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CIPSO Working Group
Internet Draft
1 November, 1991
COMMERCIAL IP SECURITY OPTION
Status of this Memo
This Internet Draft provides the high level specification for a Commercial
IP Security Option (CIPSO). This new option is meant to complement, not
replace, the existing IP security options and their successors. This draft
reflects the version as approved by the CIPSO IETF Working Group.
Distribution of this memo is unlimited.
1. Background
Currently the Internet Protocol includes two security options. One of
these options is the DoD Basic Security Option (BSO) (Type 130) which allows
IP datagrams to be labeled with security classifications. This option
provides sixteen security classifications and a variable number of handling
restrictions. To handle additional security information, such as security
categories or compartments, another security option (Type 133) exists and
is referred to as the DoD Extended Security Option (ESO). The values for
the fixed fields within these two options are administered by the Defense
Communications Agency (DCA).
Computer vendors are now building commercial operating systems with
mandatory access controls and multi-level security. These systems are
no longer built specifically for a particular group in the defense or
intelligence communities. They are generally available commercial systems
for use in a variety of government and civil sector environments.
The small number of ESO format codes can not support all the possible
applications of a commercial security option. The BSO and ESO were
designed to only support the United States DoD. CIPSO has been designed
to support multiple security policies. This Internet Draft provides the
format and procedures required to support a Mandatory Access Control
security policy. Support for additional security policies will be defined
in future RFCs.
2. CIPSO Format
Option type: 134 (Class 0, Number 6, Copy on Fragmentation)
Option length: Variable
This option permits security related information to be passed between
systems within a single Domain of Interpretation (DOI). A DOI is a
collection of systems which agree on the meaning of particular values
in the security option. An authority that has been assigned a DOI
identifier will define and distribute to hosts within the authority's
domain a mapping between appropriate CIPSO field values to their human
readable equivalent. These mappings may be sensitive, therefore a DOI
authority is not required to make these mappings available to anyone other
CIPSO IETF WORKING GROUP [PAGE 1]
CIPSO INTERNET DRAFT 1 November, 1991
than the systems that are included in the DOI.
This option MUST be copied on fragmentation. This option appears at most
once in a datagram. All multi-octet fields in the option are defined to be
transmitted in network byte order. The format of this option is as follows:
+----------+----------+------//------+-----------//---------+
| 10000110 | LLLLLLLL | DDDDDDDDDDDD | TTTTTTTTTTTTTTTTTTTT |
+----------+----------+------//------+-----------//---------+
TYPE=134 OPTION DOMAIN OF TAGS
LENGTH INTERPRETATION
Figure 1. CIPSO Format
2.1 Type
This field is 1 octet in length. Its value is 134.
2.2 Length.
This field is 1 octet in length. It is the total length of the option
including the type and length fields. With the current IP header length
restriction of 40 octets the value of this field will range from 6 to 40.
2.3 Domain of Interpretation Identifier
The length of this field is 4 octets. Its values are from 1-0xffffffff.
The value 0 is reserved and must not appear as the DOI identifier in any
CIPSO option. Implementations must assume that the DOI identifier field
is not aligned on any particular byte boundary.
To conserve space in the protocol, security levels and categories are
represented by numbers rather than their ASCII equivalent. This requires
a mapping table within CIPSO hosts to map these numbers to their
corresponding ASCII representations. Non-related groups of systems will
have their own unique mappings. For example, one group of systems may
use the number 5 to represent Unclassified while another group may use the
number 1 to represent that same security level. The DOI identifier is used
to identify which mapping was used for the values within the option.
2.4 Tag Types
A common format for passing security related information is necessary
for interoperability. In CIPSO the security related information is
defined to be a stream of tags that begin with a tag type identifier
followed by the length of the tag and ends with the actual security
information to be passed. All multi-octet fields in a tag are defined
to be transmitted in network byte order. Like the DOI identifier field
in the CIPSO header, implementations must assume that all tags, as well
CIPSO IETF WORKING GROUP [PAGE 2]
CIPSO INTERNET DRAFT 1 November, 1991
as fields within a tag, are not aligned on any particular octet boundary.
CIPSO tag types 0 through 127 are reserved for defining standard tag
formats and their definitions will be published in this and future RFCs.
Tag types whose identifiers are greater than 127 are defined by the DOI
authority and may only be meaningful in certain Domains of Interpretation.
For these tag types, implementations will require the DOI identifier as
well as the tag number to determine the security policy and the format
associated with the tag. Use of tag types above 127 are restricted to
closed networks where interoperability with other networks will not be an
issue.
Tag type 0 is reserved. Tag types 1, 2, and 5 are defined in this
Internet Draft. Types 3 and 4 are reserved for work in progress.
The standard format for all current and future CIPSO tags is shown below:
+----------+----------+--------//--------+
| TTTTTTTT | LLLLLLLL | IIIIIIIIIIIIIIII |
+----------+----------+--------//--------+
TAG TAG TAG
TYPE LENGTH INFORMATION
Figure 2: Standard Tag Format
In the three tag types described in this document, the length and count
restrictions are based on the current IP limitation of 40 octets for all
IP options. If the IP header is later expanded then the length and count
restrictions specified in this document may be assumed to increase to use
the full area provided for IP options.
2.4.1 Tag Type Classes
Tag classes consist of tag types that have common processing requirements
and support the same security policy. The three tags defined in this
Internet Draft belong to the Mandatory Access Control (MAC) Sensitivity
class and support the MAC Sensitivity security policy.
2.4.2 Tag Type 1
This is referred to as the "bit-mapped" tag type. Tag type 1 is included
in the MAC Sensitivity tag type class. The format of this tag type is as
follows:
+----------+----------+----------+----------+--------//---------+
| 00000001 | LLLLLLLL | 00000000 | LLLLLLLL | CCCCCCCCCCCCCCCCC |
+----------+----------+----------+----------+--------//---------+
TAG TAG ALIGNMENT SENSITIVITY BIT MAP OF
TYPE LENGTH OCTET LEVEL CATEGORIES
Figure 3. Tag Type 1 Format
CIPSO IETF WORKING GROUP [PAGE 3]
CIPSO INTERNET DRAFT 1 November, 1991
2.4.2.1 Tag Type
This field is 1 octet in length and has a value of 1.
2.4.2.2 Tag Length
This field is 1 octet in length. It is the total length of the tag type
including the type and length fields. With the current IP header length
restriction of 40 bytes the value within this field will be between 4
and 34.
2.4.2.3 Alignment Octet
This field is 1 octet in length and always has the value of 0. Its purpose
is to align the category bitmap field on an even octet boundary. This will
speed many implementations including router implementations.
2.4.2.4 Sensitivity Level
This field is 1 octet in length. Its value is from 0-255. The values are
assumed to be ordered with 0 being the minimum value and 255 representing
the maximum value.
2.4.2.5 Bit Map of Categories
The length of this field is variable and ranges from 0 to 30 octets. This
provides representation of categories 0 to 239. The ordering of the bits
is left to right or MSB to LSB. For example category 0 is represented by
the most significant bit of the first byte and category 15 is represented
by the least significant bit of the second byte. Figure 4 graphically
shows this ordering. Bit N is binary 1 if category N is part of the label
for the datagram, and bit N is binary 0 if category N is not part of the
label. Except for the optimized tag 1 format described in the next section,
minimal encoding SHOULD be used resulting in no trailing zero octets in the
category bitmap.
octet 0 octet 1 octet 2 octet 3 octet 4 octet 5
XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX . . .
bit 01234567 89111111 11112222 22222233 33333333 44444444
number 012345 67890123 45678901 23456789 01234567
Figure 4. Ordering of Bits in Tag 1 Bit Map
2.4.2.6 Optimized Tag 1 Format
Routers work most efficiently when processing fixed length fields. To
support networks that require high bandwidth routing there is an optimized
form of tag type 1. The format does not change. The only change is to the
category bitmap which is set to a constant length of 10 octets. Trailing
octets required to fill out the 10 octets are zero filled. Ten octets,
CIPSO IETF WORKING GROUP [PAGE 4]
CIPSO INTERNET DRAFT 1 November, 1991
allowing for 80 categories, was chosen because it makes the total length of
the CIPSO option 20 octets. If CIPSO is the only option then the options
field will be full word aligned and additional filler octets will not be
required.
2.4.3 Tag Type 2
This is referred to as the "enumerated" tag type. It is used to describe
large but sparsely populated sets of categories. Tag type 2 is in the MAC
Sensitivity tag type class. The format of this tag type is as follows:
+----------+----------+----------+----------+-------------//-------------+
| 00000010 | LLLLLLLL | 00000000 | LLLLLLLL | CCCCCCCCCCCCCCCCCCCCCCCCCC |
+----------+----------+----------+----------+-------------//-------------+
TAG TAG ALIGNMENT SENSITIVITY ENUMERATED
TYPE LENGTH OCTET LEVEL CATEGORIES
Figure 5. Tag Type 2 Format
2.4.3.1 Tag Type
This field is one octet in length and has a value of 2.
2.4.3.2 Tag Length
This field is 1 octet in length. It is the total length of the tag type
including the type and length fields. With the current IP header length
restriction of 40 bytes the value within this field will be between 4
and 34.
2.4.3.3 Alignment Octet
This field is 1 octet in length and always has the value of 0. Its purpose
is to align the category field on an even octet boundary. This will
speed many implementations including router implementations.
2.4.3.4 Sensitivity Level
This field is 1 octet in length. Its value is from 0-255. The values are
assumed to be ordered with 0 being the minimum value and 255 representing
the maximum value.
2.4.3.5 Enumerated Categories
In this tag, categories are represented by their actual value rather than
by their position within a bit field. The length of each category is 2
octets. Up to 15 categories may be represented by this tag. Valid values
for categories are 0-65534. Category 65535 is not a valid category value.
CIPSO IETF WORKING GROUP [PAGE 5]
CIPSO INTERNET DRAFT 1 November, 1991
The categories must be listed in the tag in ascending order.
2.4.4 Tag Type 5
This is referred to as the "range" tag type. It is used to represent
labels where all categories in a range, or set of ranges, are included
in the sensitivity label. Tag type 5 is in the MAC Sensitivity tag type
class. The format of this tag type is as follows:
+----------+----------+----------+----------+------------//-------------+
| 00000101 | LLLLLLLL | 00000000 | LLLLLLLL | Top/Bottom | Top/Bottom |
+----------+----------+----------+----------+------------//-------------+
TAG TAG ALIGNMENT SENSITIVITY CATEGORY RANGES
TYPE LENGTH OCTET LEVEL
Figure 6. Tag Type 5 Format
2.4.4.1 Tag Type
This field is one octet in length and has a value of 5.
2.4.4.2 Tag Length
This field is 1 octet in length. It is the total length of the tag type
including the type and length fields. With the current IP header length
restriction of 40 bytes the value within this field will be between 4
and 34.
2.4.4.3 Alignment Octet
This field is 1 octet in length and always has the value of 0. Its purpose
is to align the category range field on an even octet boundary. This will
speed many implementations including router implementations.
2.4.4.4 Sensitivity Level
This field is 1 octet in length. Its value is from 0-255. The values are
assumed to be ordered with 0 being the minimum value and 255 representing
the maximum value.
2.4.4.5 Category Ranges
Category ranges are pairs of 2 octet values that represent the top and
bottom of a category range respectively. These range endpoints are
inclusive within the range of categories. All categories within a range
are assumed to be included in the sensitivity label. This tag may contain
a maximum of 7 category pairs. The bottom category endpoint for the last
pair in the tag may be omitted and will be assumed to be 0. The ranges
CIPSO IETF WORKING GROUP [PAGE 6]
CIPSO INTERNET DRAFT 1 November, 1991
must be non-overlapping and be listed in descending order.
2.4.5 Minimum Requirements
A CIPSO implementation MUST be capable of generating at least tag type 1 in
the non-optimized form. In addition, a CIPSO implementation MUST be able
to receive any valid tag type 1 even those using the optimized tag type 1
format.
3. Configuration Parameters
The configuration parameters defined below are required for all CIPSO hosts,
gateways, and routers that support multiple sensitivity labels. A CIPSO
host is defined to be the origination or destination system for an IP
datagram. A CIPSO gateway provides IP routing services between two or more
IP networks and may be requiremented to perform label translations between
networks. A CIPSO gateway may be an enhanced CIPSO host or it may just
provide gateway services with no end system CIPSO capabilities. A CIPSO
router is a dedicated IP router that routes IP datagrams between two or more
IP networks.
An implementation of CIPSO on a host must have the capability to reject a
datagram for reasons that the information contained can not be adequately
protected by the receiving host or if acceptance may result in violation of
the host or network security policy. In addition, a CIPSO gateway or router
must be able to reject datagrams going to networks that can not provide
adequate protection or may violate the network's security policy. To
provide this capability the following minimal set of configuration
parameters are required for CIPSO implementations:
HOST_LABEL_MAX - This parameter contains the maximum sensitivity label that
a CIPSO host is authorized to handle. All datagrams that have a label greater
than this maximum must be rejected by the CIPSO host. This parameter does
not apply to CIPSO gateways or routers. This parameter need not be defined
explicitly as it can be implicitly derived from the PORT_LABEL_MAX
parameters for the associated interfaces.
HOST_LABEL_MIN - This parameter contains the minimum sensitivity label that
a CIPSO host is authorized to handle. All datagrams that have a label less
than this minimum must be rejected by the CIPSO host. This parameter does
not apply to CIPSO gateways or routers. This parameter need not be defined
explicitly as it can be implicitly derived from the PORT_LABEL_MIN
parameters for the associated interfaces.
PORT_LABEL_MAX - This parameter contains the maximum sensitivity label for
all datagrams that may exit a particular network interface port. All
outgoing datagrams that have a label greater than this maximum must be
rejected by the CIPSO system. The label within this parameter will be less
than or equal to the label within the HOST_LABEL_MAX parameter. This
parameter does not apply to CIPSO hosts that support only one network port.
PORT_LABEL_MIN - This parameter contains the minimum sensitivity label for
all datagrams that may exit a particular network interface port. All
CIPSO IETF WORKING GROUP [PAGE 7]
CIPSO INTERNET DRAFT 1 November, 1991
outgoing datagrams that have a label less than this minimum must be
rejected by the CIPSO system. The label within this parameter will be
greater than or equal to the label within the HOST_LABEL_MIN parameter.
This parameter does not apply to CIPSO hosts that support only one network
port.
PORT_DOI - This parameter is used to assign a DOI identifier value to a
particular network interface port. All CIPSO labels within datagrams
going out this port will use the specified DOI identifier. All CIPSO hosts
and gateways will support either this parameter, the NET_DOI parameter, or
the HOST_DOI parameter.
NET_DOI - This parameter is used to assign a DOI identifier value to a
particular IP network address. All CIPSO labels within datagrams destined
for the particular IP network will use the specified DOI identifier. All
CIPSO hosts and gateways will support either this parameter, the PORT_DOI
parameter, or the HOST_DOI parameter.
HOST_DOI - This parameter is used to assign a DOI identifier value to a
particular IP host address. All CIPSO labels within datagrams destined for
the particular IP host will use the specified DOI identifier. All CIPSO
hosts and gateways will support either this parameter, the PORT_DOI
parameter, or the NET_DOI parameter.
This list represents the minimal set of configuration parameters required
to be compliant. Implementors are encouraged to add to this list to
provide enhanced functionality and control. For example, many security
policies may require both incoming and outgoing datagrams be checked against
the port and host label ranges.
3.1 Port Range Parameters
The labels represented by the PORT_LABEL_MAX and PORT_LABEL_MIN parameters
may be in CIPSO or local format. Some CIPSO systems, such as routers, may
want to have the range parameters expressed in CIPSO format so that incoming
labels do not have to be converted to a local format before being compared
against the range. If multiple DOIs are supported by one of these CIPSO
systems then multiple port range parameters would be needed, one set for
each DOI supported on a particular port.
The port range will usually represent the total set of labels that may
exist on the logical network accessed through the corresponding network
interface. It may, however, represent a subset of these labels that are
allowed to enter the CIPSO system.
3.2 Single Label CIPSO Hosts
CIPSO implementations that support only one label are not required to
support the parameters described above. These limited implementations are
only required to support a NET_LABEL parameter. This parameter contains
the CIPSO label that may be inserted in datagrams that exit the host. In
addition, the host must reject any incoming datagram that has a label which
is not equivalent to the NET_LABEL parameter.
CIPSO IETF WORKING GROUP [PAGE 8]
CIPSO INTERNET DRAFT 1 November, 1991
4. Handling Procedures
This section describes the processing requirements for incoming and
outgoing IP datagrams. Just providing the correct CIPSO label format
is not enough. Assumptions will be made by one system on how a
receiving system will handle the CIPSO label. Wrong assumptions may
lead to non-interoperability or even a security incident. The
requirements described below represent the minimal set needed for
interoperability and that provide users some level of confidence.
Many other requirements could be added to increase user confidence,
however at the risk of restricting creativity and limiting vendor
participation.
4.1 Input Procedures
All datagrams received through a network port must have a security label
associated with them. Without this label the host, gateway, or router
will not have the information it needs to make security decisions.
This security label will be obtained from the CIPSO if the option is
present in the datagram. See section 4.1.2 for handling procedures for
unlabeled datagrams. This label will be compared against the PORT
(if appropriate) and HOST configuration parameters defined in section 3.
If any field within the CIPSO option, such as the DOI identifier, is not
recognized the IP datagram is discarded and an ICMP "parameter problem"
(type 12) is generated and returned. The ICMP code field is set to "bad
parameter" (code 0) and the pointer is set to the start of the CIPSO field
that is unrecognized.
If the contents of the CIPSO are valid but the security label is
outside of the configured host or port label range, the datagram is
discarded and an ICMP "destination unreachable" (type 3) is generated
and returned. The code field of the ICMP is set to "communication with
destination network administratively prohibited" (code 9) or to
"communication with destination host administratively prohibited"
(code 10). The value of the code field used is dependent upon whether
the originator of the ICMP message is acting as a CIPSO host or a CIPSO
gateway. The recipient of the ICMP message must be able to handle either
value.
If the error is triggered by receipt of an ICMP message, the message
is discarded and no response is permitted (consistent with general ICMP
processing rules).
4.1.1 Unrecognized tag types
The default condition for any CIPSO implementation is that an
unrecognized tag type will be treated as a "parameter problem" and
handled as described in section 4.1. A CIPSO implementation may allow
the system administrator to identify tag types that may safely be
ignored. This capability is an allowable enhancement, not a
CIPSO IETF WORKING GROUP [PAGE 9]
CIPSO INTERNET DRAFT 1 November, 1991
requirement.
4.1.2 Unlabeled Packets
A network port may be configured to not require a CIPSO label for all
incoming datagrams. For this configuration a CIPSO label must be
assigned to that network port and associated with all unlabeled IP
datagrams. This capability might be used for single level networks or
networks that have CIPSO and non-CIPSO hosts and the non-CIPSO hosts
all operate at the same label.
If a CIPSO option is required and none is found, the datagram is
discarded and an ICMP "parameter problem" (type 12) is generated and
returned to the originator of the datagram. The code field of the ICMP
is set to "option missing" (code 1) and the ICMP pointer is set to 134
(the value of the option type for the missing CIPSO option).
4.2 Output Procedures
A CIPSO option may appear only once in a datagram. Only one tag type
from the MAC Sensitivity class may be included in a CIPSO option. Given
the current set of defined tag types, this means that CIPSO labels at
first will contain only one tag. Compliant CIPSO implementations must be
able to support multiple tags within a CIPSO option.
All datagrams leaving a CIPSO system must meet the following condition:
PORT_LABEL_MIN <= CIPSO label <= PORT_LABEL_MAX
If this condition is not satisfied the datagram must be discarded.
If the CIPSO system only supports one port, the HOST_LABEL_MIN and the
HOST_LABEL_MAX parameters may be substituted for the PORT parameters in
the above condition.
The DOI identifier to be used for all outgoing datagrams is configured by
the administrator. If port level DOI identifier assignment is used, then
the PORT_DOI configuration parameter will contain the DOI identifier to use.
If network level DOI assignment is used, then the NET_DOI parameter will
contain the DOI identifier to use. And if host level DOI assignment is
employed, then the HOST_DOI parameter will contain the DOI identifier to
use. A CIPSO implementation need only support one level of DOI assignment.
4.3 DOI Processing Requirements
A CIPSO implementation MUST support at least one DOI and SHOULD support
multiple DOIs. System and network administrators are cautioned to
ensure that at least one DOI is common within an IP network to allow for
broadcasting of IP datagrams.
CIPSO gateways must be capable of translating a CIPSO option from one
DOI to another when forwarding datagrams between networks. For
efficiency purposes this capability is only a desired feature for CIPSO
CIPSO IETF WORKING GROUP [PAGE 10]
CIPSO INTERNET DRAFT 1 November, 1991
routers.
4.4 Label of ICMP Messages
The CIPSO label to be used on all outgoing ICMP messages will be equivalent
to the label of the datagram that caused the ICMP message. If the ICMP was
generated due to a problem associated with the original CIPSO label then the
following responses are allowed:
a. Use the CIPSO label of the original IP datagram
b. Drop the original datagram with no return message generated
In most cases these options will have the same effect. If you can not
interpret the label or if it is outside the label range of your host or
interface then an ICMP message with the same label will probably not be
able to exit the system.
5. Assignment of DOI Identifier Numbers
Requests for assignment of a DOI identifier number should be addressed to
the Internet Assigned Numbers Authority (IANA).
6. Acknowledgements
Much of the material in this RFC is based on (and copied from) work
done by Gary Winiger of Sun Microsystems and published as Commercial
IP Security Option at the INTEROP 89, Commercial IPSO Workshop.
7. Author's Address
To submit mail for distribution to members of the IETF CIPSO Working
Group, send mail to: cipso@wdl1.wdl.loral.com.
To be added to or deleted from this distribution, send mail to:
cipso-request@wdl1.wdl.loral.com.
8. References
RFC 1038, "Draft Revised IP Security Option", M. St. Johns, IETF, January
1988.
Internet Draft AHWGIPSO-1, "U.S. Department of Defense Security Options
for the Internet Protocol", Stephen Kent, IAB, 1 March, 1991.
CIPSO IETF WORKING GROUP [PAGE 11]