Security engineering Flashcards
Tow modes of Operation of Operating system
supervisor state (Privileged mode) problem state(User mode)
system call ?
The mechanism whereby mediated access occurs—that is, the driver or handler
request mentioned previously—is usually known as a system call and usually involves
invocation of a specific system or programming interface designed to pass the request to
an inner ring for service.
Ready State
In the ready state, a process is ready to resume or begin processing as soon as it
is scheduled for execution.
This means the process has all the memory and other resources it needs
to begin executing immediately.
Waiting
Waiting can also be understood as “waiting for a resource”—that is, the process
is ready for continued execution but is waiting for a device or access request
Running
The running process executes on the CPU and keeps going until it finishes, its
time slice expires, or it is blocked for some reason
The running state is also often called the problem state
it is
called the problem state because it is possible for problems or errors to occur
process scheduler
A special part of the kernel, called the program executive or the
process scheduler, is always around (waiting in memory) so that when a process state
transition must occur, it can step in and handle the mechanics involved.
The US government has designated four approved security modes for
systems that process classified information.
Dedicated Mode
System High Mode
Compartmented mode
Multilevel Mode
Dedicated Mode
Each user must have a security clearance (access to all information processed by the system.)
Each user must have access approval (all information processed by the system)
Each user must have a valid need to know (all information processed by the
system.)
System High Mode
Each user must have a valid security clearance (access to all information processed by the system.)
Each user must have access approval (all information processed by the system)
*Each user must have a valid need to know for some information but not necessarily all information processed by the system
Compartmented mode
Each user must have a valid security clearance (access to all informationprocessed by the system.)
*Each user must have access approval for any information they will have access to on the system.
Each user must have a valid need to know (all information they will have access to
on the system.)
difference between compartmented mode systems and system high
mode systems
users of a compartmented mode system do not necessarily have
access approval for all the information on the system. However, as with system high and
dedicated systems, all users of the system must still have appropriate security clearances
Multilevel Mode
*Some users do not have a valid security clearance for all information processed by
the system. Thus, access is controlled by whether the subject’s clearance level
dominates the object’s sensitivity label.
Each user must have access approval for all information they will have access to on
the system.
Each user must have a valid need to know for all information they will have access to
on the system.
Note
Mode Clearance Need to know PDMCL
Dedicated Same None None
System high Same Yes None
Compartmented Same Yes Yes
Multilevel Different Yes Yes
Clearance is Same if all users must have the same security clearances, Different if otherwise.
Need to Know is None if it does not apply and is not used or if it is used but all users have the need to know all data
present on the system, Yes if access is limited by need-to-know restrictions.
PDMCL applies if and when CMW implementations are used (Yes); otherwise, PDMCL is None.
notice that the administrative requirements for controlling the
types of users that access a system decrease as you move from dedicated systems down to
multilevel systems.
2)
When comparing all four security modes, it is generally
understood that the multilevel mode is exposed to the highest level of risk.
ROM’s primary advantage ?
ROM’s primary advantage is that it can’t be modified
Programmable Read-Only Memory (PROM)
PROM chip’s contents aren’t “burned in” at the
factory as with standard ROM chips. Instead, a PROM incorporates special functionality
that allows an end user to burn in the chip’s contents later. However, the burning process
has a similar outcome—once data is written to a PROM chip, no further changes are
possible. After it’s burned in, a PROM chip essentially functions like a ROM chip.
PROM Commonly used ?
PROMs are commonly used for
hardware applications where some custom functionality is necessary but seldom changes
once programmed.
EPROM
when illuminated with a special
ultraviolet light, causes the contents of the chip to be erased. After this process is
complete, end users can burn new information into the EPROM as if it had never been
programmed before.
EEPROM
uses electric voltages delivered to the
pins of the chip to force erasure. EEPROM chips can be erased without removing them
from the computer, which makes them much more attractive than standard PROM or
EPROM chips.
Flash Memory
Flash memory is a derivative concept from EEPROM.
It is a nonvolatile
form of storage media that can be electronically erased and rewritten. The primary
difference between EEPROM and flash memory is that EEPROM must be fully erased to
be rewritten whereas flash memory can be erased and written in blocks or pages.
most common type of flash memory is NAND flash
It is widely used in memory cards,
thumb drives, mobile devices, and SSD (solid-state drives).
Real memory
known as main memory or primary memory
is
typically the largest RAM storage resource available to a computer. It is normally
composed of a number of dynamic RAM chips and, therefore, must be refreshed by the
CPU on a periodic basis
Cache RAM
caches that improve performance
by taking data from slower devices and temporarily storing it in faster devices when
repeated use is likely; this is cache RAM.
dynamic RAM
uses a series of capacitors, tiny electrical devices that
hold a charge
However, because capacitors naturally
lose their charges over time, the CPU must spend time refreshing the contents of
dynamic RAM to ensure that 1 bits don’t unintentionally change to 0 bits, thereby
altering memory contents.
Static RAM uses more sophisticated technology
a logical device known as a flip-flop,
which to all intents and purposes is simply an on/off switch that must be moved
from one position to another to change a 0 to 1 or vice versa. More important, static
memory maintains its contents unaltered as long as power is supplied and imposes
no CPU overhead for periodic refresh operations.
registers
(ALU), uses when performing calculations or processing
instructions
operates in lockstep with the
CPU at typical CPU speeds.