Network Working Group M. St. Johns
Request for Comments: 1038 IETF
January 1988
Draft Revised IP Security Option
Status of this Memo
This RFC is a pre-publication draft of the revised Internet Protocol
Security Option. This draft reflects the version as approved by
the Protocol Standards Steering Group. It is provided for
informational purposes only. The final version of this document will
be available from Navy Publications and should not differ from
this document in any major fashion.
This document will be published as a change to the MIL-STD 1777,
"Internet Protocol". Distribution of this memo is unlimited.
9.3.13.1 Internet Options Defined.
The following internet options are defined:
CLASS NUMBER LENGTH DESCRIPTION
_____ ______ ______ ___________
0 00000 - End of Option list: This option occupies
only 1 octet; it has no length octet.
0 00001 - No Operation: This option occupies only 1
octet; it has no length octet.
0 00010 var. Basic Security: Used to carry security
level and accrediting authority flags.
0 00011 var. Loose Source Routing: Used to route the
datagram based on information supplied by
the source.
0 00101 var. Extended Security: Used to carry additional
security information as required by
registered authorities.
0 01001 var. Strict Source Routing: Used to route the
datagram based on information supplied by
the source.
0 00111 var. Record Route: Used to trace the route a
datagram takes.
0 01000 4 Stream ID: Used to carry the stream
identifier.
2 00100 var. Internet Timestamp: Used to accumulate
timing information in transit.
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The option identifies the U.S. security level to which the datagram
is to be protected, and the accrediting authorities whose protection
rules apply to each datagram.
The option is used by accredited trusted components of an internet
to:
a. Validate the datagram as appropriate for transmission from the
source.
b. Guarantee that the route taken by the datagram (including the
destination) is protected to the level required by all
indicated accrediting authorities.
c. Supply common label information required by computer security
models.
This option must be copied on fragmentation. This option appears
at most once in a datagram.
The length of the option is variable. The minimum length option is
4.
9.3.15.3.2 Classification Protection Level.
This field specifies the U.S. classification level to which the
datagram should be protected. The information in the datagram should
be assumed to be at this level until and unless it is regraded in
accordance with the procedures of all indicated protecting
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RFC 1038 Draft Revised IP Security Option January 1988
authorities. This field specifies one of the four U.S.
classification levels, and is encoded as follows:
This field indicates the National Access Program(s) with accrediting
authority whose rules apply to the protection of the datagram.
a. Field Length: This field is variable in length. The low-
order bit (Bit 7) of each octet is encoded as "zero" if it is the
final octet in the field, or as "one" if there are additional
octets. Currently, only one octet is needed for this field
(because there are less than seven authorities), and the final bit
of the first octet is coded as "zero".
b. Source Flags: The first seven bits (Bits 0 through 6) in each
octet are source flags which are each associated with an authority
as indicated below. The bit corresponding to an authority is
"one" if the datagram is to be protected in accordance with the
rules of that authority.
9.3.15.3.4 Usage Rules.
Use of the option requires that a host be aware of 1) the
classification level, or levels, at which it is permitted to operate,
and 2) the protection authorities responsible for its certification.
The achievement of this is implementation dependent. Rules for use
of the option for different types of hosts are given below.
9.3.15.3.4.1 Unclassified Hosts, including gateways.
a. Output: Unclassified hosts may either use or not use the
option. If it is used, classification level must be unclassified,
bit 0 of the accreditation field (GENSER) must be one, and all
other bits of the accreditation field must be 0. While use of the
option is permitted, it is recommended that unclassified hosts
interested in maximizing interoperability with existing non-
compliant implementations not use the option.
b. Input: Unclassified hosts should accept for further
processing IP datagrams without the option. If the option is
present on an incoming IP datagram, then the datagram is accepted
for further processing only if the classification level is
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unclassified, bit 0 of the accreditation field (GENSER) is one,
and all other bits of the accreditation field are zero.
Otherwise, the out-of-range procedure is followed.
9.3.15.3.4.2 Hosts accredited in the Dedicated, System-High, or
Compartmented Modes at a classification level higher than unclassified.
a. Output. The use of the option is mandatory. The
classification level should be the dedicated level for dedicated
hosts and the system-high level for system-high and compartmented
hosts. The accrediting authority flags should be one for all
authorities which have accredited the hosts, and zero for all
other authorities.
b. Input. If 1) the option is present, 2) the classification
level matches the host classification level, and 3) the
accrediting authority flags for all accrediting authorities of the
receiving host are one, and all others are zero, the IP datagram
should be accepted for further processing. Otherwise, the out-
of-range procedure is followed.
9.3.15.3.4.3 Hosts accredited in the Multi-Level or Controlled Mode for
network transmission.
a. Output. The use of the option is mandatory. The
classification level of an IP datagram should be within the range
of levels for which the host is accredited. The protection
authorities flags should be one for all authorities under whose
rules the datagram should be protected.
b. Input. In the specific case where a multi-level or controlled
host is accredited to directly interface with an unclassified
environment, the host may accept IP datagrams without a basic
security option. Such datagrams should be assumed to be
implicitly labelled unclassified, GENSER, and should be so
labelled explicitly if they are later output. In all other cases,
the IP datagrams should have the basic security option on input,
and the out-of-range procedure should be followed if it is not.
There are two cases to be considered where the option is present.
The first case is where the system environment permits the values in
the option to be trusted to be correct for some range of values; the
second is where the values cannot be trusted to be correct. For each
multi-level or controlled host, every input channel for IP datagrams
must be considered and classed appropriately. If a channel does have
a trusted range, then the values of both the classification level and
the protection authorities are checked to insure that they fall
within that range and the range of accredited values for the
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receiving host. If within both ranges, the IP datagram is accepted
for further processing; otherwise the out-of-range procedure is
followed. If the label cannot be trusted, then the receiving host
must possess some accredited means of knowing what the correct
marking should be (e.g., a trusted channel to a system-high host at a
known level). On receipt of an IP datagram, the host compares the
actual values in the option to the correct values. If the values
match, the datagram is accepted for further processing; otherwise,
the out-of-range procedure is followed.
9.3.15.3.4.4 Out-Of-Range Procedure.
If an IP datagram is received which does not meet the input
requirements, then:
a) The data field should be overwritten with ones.
b) If the problem is a missing required Basic or Extended security
option, an ICMP "parameter problem" message is sent to the
originating host with the code field set to 1 (one) to indicate
"missing required option" and the pointer field set to the option
type of the missing option. Otherwise, an ICMP "parameter
problem" message is sent to the originating host with code field
set to 0 (zero) and with the pointer field pointing to the
position of the out-of-range security option.
c) If the receiving host has an interface to a local security
officer or equivalent, the problem should be identified across
that interface in an appropriate way.
9.3.15.3.4.5 Trusted Intermediary Procedure.
Certain devices in the internet may act as intermediaries to validate
that communications between two hosts are authorized, based on a
combination of knowledge of the hosts and the values in the IP
security option. These devices may receive IP datagrams which are in
range for the intermediate device, but are either not within the
acceptable range for the sender, or for the ultimate receiver. In
the former case, the datagram should be treated as described above
for an out-of-range option. In the latter case, a "destination
unreachable" ICMP message should be sent, with the code value of 10
(ten), indicating "Communication with Destination Host
Administratively Prohibited".
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9.3.15.4 DoD Extended Security Option
Option type: 133 Option length: variable
This option permits additional security related information, beyond
that present in the Basic Security Option, to be supplied in an IP
datagram to meet the needs of registered authorities. If this option
is required by an authority for a specific system, it must be
specified explicitly in any Request for Proposal. It is not
otherwise required. This option must be copied on fragmentation.
This option may appear multiple times within a datagram.
The format for this option is as follows:
+------------+-------------+-------------+--------//-------+
| 10000101 | 000LLLLL | AAAAAAAA | add sec info |
+------------+-------------+-------------+--------//-------+
type = 133 LENGTH = Var. ADDITIONAL ADDITIONAL
SECURITY SECURITY
INFO INFO
AUTHORITY
CODE
FIGURE 10-B.
9.3.15.4.1 Additional Security Info Authority Code.
length = 8 bits
The values of this field are assigned by DCA Code R130, Washington,
D.C. 20305-2000. Each value corresponds to a requestor who, once
assigned, becomes the authority for the remainder of the option
definition for that value.
9.3.15.4.2 Additional Security Information.
length - variable
This field contains any additional security information as specified
by the authority.
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BIT
NUMBER AUTHORITY
0 GENSER
1 SIOP
2 DSCCS-SPINTCOM
3 DSCCS-CRITICOM
4-7 Unassigned
AUTHORITY SOURCE OF ANNEX DESCRIBING
CURRENT CODING OF ADDITIONAL
SECURITY INFORMATION
GENSER
National Access Program, less SIOP Defense Communications
Agency
ATTN: Code R130
Washington, DC 20305
SIOP
National Access Program Department of Defense
Organization of the
Joint Chiefs of Staff
Attn: J6T
Washington, DC
DSCCS-SPINTCOM
National Access Program Defense Intelligence Agency
Attn: DSE4
Bolling AFB, MD
DSCCS-CRITICOM
National Access Program National Security Agency
9800 Savage Road
Attn: T03
Ft. Meade, MD 20755-6000
