and
authentication without confidentiality should use the IPv6
Authentication Header (AH) instead of ESP. This document assumes that
the reader is familiar with the related document "IPv6 Security
Architecture", which defines the overall security architecture for
IPv6 and provides important background for this specification.
Atkinson [Page 1]
Internet Draft IPv6 Encapsulating Security 16 February 1995
1.1 OVERVIEW
The IPv6 Encapsulating Security Payload (ESP) seeks to provide
confidentiality and integrity by encrypting data to be protected and
placing the encrypted data in the data portion of the IPv6
Encapsulating Security Payload. Either a transport-layer (e.g. UDP or
TCP) frame may be encrypted or an entire IPv6 datagram may be
encrypted, depending on the user's security requirements.
Encapsulating the protected data is necessary to provide
confidentiality for the entire original datagram, but can be very
expensive to implement. Use of this specification will increase the
IPv6 protocol processing costs in participating systems and will
also increase the communications latency. The increased latency is
primarily due to the encryption and decryption required for each IPv6
datagram containing an Encapsulating Security Payload.
In order for ESP to work properly without changing the entire
Internet infrastructure (e.g. non-participating systems), the original
IPv6 datagram is placed in the encrypted portion of the Encapsulating
Security Payload and that entire ESP frame is placed within an
datagram having unencrypted IPv6 headers. The information in the
unencrypted IPv6 headers is used to route the secure datagram from
origin to destination. An unencrypted IPv6 Routing Header might be
included between the IPv6 Header and the Encapsulating Security
Payload. An IPv6 Authentication Header may be present both as an
header of the unencrypted IPv6 packet and also as a header within the
encrypted IPv6 packet. In such a case, the unencrypted Authentication
Header is primarily used to provide protection for the contents of the
unencrypted IPv6 headers and the encrypted Authentication Header is
used to provide authentication for the encrypted IPv6 packet.
The encapsulating security payload is structured a bit differently
than other IPv6 payloads. The first component of the ESP payload
consist of the unencrypted field(s) of the payload. The second
component consists of encrypted data. The field(s) of the unencrypted
ESP header inform the intended receiver how to properly decrypt and
process the encrypted data. The encrypted data component includes
protected fields for the security protocol and also the encrypted
encapsulated IPv6 datagram.
2. KEY MANAGEMENT
Key management is an important part of the IPv6 security
architecture. However, a specific key management protocol is not
included in this specification because of a long history in the public
literature of subtle flaws in key management algorithms and protocols.
IPv6 tries to decouple the key management mechanisms from the security
protocol mechanisms. The only coupling between the key management
Atkinson [Page 2]
Internet Draft IPv6 Encapsulating Security 16 February 1995
protocol and the security protocol is with the Security Association
Identifier (SAID), which is described in more detail below. This
decoupling permits several different key management mechanisms to be
used. More importantly, it permits the key management protocol to be
changed or corrected without unduly impacting the security protocol
implementations. Thus, a key management protocol for IPv6 is not
specifed within this draft. The IPv6 Security Architecture describes
key management in more detail and specifies the key management
requirements for IPv6. Those key management requirements are
incorporated here by reference. [Atk95a]
The key management mechanism is used to negotiate a number of
parameters for each security association, including not only the keys
but other information (e.g. the cryptographic algorithms and modes,
security classification level if any) used by the communicating
parties. The key management protocol implementation usually creates
and maintains a logical table containing the several parameters for
each current security association. An ESP implementation normally
needs to read that security parameter table to determine how to
process each datagram containing an ESP (e.g. which algorithm/mode and
key to use).
3. ENCAPSULATING SECURITY PAYLOAD SYNTAX
The Encapsulating Security Payload (ESP) may appear anywhere after
the IPv6 header. The Internet Assigned Numbers Authority has assigned
Protocol Number 50 to IPv6 ESP. Thus the header immediately preceding
the ESP header will always contain the value 50 in its Next Header
field. ESP consists of an unencrypted header followed by encrypted
data. The encrypted data includes both the protected ESP header
fields and the protected user data, which is either an entire IPv6
datagram or an upper-layer protocol frame (e.g. TCP or UDP). A
high-level diagram of a secure IPv6 datagram follows.
|<-- Unencrypted -->|<---- Encrypted ------>|
+-------------+--------------------+------------+---------------------+
| IPv6 Header | Other IPv6 Headers | ESP Header | encrypted data |
+-------------+--------------------+------------+---------------------+
A more detailed diagram of the ESP Header follows. In this diagram, the
cleartext fields are detailed.
+-------------+--------------------+------------+---------------------+
| Security Association Identifier (SAID), 32 bits |
+-------------+--------------------+------------+---------------------+
| Syncronisation Data, variable length |
+=============+====================+============+=====================+
| Encrypted Data, variable length |
Atkinson [Page 3]
Internet Draft IPv6 Encapsulating Security 16 February 1995
+-------------+--------------------+------------+---------------------+
After decryption, the data transmitted in the above "Encrypted Data" field
is formatted as follows:
+-------------+--------------------+-----------------+----------------+
| Next Header | Header Length | Reserved |
+-------------+--------------------+-----------------+----------------+
| Protected data (either an entire IPv6 datagram |
| or a UDP frame or a TCP frame), variable length |
+-------------+--------------------+-----------------+----------------+
3.1 CLEARTEXT FIELDS
The IPv6 Header is the conventional IPv6 Header defined by others in
a separate Internet Draft. The ESP unencrypted field(s) are as follows:
_S_E_C_U_R_I_T_Y _A_S_S_O_C_I_A_T_I_O_N _I_D_E_N_T_I_F_I_E_R (_S_A_I_D)
A 32-bit pseudo-random value identifying the security association
for this datagram. If no security association has been established,
the value of this field shall be 0x00000000. The set of SAID values
in the range 0x00000001 though 0x000000FF are reserved for future use.
A security association is normally one-way. An authenticated
communications session between two hosts will normally have two SAIDs
in use (one in each direction).
This receiver-orientation implies that, in the case of unicast
traffic, the destination system will normally select the SAID value.
By having the destination select the SAID value, there is no potential
for manually configured Security Associations that conflict with
automatically configured (e.g. via a key management protocol) Security
Associations. For multicast traffic, there are multiple destination
systems but a single destination multicast group, so some system or
person will need to select SAIDs for that multicast group and then
communicate the information to all of the legitimate members of that
multicast group via mechanisms not defined here.
Senders to a multicast group may share a common SAID for all
communications if all communications are authenticated using the same
security configuration parameters (e.g. algorithm, key, security
classification level, etc.). In this case, the receiver only knows
that the message came from a host knowing the security association
data for the group and cannot authenticate which member of the group
sent the datagram. Multicast groups may also use a separate SAID for
each sender. In any event, the combination of Destination Address and
SAID is used to determine the correct security association data. If
each sender is keyed separately and asymmetric algorithms are used,
data origin authentication is also a provided service.
Atkinson [Page 4]
Internet Draft IPv6 Encapsulating Security 16 February 1995
Each SAID value implies the key(s) used to encrypt and decrypt the
encrypted portion of the ESP payload, the sensitivity level (e.g.
Secret, Unclassified) of the user data in the ESP payload, the
encryption algorithm being used, the block size (if any) of the
encryption algorithm, the authentication algorithm being used (if
separate from the encryption algorithm), the block size (if any) of
the authentication algorithm, and the presence/absence and size of a
cryptographic synchronisation or initialisation vector field at the
start of the encrypted portion of the ESP (if no such field is
present, then the size is of course zero).
The sending host uses the sending userid and destination host to
select an appropriate Security Association (and hence SAID value).
The receiving host uses the combination of SAID value and originating
address to distinguish the correct association. Hence, an ESP
implementation will always be able to use the SAID in combination with
the 128-bit Destination Address to determine the security association
and related security configuration data for all valid incoming
packets.
_S_Y_N_C_H_R_O_N_I_S_A_T_I_O_N _D_A_T_A
This field is present only for algorithms which require a
cryptographic synchronisation field for each packet. The value of
this field is arbitrary. The length of this field is variable, though
for any given algorithm it has a particular known length. It is
considered to be plaintext in this document, though most users will
not be able to make sense of its contents. Its presence or absence
and its size are constant for all secure datagrams of any given SAID
value. The ESP specification includes this field so that the payload
specification will be independent of the cryptographic algorithm that
is being used by the communicating systems. If present, the field
contains cryptographic synchronisation data, such as a DES
Initialisation Vector, for whichever algorithm is in use. [ISO92b]
An ESP implementation will normally use the Security Association
Identifier value for the payload being processed to determine whether
this field is present and to determine the field's size and use if
present.
3.2 ENCRYPTED FIELDS
The ESP encrypted fields are as follows:
_N_E_X_T _H_E_A_D_E_R
This field contains the value indicating which header follows the
ESP Encrypted Fields. For example, if an entire IP datagram follows,
the field will contain the number 94, which has been allocated by IANA
to indicate IPv4 has been encapsulated. [STD-2] If the field contains
the number 41, it means that IPv6 has been encapsulated. [STD-2]
Atkinson [Page 5]
Internet Draft IPv6 Encapsulating Security 16 February 1995
_H_E_A_D_E_R _L_E_N_G_T_H
This field is contains the length of the set of encrypted ESP fields
(i.e. Next Header, Header Length, Reserved) minus the 8 byte minimum
length. The minimum length is 64-bit aligned to comply with normal
IPv6 alignment rules.
_R_E_S_E_R_V_E_D
This field is currently used primarily for padding out to 64-bit
alignment but might be used for other purposes in the future. In
order to permit such future reuse without breaking previously deployed
implementations, this field MUST be set to zero on transmission and
MUST be ignored upon receipt. It is 16 bits long.
It is important that all routing headers and other data be included
within the encrypted IPv6 datagram, even if the same data is in the
unencrypted part of the IPv6 datagram. The receiving system shall
ignore all routing information in the unencrypted portion of the
received datagram and shall strictly rely on the routing information
from the protected payload instead. If this rule is not strictly
adhered to, then the system will be vulnerable to various kinds of
attacks, including source routing attacks. [Bel89][CB94][CERT95]
The encrypted IPv6 datagram need not contain any explicit Security
Label because the SAID indicates the sensitivity label for the
encrypted IPv6 datagram. This is an improvement over the current
practices with IPv4 where an explicit Security Label is normally used
with Compartmented Mode Workstations and other systems requiring
Security Labels. [Ken91] [DIA]
If it is necessary to pad the protected data (e.g. to an integral
block-size of the cryptographic algorithm in use), then the normal
IPv6 Padding header is used to provide that padding. This means that
ESP will not work with block-oriented algorithms whose block size is
not an integral number of 8-bit bytes.
4. ENCAPSULATING SECURITY PROTOCOL PROCESSING
This section describes the steps taken when ESP is in use between
two communicating parties. Multicast is different from unicast only
in the area of key management (See the definition of the SAID, above,
for more detail on this). There are two modes of use for ESP. The
first mode, which is called "IP-mode", encapsulates an entire IP
datagram inside ESP. The second mode, which is called
"Transport-Mode", encapsulates a transport-layer (e.g. UDP or TCP)
frame inside ESP. These terms should not be misconstrued as
restrictive, for example an ICMP/IGMP message might be sent either
using the "Transport-mode" or the "IP-mode" depending upon
circumstance. This section describes protocol processing for each of
these two modes.
Atkinson [Page 6]
Internet Draft IPv6 Encapsulating Security 16 February 1995
4.1 ESP in IP-mode
The sender takes the original IPv6 datagram, encapsulates it into
the ESP and then applies the encryption algorithm using the
appropriate key for combination of sending userid and the receiving
party. If no key has been established, then the key management
mechanism is used to establish a encryption key for this
communications session prior to the encryption. The (now encrypted)
ESP is then encapsulated in a cleartext IPv6 datagram as the last
payload. If strict red/black separation is being enforced, then the
addressing and other information in the cleartext IPv6 headers and
optional payloads might be different from the values contained in the
(now encrypted and encapsulated) original datagram.
The receiver strips off the cleartext IPv6 header and cleartext
optional IPv6 payloads (if any) and discards them. It then uses the
combination of Destination Address and SAID value to locate the
correct decryption key to use for this packet. Then, it decrypts
the ESP using the session key that has been established for this
traffic.
If no cryptographic key exists for this session, the encrypted ESP
MUST be discarded and the failure MUST recorded in the system or audit log.
This audit log entry SHOULD include the cleartext values for the SAID,
date/time, Sending Address, Destination Address, and the Flow ID.
If decryption succeeds, the original IPv6 datagram is then removed
from the (now decrypted) ESP. This original IPv6 datagram is then
processed as per the normal IPv6 protocol specification. In the case
of a B1 or Compartmented Mode Workstation, additional appropriate
mandatory access controls SHOULD be applied based on the security
level of the receiving process and the security level associated with
this Security Association.
4.2 ESP in Transport-mode
The sender takes the original UDP or TCP or ICMP frame, encapsulates
it into the ESP and then applies the encryption algorithm using the
appropriate key for the combination of sending userid and receiving
party. If no key has been established, then the key management
mechanism is used to establish a encryption key for this
communications session prior to the encryption. The (now encrypted)
ESP is then encapsulated as the last payload of a cleartext IPv6
datagram.
The receiver processes the cleartext IPv6 header and cleartext
optional IPv6 headers (if any) and temporarily stores pertinent
information (e.g. source and destination addresses, Flow ID, Routing
Atkinson [Page 7]
Internet Draft IPv6 Encapsulating Security 16 February 1995
Header). It then decrypts the ESP using the session key that has been
established for this traffic, using the combination of the destination
address and the packet's Security Association Identifier (SAID) to
locate the correct key.
If no key exists for this session, the encrypted ESP MUST be discarded
and the failure MUST be recorded in the system or audit log. If such a
failure occurs, the recorded log data SHOULD include the cleartext
values for the SAID, date/time received, Sending Address, Destination
Address, and the Flow ID. The log data may also include other
information about the failed packet.
If decryption succeeds, the original UDP or TCP frame is removed
from the (now decrypted) ESP. The information from the cleartext IPv6
header and the now decrypted UDP or TCP header is jointly used to
determine which application the data should be sent to. The data is
then sent along to the appropriate application as normally per IPv6
protocol specification. In the case of a B1 or Compartmented Mode
Workstation, additional Mandatory Access Controls SHOULD be applied
based on the security level of the receiving process and the security
level of the received packet's Security Association.
4.3. Combining ESP and the Authentication Header
This section describes how to combine the Encapsulating Security
Protocol with Authentication Header. There are two different
approaches, depending on which data is to be authenticated. The
location of the IPv6 Authentication Header makes it clear which set of
data is being authenticated.
In the first usage, the entire received datagram is authenticated,
including both the encrypted and unencrypted portions, while only the
data sent after the ESP Header is confidential. In this usage, the
sender first applies ESP to the data being protected. Then the other
plaintext IPv6 headers are prepended to the ESP header and its now
encrypted data. Finally, the IPv6 Authentication Header is calculated
over the resulting datagram according to the normal method. Upon
receipt, the receiver first verifies the authenticity of the entire
datagram using the normal IPv6 Authentication Header process. Then if
authentication succeeds, decryption using the normal IPv6 ESP process
occurs. If decryption is successful, then the resulting data is
passed up to the upper layer.
If the authentication process were to be applied only to the data
protected by IPv6 ESP and the protected data were an entire IPv6
datagram, then the IPv6 Authentication Header would be placed normally
within that protected datagram. However, if the protected data were
less than an entire IPv6 datagram, then the IPv6 Authentication Header
Atkinson [Page 8]
Internet Draft IPv6 Encapsulating Security 16 February 1995
would be placed within the encrypted payload immediately after the ESP
protected header and before any other header or the UDP or TCP frame.
If the Authentication Header is encapsulated within the ESP header,
and both headers have specific security classification levels
associated with them, and the two security classification levels are
not identical, then an error has occurred. That error SHOULD be
recorded in the system or audit log using the procedures described
previously. It is not necessarily an error for an Authentication
Header located outside of the ESP header to have a different security
classification level than the ESP header's classification level. This
is true because the cleartext IP headers might have a different
classification level when the data is encrypted using ESP.
6. TYPICAL USE
The ESP supports security between two or more hosts implementing
ESP, between two or more gateways implementing ESP, and between a host
or gateway implementing ESP and a set of hosts and/or gateways. A
security gateway is a system which acts as the communications gateway
between external untrusted systems and trusted hosts on their own
subnetwork and provides security services for the trusted hosts when
they communicate with external untrusted systems. A trusted
subnetwork contains hosts and routers that trust each other not to
engage in active or passive attacks and trust that the underlying
communications channel (e.g. an Ethernet) isn't being attacked.
Trusted systems always should be trustworthy, but in practice they
often are not trustworthy.
In the case where a security gateway is providing services on behalf
of one or more hosts on a trusted subnet, the security gateway is
responsible for establishing the security association on behalf of its
trusted host and for providing security services between the security
gateway and the external system(s). In this case, only the gateway
need implement ESP, while all of the systems behind the gateway on the
trusted subnet may take advantage of ESP services between the gateway
and external systems. A gateway which receives a datagram containing
a recognised sensitivity label from a trusted host should take that
label's value into consideration when creating/selecting an SAID for
use with ESP between the gateway and the external destination. In
such an environment, a gateway which receives a IPv6 packet containing
the ESP should appropriately label the decrypted packet that it
forwards to the trusted host that is the ultimate destination. The
IPv6 Authentication Header should always be used on packets containing
explicit sensitivity labels to ensure end-to-end label integrity.
If there are no security gateways present in the connection, then
two end systems that implement ESP may also use it to encrypt only the
Atkinson [Page 9]
Internet Draft IPv6 Encapsulating Security 16 February 1995
user data (e.g. TCP or UDP) being carried between the two systems.
ESP is designed to provide maximum flexibility so that users may
select and use only the security that they desire and need.
7. SECURITY CONSIDERATIONS
This entire draft discusses a security mechanism for use with IPv6.
This mechanism is not a panacea, but it does provide an important
component useful in creating a secure internetwork.
Users need to understand that the quality of the security provided
by this specification depends completely on the strength of whichever
encryption algorithm that has been implemented, the correctness of
that algorithm's implementation, upon the security of the key
management mechanism and its implementation, the strength of the key
[CN94] and upon the correctness of the ESP and IPv6 implementations in
all of the participating systems. If any of these assumptions do not
hold, then little or no real security will be provided to the user.
Use of high assurance development techniques is recommended for the
IPv6 Encapsulating Security Payload.
Users seeking protection from traffic analysis might consider the use
of appropriate link encryption. Description and specification of link
encryption is outside the scope of this note.
If user-to-user keying is not in use, then the algorithm in use
should not be vulnerable to any kind of Chosen Plaintext attack.
A Chosen Plaintext attack on DES is described in [BS93]. Use of
user-to-user keying is recommended in order to preclude any sort of
Chosen Plaintext attack and to generally make cryptanalysis more
difficult. Implementations MUST support user-to-user keying as
is described in the IPv6 Security Architecture. [Atk95a]
ACKNOWLEDGEMENTS
Many of the concepts here are derived from or were influenced by the
US Government's SP3 security protocol specification, the ISO/IEC's
NLSP specification, or from the proposed swIPe security
protocol. [SDNS89, ISO92a, IB93, IBK93, ISO92b] The use of DES for
confidentiality is closely modeled on the work done for the
SNMPv2. [GM93] Steve Bellovin, Steve Deering, and Dave Mihelcic
provided useful critiques of early versions of this draft.
REFERENCES
[Atk95a] Randall J. Atkinson, IPv6 Security Architecture, Internet Draft,
draft-atkinson-ipng-sec-01.txt, 16 February 1995.
[Atk95b] Randall J. Atkinson, IPv6 Authentication Header, Internet Draft,
draft-atkinson-ipng-auth-01.txt, 16 February 1995.
Atkinson [Page 10]
Internet Draft IPv6 Encapsulating Security 16 February 1995
[Bel89] Steven M. Bellovin, "Security Problems in the TCP/IP Protocol
Suite", ACM Computer Communications Review, Vol. 19, No. 2,
March 1989.
[BS93] Eli Biham and Adi Shamir, "Differential Cryptanalysis of the
Data Encryption Standard", Springer-Verlag, New York, NY, 1993.
[CN94] John M. Carroll & Sri Nudiati, "On Weak Keys and Weak Data:
Foiling the Two Nemeses", Cryptologia, Vol. 18, No. 23,
July 1994. pp. 253-280
[CERT95] Computer Emergency Response Team (CERT), "IP Spoofing Attacks
and Hijacked Terminal Connections", CA-95:01, January 1995.
Available via anonymous ftp from info.cert.org.
[DIA] US Defense Intelligence Agency (DIA), "Compartmented Mode
Workstation Specification", Technical Report DDS-2600-6243-87.
[GM93] James Galvin & Keith McCloghrie, Security Protocols for Version 2
of the Simple Network Management Protocol (SNMPv2), RFC-1446,
DDN Network Information Center, April 1993.
[Hin94] Robert Hinden (Editor), IPv6 Specification, Internet Draft,
draft-hinden-ipng-ipv6-spec-00.txt, October 1994.
[IB93] John Ioannidis & Matt Blaze, "Architecture and Implementation
of Network-layer Security Under Unix", Proceedings of the USENIX
Security Symposium, Santa Clara, CA, October 1993.
[IBK93] John Ioannidis, Matt Blaze, & Phil Karn, "swIPe: Network-Layer
Security for IP", presentation at the Spring 1993 IETF Meeting,
Columbus, Ohio.
[ISO92a] ISO/IEC JTC1/SC6, Network Layer Security Protocol, ISO-IEC
DIS 11577, International Standards Organisation, Geneva,
Switzerland, 29 November 1992.
[ISO92b] ISO/IEC JTC1/SC6, Network Layer Security Protocol, ISO-IEC
DIS 11577, Section 13.4.1, page 33, International Standards
Organisation, Geneva, Switzerland, 29 November 1992.
[Ken91] Steve Kent, "US DoD Security Options for the Internet Protocol
(IPSO)", RFC-1108, DDN Network Information Center, November 1991.
[NIST77] US National Bureau of Standards, "Data Encryption Standard",
Federal Information Processing Standard (FIPS) Publication 46,
January 1977.
Atkinson [Page 11]
Internet Draft IPv6 Encapsulating Security 16 February 1995
[NIST80] US National Bureau of Standards, "DES Modes of Operation"
Federal Information Processing Standard (FIPS) Publication 81,
December 1980.
[NIST81] US National Bureau of Standards, "Guidelines for Implementing and
Using the Data Encryption Standard", Federal Information
Processing Standard (FIPS) Publication 74, April 1981.
[NIST88] US National Bureau of Standards, "Data Encryption Standard",
Federal Information Processing Standard (FIPS) Publication 46-1,
January 1988.
[STD-2] J. Reynolds and J. Postel, "Assigned Numbers", STD-2,
DDN Network Information Center, 20 October 1994.
[Sch94] Bruce Schneier, Applied Cryptography, John Wiley & Sons,
New York, NY, 1994. ISBN 0-471-59756-2
[SDNS89] SDNS Secure Data Network System, Security Protocol 3, SP3,
Document SDN.301, Revision 1.5, 15 May 1989, as published
in NIST Publication NIST-IR-90-4250, February 1990.
DISCLAIMER
The views and specification here are those of the author and are not
necessarily those of his employer. The Naval Research Laboratory has
not passed judgement on the merits, if any, of this work. The author
and his employer specifically disclaim responsibility for any problems
arising from correct or incorrect implementation or use of this
specification.
AUTHOR INFORATION
Randall Atkinson <atkinson@itd.nrl.navy.mil>
Information Technology Division
Naval Research Laboratory
Washington, DC 20375-5320
USA
Telephone: (DSN) 354-8590
Fax: (DSN) 354-7942
Atkinson [Page 12]
Internet Draft IPv6 Encapsulating Security 16 February 1995
APPENDIX A: Use of CBC-Mode DES with IPv6 ESP
This appendix describes the application of the Cipher Block Chaining
(CBC) mode of the US Data Encryption Standard (DES) algorithm to the
IPv6 Encapsulating Security Payload. This mode of DES requires an
Initialisation Vector that is 8 bytes long and requires that the
encrypted data be a multiple of 8 bytes long. DES is described is
several US Government publications. [NIST77, NIST80, NIST81, NIST88] A
recent book also provides information on DES. [Sch94] That same reference
indicates on page 231 that at least one hardware implementation of DES
CBC can encrypt or decrypt at about 1 Gbps.
Each ESP header shall contain a 64-bit DES Initialisation Vector in
the Cryptographic Synchronisation field when DES-CBC is in use. Each
packet needs to contain its own different DES Initialisation Vector.
Including the Initialisation Vector in each packet also ensures
decryption of each received packet can be performed even though other
packets might have been dropped or packets might have been misordered
in transit. The method for selection of the Initialisation Vector
value is implementation-defined.
The secret DES key shared between the communicating parties is 64
bits long, as per the DES specifications [NIST77, NIST80, NIST81,
NIST88]. The 64-bit DES key consists of a 56-bit quantity used by the
DES algorithm and 8 parity bits arranged such that one parity bit is
the least significant bit of each octet.
The length of the octet sequence to be encrypted by the DES
algorithm must be an integral multiple of 8. When encrypting, any
needed padding shall be included by using a IPv6 hop-by-hop padding
option. When the Transport-mode of ESP is used, such padding must
appear between the encrypted ESP header fields and the start of the
UDP or TCP data. If the length of the octet sequence to be decrypted
is not an integral multiple of 8 octets, then processing shall be
halted, the packet shall be discarded, and the event should be
recorded in the system or audit log using implementation-specific
methods.
Atkinson [Page 13]
| PAFTECH AB 2003-2026 | 2026-04-23 17:31:41 |