What are different modes of unauthorized access?

You or your company might have a number of resources that you might need to protect from unauthorized people and ensure that only people who have a right to access these resources can access and use them. These resources might be either personnel, physical or informational. All this is done using access control. It is not just about creating user names and passwords whenever resources have to be accessed. There are many models, techniques, methods that can be implemented to maintain security. Also there are a number of types of attacks against each type of the distinct methods. In the process of authorization, access is granted to the authenticated subjects. It involves carrying out specific operations based up on the predefined access rights mentioned in the access criteria. This criterion is based up on the following factors:
- Clearance: Security level of the subject.
- Need – to – know: The approved formal access level.
Attackers employ a number of tricks and techniques for gaining unauthorized access to the resources and information of the company. Necessary countermeasures need to be taken so that these threats can be identified and eliminated.
There are different modes of unauthorized access as discussed further:
- Unauthorized disclosure of information: The disclosure of sensitive information might be intentional or accidental. Whatever the cause maybe, the results are always same. The individual get the information that they were not intended to access. A large part of the access control is about preventing such types of incidents from taking place. People might use different kinds of media for sharing information around the organization such as hard drives, floppy disks, shares on servers and so on. These media might contain sensitive information that might get in to the hand of the people for which it is not intended. Also new employees might be assigned old computers to work up on which might also contain some sensitive information stored by the former employees. Object reuse is one example where some object containing sensitive information might be used by other subjects.
- Emanation security: Attackers can even intercept electrical signals for stealing the information. The signals are radiated by the computers and other devices which can be intercepted by attackers by means of some specialized equipment. Using the right software as well as hardware, this information can be reconstructed without coming into the knowledge of the users using it. Main countermeasures include control zones, white noise and the TEMPEST.
- Man – in – the – middle attacks: An intruder drops in to a conversation going on between two hosts and intercepts the messages. Sequence numbers and digital signals can be used as countermeasures.
- Sniffing: This is a type of passive attack when the network is monitored by the intruder for gaining info concerning the victim and is used for attacking later. Data encryption can be done for preventing all this.
- War dialing: This is a kind of brute force attack where a program is used by the attacker using which it dials a large bank of phone numbers. This is done to check which phone belongs to a particular modem. Using this, the attacker can gain access to the network. Not publicizing telephone numbers is one countermeasure.
- Ping of death: In this Denial – of – service attack, the attacker sends oversized ICMP packets to the victim host. If the host is not familiar with how to handle such large packets, it may reboot or freeze. Implementing ingress filtering and patching the systems are some counter measures for detecting such oversized ICMP packets. Another type of DoS attack is the WinNuk.

What is Wifi technology? How does it work?

- Wifi has emerged as a very popular technology. 

- This technology has enabled the electronic devices to exchange information between them and to share the internet connection without using any cables or wires. 

- It is a wireless technology. 

- This technology works with the help of the radio waves. 

- The Wifi is defined as a WLAN (wireless local area network) product by the wifi alliance that is based on the standards defined by IEEE (802.11 standards). 

- Most of the WLANs are based upon these standards only and so this technology has been named as wifi which is the synonymous with the term WLAN. 

- The wifi-certified trademark might be used by only those wifi products which have the complete certification for the wifi alliance inter-operability. 

- A number of devices now use wifi such as the PCs, smart phones, video game consoles, digital cameras, digital audio players, tablet computers and so on. 

- All these devices can connect to the network and access internet by means of a wireless network access point. 

- Such an access point is more commonly known as a ‘hotspot’. 

- The range of an access point is up to 20 m. 

- But it has a much greater range outside.  

- An access point can be installed in a single room or in an area of many square miles. 

- This can be achieved by using a number of overlapping access points. 

- However, the security of the wifi is less compared to the wired connections for example Internet.

- This is so because a physical connection is not required by an intruder. 

- The web pages using SSL have security but the intruders can easily access the non-encrypted files on the internet. 

- It is because of this, that the various encryption technologies have been adopted by the wifi. 

- The earlier WEP encryption was weak and so was easy to break.

- Later, came the higher quality protocols such as the WPA2 and WPA. 

- The WPS or the wifi protected set up was an optional feature that was added in the year of 2007. 

- This option a very serious flaw which is that it allowed the recovery of the password of the router by an attacker.

- The certification and the test plan has been updated by the wifi alliance for ensuring that there is resistance against attacks in all the devices that have been newly certified.

- For connecting to a wifi LAN, a wireless network interface controller has to be incorporated in to the computer system.

- This combination of the interface controller and the computer is often called as the station. 

- The same radio frequency communication channel is shared by all the stations.

- Also, all the stations receive any transmission on this channel. 

- Also, the user is not informed of the fact that the data was delivered to the recipient and so is termed as the ‘best–effort delivery mechanism’. 

- For transmitting the data packets, a carrier wave is used. 

- These data packets are commonly known as the ‘Ethernet frames’. 

- Each station regularly tunes in to the radio frequency channel for picking up the transmissions that are available. 

- A device that is wifi enabled can connect to the network if it lies in the range of the wireless network. 

- One condition is that the network should have been configured for permitting such a connection. 

- For providing coverage in a large area multiple hotspots are required. 

- For example, wireless mesh networks in London. 

- Through wifi, services can be provided in independent businesses, private homes, public spaces, high street chains and so on. 

- These hotspots have been set up either commercially or free of charge. 

- Free hotspots are provided at hotels, restaurants and airports. 

What properties are common between WDMA and GSM channel access protocols?

About Wavelength Division Multiplexing Access(WDMA)

- Wavelength division multiplexing access or WDMA is a concept of fiber optics communications that is all about multiplexing the number of optical carrier signals in to one optical fiber. 

- This is done by using a number of different wavelengths or colors of the LASER lights. 

- This technique has made it possible to make bidirectional communications through one fiber strand and multiplication of capacity.

- The frequency division multiplexing is applied to radio carrier whereas this WDMA is used in the optical fibers. 

- An inverse relationship ties the frequency and wavelength together since the same concept is described by the two terms. 

- WDMA is classified under channel access methods and is based on wavelength division multiplexing. 

- A system using the WDM consists of a multiplexer at the transmitting end for joining the signals together. 

- Similarly, a de-multiplexer is installed at the receiver’s end.

- The de-multiplexer is used for splitting the joined signal apart.

- It is possible to make a device using the right kind of fiber that can do both multiplexing and de-multiplexing simultaneously as well as an optical add – drop multiplexer.

About Global System for Mobile Communications(GSM)

- Global system for mobile communications is an ETSI (European telecommunications standards institute) developed standard set for describing the protocols for 2G i.e., second generation mobile networks. 

- This standard set now rules the market with around 80 percent of the total market share. 

- GSM describes a digital network operating on circuit switching and that has been optimized for full duplex voice telephony. 

- GSM means a cellular network. 

- For connecting to this network, the cell phone searches for other cells in its surrounding. 

- GSM network offers 5 types of different cell sizes namely:

1. Macro
2. Micro
3. Pico
4. Femto
5. Umbrella cells

- The extent of the area covered by each of the cells varies depending on the environment in which they are being implemented. 

- The base antenna is installed in the macro cells as a mast.

- In the micro cells, the height of the antenna is at the average level of the roof top. 

- Pico cells have a coverage diameter of only few meters.

- Femto cells find use in the small business and residential environments. 

- They are used for connecting to the ISP’s network. 

- Shadowed regions of the cells which are small are covered by the umbrella cells.

Common Properties and Differences between WDMS and GSM

Usually there are a number of differences between GSM and WDMA but they share some common properties also. 
- The base station of the GSM system and that of the WDMA both are connected to the core network of the GSM system in order to facilitate radio connectivity in the handsets. 
- Therefore, the same core network is shared by both the technologies. 
- Principles of the cellular radio system form the basis for the two technologies. 
- There exists a correspondence between the WDMA radio network controller i.e., RNC and the GSM base station controller or BSC. 
- The RBS (radio base station) of GSM system corresponds to the RBS of the WDMA. 
- The basis for developing the lu – interface of WDMA was provided by the A-interface of the GSM technology. 
- The only difference is of the new additional services that are offered by the WDMA. 
- GSM makes use of time division multiplexing along with the radio functionality for the management of the time slots. 
- On the other hand, WDMA makes use of the code division multiplexing for the same. 
- This implies that the control as well as the hardware functions of both are different

Explain Carrier Sense Multiple Access Protocols - CSMA

- CSMA or Carrier Sense Multiple Access is defined as a probabilistic MAC (media access control) protocol. 

- In this protocol the absence of the traffic is verified by the node prior to start transmitting through a transmission medium that is shared by a number of channels. 

- For example, a band of EM spectrum, electric bus and so on. 

- Feedback from the receiver is used by the transmitter for determining whether the channel is already occupied by some transmission process or not. - This is termed as the carrier sense. 

- The transmitter before starting a transmission starts detecting whether a carrier wave is present their transmitted by some another station. 

- If a carrier wave is present, the transmission has no other option other than waiting for the transmission in progress to end before starting its own transmission. 

- To put it simply we can say that the carrier sense is what the CSMA protocol is based up on. 

- By ‘multiple access’, it simply means that a number of stations can transmit and receive data through the same medium. 

- But in this case all the other stations receive the data transmitted by one node using that same medium. 

There are many types of CSMA protocols as mentioned below:

1. CSMA with collision detection: 

- In short, this protocol is known as the CSMA/CD. 

- This protocol is used for improving the performance. 

- This it does through the termination of the transmission once a collision occurs along making reductions in the probability of occurrence of the other collisions upon re-transmissions.

2. CSMA with collision avoidance: 

- CSMA/ CA is the abbreviated form of this type of CSMA protocol. 

- This protocol avoids collision for improving the performance of the same.

- It tends not to be greedy on the transmitting channel.

- If it happens to sense the channel as busy prior to transmission then it is said to defer to a random interval.

- This is a measure for reduction in the probability of the packet collisions occurring on the channel.

3. Virtual time CSMA: 

- In short, known as the VTCSMA.

- This type of CSMA protocol has been designed for avoiding the collisions that are generated by the nodes. 

- These are the nodes that translate the signals at the same time. 

- This CSMA protocol is employed in the hard real time systems. 

- Two clocks are used by each node namely a real clock (rc) and a virtual clock (vc) for telling ‘real time’. 

- If the channel happens to be busy, the virtual clock freezes and if not it is reset. 

- vc is not initialized if the channel is busy and it runs faster when compared to the real clock.

CSMA happens to operate in various modes as discussed below:

1-Persistent: 

- The sender stations keeps on sensing the transmission channel until it becomes idle if previously it was busy. 

- When it finally becomes, then it starts transmitting the data packet i.e., the frame. 

- If a collision is detected, the transmitter has to wait for a random period of time before attempting to re-transmit the signal. 

- It finds use in systems such as Ethernet i.e., the systems using CSMA/ CD.

P-Persistent: 

- This mode lies somewhere between the non–persistent and the 1–persistent CSMA access modes.

- Once the data is ready to be transmitted, it checks for the status of the medium and starts transmitting the data packets with a certain probability.

Non-persistent: 

Less aggressive when compared to the previous one.

O-Persistent:

It works based according to the assigned transmission order. 

Explain the various File Access methods?

One of the most important functions of the mainframe operating system is the access methods that make it possible for you to access the data from external devices such as the tape or disk. 

What are access methods?

- Access methods are very useful in providing an API for transferring the data from one device to another.

- Another best thing about this API was that it worked as the device driver for the operating systems on non-mainframe computers. 

- There have been a lot of reasons behind the introduction of the access methods. 

- A special program had to be written for the I/O channel and there has to be a processor entirely dedicated to controlling the access to the peripheral storage device as well as data transfer from and to the physical memory. 

- Special instructions constitute these channel programs and are known as the CCWs or the channel command words.

- To write such programs, very detailed knowledge is required regarding the characteristics of the hardware. 

Benefits of File Access Methods

There are 3 major benefits of the file access methods:

Ø  Ease of programming: The programmer does not have to deal with the procedures of the specific devices, recovery tactics and error detection. A program designed to process a particular thing will do it no matter where the data has been stored.

Ø  Ease of hardware replacement: A program cannot be altered by the programmer during the migration of data from older to newer model of the storage device provided the same access methods are supported by the new model.

Ø  Ease in sharing the data set access: The access methods can be trusted for managing the multiple accesses to the same file. At the same it ensures the security of the system and data integrity.

Some File/Storage Access Methods

Ø  Basic direct access method (BDAM)

Ø  Basic sequential access method (BSAM)

Ø  Queued sequential access method (QSAM)

Ø  Basic partitioned access method (BPAM)

Ø  Indexed sequential access method (ISAM)

Ø  Virtual storage access method (VSAM)

Ø  OAM (object access method)

- For dealing with the records of a data set both the types of access i.e., the queued and the basic are suitable. 

- The queued access methods are an improvement of the basic file access methods. 

- Read ahead scheme and internal blocking of data is well supported by these methods. 

- This allowed combining the multiple records in to one unit, thus increasing the performance. 

- In sequential methods, it is assumed that there’s only a sequential way for processing the records which is just the opposite of the direct access methods. 

- There are devices like the magnetic tape that only enforce the sequential access 

- Sequential access can be used for writing a data set and then later the direct manner can be used for processing it.

Today we have access methods that are network-oriented such as the following:

Ø  Basic telecommunications access method or BTAM

Ø  Queued tele – processing access method or QTAM

Ø  Telecommunications access method or TCAM

Ø  Virtual telecommunications access method or VTAM

- The term access method was used by the IMS or the IBM information management system for referring to the methods for manipulation of the database records. 

- The access methods used by them are:

Ø  GSAM or generalized sequential access method

Ø  HDAM or hierarchical direct access method

Ø  HIDAM or hierarchical indexed direct access method

Ø  HISAM or hierarchical indexed sequential access method

Ø  HSAM or hierarchical sequential access method

Ø  PHDAM or partitioned hierarchical direct access method

Ø  PHIDAM or partitioned hierarchical indexed direct access

What is hard disk and what is its purpose?

- HDD or Hard Disk Drive is for data storage. 

- It is used for storage and retrieval of the digital information or data that is stored on it. 

- The data is stored or retrieved by means of its discs that rotate rapidly. 

Hard Disk and its Purpose

 

- These discs are known as the platters and are coated with some sort of magnetic material. 

- The major characteristic as well as benefit of hard disk drives is that they retain the data even when the power supply is switched off. 

- From hard disk, the data can be read in a manner of random access. 

- This means that the storing and retrieval of the individual blocks of the data can be done either sequentially or in any order that the user may like. 

- A hard disk may consist of one or more than one of those rigid platters. 

- These rotating discs have magnetic heads that are located on an actuator arm that is continuously moving and reads and writes data on their surfaces. 

- IBM was the first to introduce the hard disk in the year of 1956. 

- Hard disk drives are the most dominant and the prominent secondary storage device for the computers since 1960s. 

- Since then, it has been continuously improved. 

- The HDD units are produced by more than 200 companies; among them most prominent developers are Toshiba, Seagate, Western digital etc. 

HDD’s primary characteristics are:

Ø  Capacity and

Ø  Performance

- The former is specified in terms of the unit prefixes. 

- In some systems, the capacity of the hard disk drive might be unavailable to the user since being used by the operating system and the file system and may have a possibility of occurrence of redundancy.

- The latter is specified in terms of the movements of the heads for a file i.e., the average access time in addition to the time taken for moving the file under the head i.e., the average latency and data rate. 

HDDs are available in two most common factors namely:

Ø  3.5 inch for desktop computers

Ø  2.5 inch for laptops

HDDs might be connected to the system by any of the following standard interface cables:

Ø  Serial ATA or SATA cable

Ø  USB cable

Ø  Serial attached SCSI or SAS cable

- In the year of 2012, flash memory emerged as a tough primary competitor for the hard disk drives. 

- These flash memories are some sort of solid state drives or SSDs. 

- However, the HDDs will still continue to dominate the secondary storage for its advantages such as price per unit of storage and recording capacity. 

- But there is a different scenario is the case of portable electronics.

- Here, the flash drives are considered to be more useful then rotating HDDs because here the durability and physical size of the drive has also to be considered more when compared to price and capacity.

HDD uses the magnetic recording technology where the data is recorded by magnetizing a thin film of material that is typically ferromagnetic on a disk. 

- The binary data bits are represented by the sequential change in the direction of the magnetization.

- An encoding scheme is used for encoding the user data. 

- An example of such encoding scheme run – length limited encoding. 

- It is these schemes that determine how the magnetic transitions would represent the data.

The latest HDD technologies are:

Ø  Shingled write

Ø  CPP/ MGR heads

Ø  Heat assisted magnetic recording

Ø  Bit – patterned recording

What is cache memory?

Cache memory is a certain memory aid for computers that speeds them up very well. 

- In cache memory, the storage of the data is transparent so as to make the processing of the future requests faster. 

- A cache might store in it the values that have already computed or duplicate of some values stored somewhere else in the memory. 

- Whenever some data is requested, it is first looked up in the cache memory. - If the data is found here, it is returned to the processor and this is called a ‘cache hit’. 

- In this case the time taken for accessing the data is reduced. 

- This access is thus faster than that of the main memory. 

- Another case is of cache miss when the required data is not found in the cache.

- Then again the data has to be fetched or computed from its original source or the storage location which is slow as obvious. 

- The overall performance of the system increases in proportion with the number of requests that can be served from the cache memory.

- In order to maintain the cost efficiency as well as efficiency in data usage, the size of the cache is kept relatively small as compared to the main memory. 

- However, the caches have proven themselves from time to time because of their ability to recognize the patterns of access in the applications having some locality of reference. 

- Temporal locality is exhibited by the references if the data that was previously requested is requested once again.

- These references apart from temporal locality also exhibit spatial locality if the storage location of the requested data is close to the data that was previously requested.

How is cache implemented?

- The cache is implemented as a memory block by the hardware and as a place of temporary storage. 

- Here, only that data is stored which is likely to be accessed again and again. 

- Caches are not only used by hard drives and CPUs but also by the web servers and browsers. 

- Pools of entries together make up the cache. 

- Each entry has a datum associated with and a copy of it is stored in the backing store. 

- Each entry is also tagged for the specification of the datum’s identity in the backing store.

- When a datum is required to be accessed by a cache client (it might be an operating system, CPU or web browser.) that it thinks might be available in the backing store, the cache is first checked. 

- If the desired entry is found, it is returned for the use. This is cache hit.

- Similarly, a web browser might look in its local cache available at the disk to see if it has the contents of a web page. 

- In this case the URL serves as the searching tag and the contents are the datum. 

- The rate of successful cache accesses is known as the hit rate of the cache.

- In case of a cache miss, the datum not cached is copied in to the cache so as to prevent future cache misses. 

- For making space for this datum, some already existing datum in the cache is removed. 

- Which datum is to be removed is determined by using the replacement algorithms. 

Explain the concepts of threads and processes in operating system?

Threads and processes are an important part of the operating systems that have features of multi–tasking and parallel programming. These come under the sole concept of ‘scheduling’. Let us try to understand these concepts with the help of an analogy.

- Consider the process to be a house and threads are its occupants. 

- Then, process is like a container having many attributes. 

- These attributes can be compared to that of a house such as number of rooms, floor space and so on. 

- Despite having so many attributes, this house is a passive thing which means it can’t perform anything on its own. 

- The active elements in this situation are the occupants of the home i.e., the threads. 

- The various attributes of the house are actually used by them. 

- Since you too live in a house you must have got an idea how it actually works and behaves. 

- You do whatever you like in the house if only you are there. 

- What if another person starts living with you? You just can’t do anything you want to do. 

- You cannot use the washroom without making sure that the other person is not there. 

- This can be related to multi – threading. 

- Just as a part of estate is occupied by the house, an amount of memory is occupied by the process. 

- Just as the occupants are allowed to freely access anything in the house, similarly the occupied memory is utilized by the threads that are a part of that process i.e., the access to memory is common. 

- If one process allocates some memory, it can be accessed by all other threads also. 

- If such a thing is happening, it has to be made sure that from all the threads, the access to the memory is synchronized. 

- If it cannot be synchronized, then it becomes clear that the memory has been allocated specifically to a thread. 

- But in actual, things are a lot more complicated because at some point of time everything has to be shared. 

- If one thread wants to use some resource that is already under use by some other thread, than that thread has to follow the concept of mutual exclusion. 

- An object known as the mutex is used by the thread for achieving exclusive access to that resource. 

- Mutex can be compared to a door lock. 

- Once a thread locks this, no other thread can use that resource until the mutex is again unlocked by that thread. 

- Mutex is one resource that a thread uses. 

- Now, suppose there are many threads waiting to use the resource when mutex is unlocked, the question that arises now is that who will be next one to use the resource. 

- This problem can be solved by either deciding on the basis of length of wait or on basis of priority. 

- Suppose there is a location that can be accessed by more than one threads simultaneously.

- You want to have only a limited number of threads using that memory location at any given point of time. 

- This problem cannot be solved by mutex but with another resource called semaphore. 

- Semaphore with a count of 1 is the resource that can only be used by one thread at a time. 

- In semaphore of greater count more threads can access it simultaneously.  

- It just depends up on how you characterize or set the lock.