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⟦60eb74923⟧ Wang Wps File
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Names: »~ORPHAN51.01«
Derivation
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WangText
te than normal transmission speed.
TDG Test Data Generator
Validation The act of checking a message for
validity.
Message, Legal A message which is allowed to pass
the security filter.
Message, Illegal A message which is not allowed o
pass the security filter.
Message, Validated A message which has been subject
to
validation.
Message, Accepted A message which by the validation
has been found to be legal.
Message, Rejected A message which by the validation
has been fund to be illegal.
Message, Logged A rejected message which has been
written onto the logging medium.
Message, Suspended A message which by its type or contents
or otherwise demands operator assisted
validation and hence has been stored
fo this purpose.
2 S̲U̲M̲M̲A̲R̲Y̲ ̲O̲F̲ ̲R̲E̲Q̲U̲I̲R̲E̲M̲E̲N̲T̲S̲
2.1 S̲Y̲S̲T̲E̲M̲ ̲D̲E̲S̲C̲R̲I̲P̲T̲I̲O̲N̲
The Security Filter is an electronic device (computer)
placed on a point-to-point communication line connecting
two ADP-sysems of unequal security classification,
with
the purpose of filtering the message traffic, i.e.
to withhold messages which for security reasons are
not allowed to pass the subject communication line.
The security filter operates on traffic both ays but
with different filter characteristics.
The messages which shall be withheld are not only those
which are classified higher than the receiving ADP-
system but also messages containing information outside
the receiving system's scope of "ned to know".
To achieve this goal it is necessary to provide full
and positive description of this "need to know", so
that the security filter will only allow messages to
pass if they are positively identified as containing
only such information.
Alert
ADP Security ADP
System Filter System
Log
Fundamentally, the security filter is aimed at automated
operation without any human intervention. This requires,
however, that the traffic consists solely of well structured
messges with a predictable set of contents. If the
traffic on a line is expected to also contain unstructured
messages or free text, which cannot be automatically
analyzed, human support may be introduced as an option.
Even though the concept of a seurity filter originally
is aiming at a separate filter for each point-to-point
line it may be considered to develop a multiline security
filter, or to share hardware, software, or peripherals
among a number of security filters, to achieve cost
effetive operation. The design of such a multiline
system would need to provide for the additional security
required to keep messages separate and to ensure their
proper delivery.
2.2 S̲Y̲S̲T̲E̲M̲ ̲F̲U̲N̲C̲T̲I̲O̲N̲S̲
2.2.1 F̲i̲l̲t̲e̲r̲ ̲F̲u̲n̲c̲t̲i̲o̲n̲s̲
The filter characterstics are implemented by means
of a definition of all legal messages and their contents.
The security filter software (computer programs) shall
be so constructed that any foreseeable change in message
structure and contents can be handled without mdification
of the software.
As a consequence of the definition of all legal traffic,
any message traffic deviating from the definition shall
be considered illegal and handled in accordance with
that condition.
Illegal messages shall be logged b the security filter
and may not be transmitted from the filter. In case
of frequent traffic of illegal messages (frequency
exceeding a prespecified maximum) an audible alert
shall be sounded in order to inform the security officer
of this fact.
To expand the useful scope of the security filter to
encompass lines where the traffic will contain messages
too complex for automatic validation operator communication
facilitiescan be added. This will allow for human validation
of for instance free text messages. However, message
types or message contents demanding human validation
shall be defined to the filter. The display of a message
for an operator must never be trigered by the fact
that the message is considered illegal by the automatic
validation.
2.2.2 A̲u̲x̲i̲l̲i̲a̲r̲y̲ ̲F̲u̲n̲c̲t̲i̲o̲n̲s̲
The security filter shall be operative without any
human intervention, and it shall be possible to modify
neither software nor messaes on site while the filter
operates.
Hence, any authorized modification must be performed
off-line and installed afterwards on the filter site
following a prespecified procedure.
The following auxiliary functions to be performed off-line
have een identified:
2.2.2.1 S̲o̲f̲t̲w̲a̲r̲e̲ ̲P̲r̲o̲d̲u̲c̲t̲i̲o̲n̲ ̲a̲n̲d̲ ̲M̲a̲i̲n̲t̲e̲n̲a̲n̲c̲e̲
The computer programs necessary to perform the security
filter functions must be analyzed, planned, documented,
coded, compiled, tested and verified.
Since the security filter by it
