(a)Access control matrix- It is a security model used for protection of computer system which defines the right of each object in the system. It is an array to keep the data secure like date, time, location, identity and previous records and information is safeguarded from everyone except the one who need to low. This approach is used in practise as it provides permission of concrete access. Access to any type of information is regulated by access control matrix and limits electronic access to a network, computer, and digital file by an unauthorised user.
(b) Access control list (ACL) store column of matrix with the resource and widely used in groups where in capabilities are used to hold a ticket to use each of the resource. Access control list is associated with each object in the system and provide authentication to object in the list. Capabilities are random bit of sequence which is managed by operating System which can be passed from one process to another. ACL and capability is related to Access control matrix as it indicates who is allowed to perform, what function can be done,who can read, write or manipulate the information.
Advantages and Disadvantages- ACL has set of accessible objects which are not bounded and is based on the users, but in case of ACL there are chances of worms, virus and stack overflow attacks. In case of Capability every process has a specific set of access rights also deleting a operator from the list to access the resource can’t be done by capability. In short it provides varying levels of security and prevention from thefts.
(c) Windows access control system out performs todays standard offerings in terms of expandability, flexibility and performance. Windows access control system is based on latest .net software platform. Process- It segregates all the information of its security token STS, STS access an incorruptible gateway within an authentication system. Future, security token is a digital key which authorize a person access to security gate.
Role of Security Reference Monitor (SRM)- It defines set of access control policies on a system to ensure access by authenticated user. It provides sequence to work with access control.
Role of Access Control Lists (ACLs) and Access Control Entries (ACEs) – ACL is sued to determine which object has what security and defines what functions can be done future who can read, write or manipulate the information. ACEs are entries in access control list which contains the access rights information related to each user in the system.
Role of Security Identi?ers (SIDs)- Each user is linked to a unique Id which is used to authorizing the identity of a user uniquely.
(d) Access control model for information is used for protecting resource and also control the permission of the file. It focuses on security issues using security labels that denote security classes. Security label is a gate for the sensitivity of data, if the user don’t clear the gate it cannot access the information of the system (Choi & Kim, 2014).
(a) Malware is also known as ‘malicious software’. It often gets installed in our computers without our prior knowledge and decreases the performance of the system, redirects to other pages automatically and so on. Malware do things like stealing personal information like credit cards numbers or password delete some information; attack other network or sending spam mails. Some examples are viruses, worms, spyware, adware and Trojans. Viruses are software that are created to damage or harm the system where in Worms infects computer and make it very slow.
(b) Real life example of worm and viruses: MyDoom it is spreading via E-mail, it is junk in a amil file it progates in other system and injects the other system also. Sasser is a worm which spreads and inject the system by scanning the IP address and downloading the virus I the personal systems.
(d) (i) Buffer overflow is when data overwrites the memory locations as there is no space available in the memory. Attacker uses this for purposely for crashing the target system as buffer overflow leads to changing the layout of a program by replacing it with some malicious code. Buffer overflow is one of the weaknesses of security as it enables hacker to modify the internal variables. It leads to vulnerabilities as the additional data may contain malicious code which may result in unofficial access to the organization. Attacker tries to exploit the buffer overflow to change the architecture and operating system.
(ii) To reduce the risk of buffer overflow process known as fuzzing is used to check if the system accepts additional data or not. Stack Guard is a complier used to prevent and stop stack buffer overflow. If the attacker tries to overwrite the buffer section, it won’t be possible. Other than that there are some tools used to identify buffer overflow. Functions like strncpy() is used for prevention as it examine and eliminates bugs from the software. As removing bugs from a program is not feasible but using these functions it is possible to some extent.
(e) Type safety is used to prevent type errors that usually occur due to different data types. It ensures that the program is well defined and behaves properly. C, C++ is not at type safe language wherein the platform of Java, Python and Ruby is type safe. Type safety ensures that operations of an object are always compatible and the program will not go wrong at the run time. It is useful as it shows the strength by enforcing variants in the program, and enforces abstract types which characterize the modules and keep it hidden from clients.Type safety enforces garbage collection which avoids temporal violations of memory but uses more memory.
(a) An address is used to refer to a location in computer memory
(i) Fundamental difference between virtual and physical address is that virtual address is generated during the execution of a program by CPU. It is not possible to access the physical address directly by the user where logical address can be used to access the physical address. Physical address deals with load time address binding wherein virtual address deals with compile time address binding.
(ii) Using Virtual management system is very important as it helps in clearing the shared memory space. Also if the application is not in use, freeing it in turn increase memory isolation by using the technique of paging. (a) It eliminates the concept of external fragmentation as pages are mapped automatically. (b) Also allocating the memory is cheap and efficient and is part of memory management as it creates virtual memory space for the system.
(b) (i) Privileges level are used by processor to grant different access rights to the user. As each user cannot be granted with all the permission, thus using these privileges level by the processor limited access is provided.
(ii) There are three privileges level, zero level allow the user to access all the commands and information, then user level is used to provide limited access to user by granting read only permission, then last is privileged level that grants complete control over the system.
(iii) The new Intel processor privilege level has four levels now, in which an zero level is assigned to operating system of kernel and ring 3 is used by users. If a program is designed to operate in zero level it cannot be used outside the assigned privilege level.
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(c)(i) DMA is an attack which violets computer security as an attacker can penetrate in the system. If a device is using DMA an unimpeded access to some address space would bypass security measures by installing malwares in the system, access the encryption keys violating confidentiality. Other than that a proper synchronization mechanism is needed in the device to avoid accessing non updated information. It sometimes leads to cache coherency problem if the data stored in RAM is not updates with the correct data in cache. |
(ii) Intel Trusted Execution Technology (Intel TXT) has primarily goals of providing authenticity to operating system and creates a secure environment. Intel processor partitions the protected data, the protected partition cannot be modified from other processor thus protect it from DMA. Similarly, Intel chipset provides isolation to data sets to ensure the protection of data also various Authenticated Code modules generates secure cryptography keys and provides trusted environment at runtime.
(ii) Buffer overflow is caused due to malicious attacker who sends wrong input in the program and attempts to store in the buffer which is not large enough. Buffer flow is caused as some languages do not have any built in protection against overwriting data in the memory.
(iii) Buffer overflow can be reduced by using a process known as fuzzing, which checks that the system is not accepting additional data. Stack Guard complier can be used to stop buffer overflow, as when the attacker tries to overwrite the buffer section, it is not possible. Other functions like strncpy() is used to avoid and eliminate the bugs from the software.
(b) (i) If an incompatible operand is passed to a function, which cannot be handled by the data type causes type error. It also causes vulnerabilities in software; there are two type of errors type1 and type2. Type1 inserts incorrect value and type2 create virtual existence of the thing that is not present. It doesn’t resemble the usual data types used like strings, arrays, objects and Java script function. Type Error is usual caused due to using wrong data types or operations.
(ii) Type safety uses complier to automatically check the type at the time of compiling and throws an error if the assigned data type to the variable is not correct. It help in providing secure environment as it do not allow to access any private memory location or member whose permission is not granted to be accessed. It makes sure that objects are isolated from one another. Thus type safety creates a safe environment and avoids chances of attack.
(c) (i)Arc injection attack inject a jump to redirect the execution of a program t some other code area in the memory. It is also known as return to libc attack where library as lot of predefined codes that re useful for the attacker which provides type definitions, string handling mechanism, memory allocation and other operating system services. Because of availability of the large number of functions libc’s codes are used instead of using code injection technique.
(ii) There are various compliers which are used to identify stack problems. Like using -fstack function is useful as it provides solution for the worst condition by using canary space fundamental. Canary space is used at the end of the stack so that data can be written after it has been modified. Another method is using CPU watchpoints, it a way to look at the canary space condition for accessing it. This software implementation is used to check the availability of canary space automatically after predefined intervals so that problem of buffer overflow doesn’t occur.
Answer to question
(i) If the password is communicated through an insecure root or stored in the insecure network may lead to malicious user accessing the data. Any hostile user may enter the system and track all the information which destroys the confidentiality of the information (Du, 2011).
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(ii) The risk of password can be reduced by using the password on the secure environment. When the password is shared over network it is encrypted so that no third party user can track it. |
(b) Biometric system is used in security purpose as it works by mapping the pattern of human with the use of advanced technology. The architecture of biometric basically connects software and hardware components. Finger print is one of the biometric system, which include various components.
Sensor- It captures the digital image of finger which is future processed and stored in the database for identifying the correct user. Verifying the correct user helps in attaining a good security.
Processor- The stored mage in the database is minutely observed and processed as the security relies in matching the input minutely. The scanned input is future processed like performing segmentation, normalization and estimating the frequency of image which is future applied to enhance the quality of image for extraction.
Extractor- Finding the similarity and finding the correct match, is done using the concept of crossing number.
Identification- finally identifying the correct user by matching the finger prints and identifying it helps people to save time. Only the correct user is identified and granted the access to information.
Answer to question no. 4
(ii) Access mask is used to describe access rights which specify that the request is granted to an object or it can access the object or not. Access mask make sure that access right assigned are used correctly.
Subject is basically defined as person or agent who wants to access the information, Role is a job function that defines the authority level of access, or it is organizational function with a clear definition of inherent responsibility and authority.
Permission is mode of accessing the file that is read, write or execute. Permission is assigned to role, and by using this permission it is determined that the user is allowed to access the data in the system or not. User-role permission makes the work simple to perform user assignment.
(ii) Hierarchal RBAC provides additional support of inheritance between roles like an inheritance relation among roles. Inheritance can be described in terms of permissions that is r1 “inherits” role r2 if all privileges of r2 are also privileges of r1. It composes the role from multiple subordinate roles and defines the relations and roles that are intended to be represented. Then it provide uniform treatment of user or role assignment, which can be included in the role hierarchy, using the same relation to denote the user assignment to roles, as well as permission inheritance from a role to its assigned users.
Answer to question no. 3
(i) Buffer overflow is a program where writing data in buffer exceeds the buffer boundary which in turn overwrites the exciting data with the new one as buffer is not able to handle the extra data.
(ii) Buffer overflow can be caused like in s7case of stack when the size is predefined and if additional data is entered in the stack will lead to overflow. Similarly, if the size of a file is fixed it cannot store additional data in it, if data is entered are than the defined capacity will lead to buffer overflow.
(iii) Risk of buffer overflow can be avoided by using safe libraries as in C, C++ buffer overflow is very common thus high degree of correctness can be maintained by using standard library functions. These standard library functions automatically take cares of buffer management and reducing the chances of buffer overflow. Also by using pointer protection as it prevents attacker to encode/decode pointers and it automatically XORs pointers and also checks the buffer space before sending it to buffer memory.
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(b) (i) Type error occurs when an operand is passed to a function which is incompatible to handle that data type. It cause software vulnerabilities as type I is it inserts incorrect value of true and type II create virtual hypothesis of the thing which is not there and falsely interprets the presence or absence of something. It doesn’t recognize the usual data types like arrays, numbers, objects, strings and the JavaScript function. Thus using wrong data types or operations cause Type Error. |
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(ii) Type safety refers that complier automatically validates the type while compiling and instantly throws an error if wrong type is assigned to the variable. It provides a secure environment as it doesn’t access of any private members or memory location that it not permitted to be accessed. It also ensures that objects are isolated from each other. Therefore safe environment is created and avoid malicious corruption or undefined behaviour. For secure system it also provides the requirement for explicit type conversion for a language so that it doesn’t leads unexpected or unintuitive behaviour. |
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(c) |
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(i) Arc injection is also known a Return-to-libc, libs is a program having various useful functions like C library standards, type definitions, memory allocation and various operating system services. It redirects the execution flow to other code of the memory. It is caused because due to inserting of large number of data which causes difficulty of executing code on stack thus causes memory attack. It provides the solution if buffer is not big enough for the code. |
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(ii) There are some compilers which is used to identify stacks problems. First is using –fstack it creates the solution for worst case scenario by creating canary space at the end of each task so that even if the data is modified it can be written. Second method is using CPU watchpoints which includes a way to watch the canary space for writing access. Thus this software implementation is used to check the canary space at a predefined interval so that buffer overflow doesn’t occur. |
Answer to question no. 4
(a)
(i) The key difference between logical and physical difference is that it is not possible to access the physical address directly by the user where logical address can be used to access the physical address. Physical address deals with load time address binding wherein virtual address deals with compile time address binding.
(ii) Virtual memory allows more than one applications to run on the system, it is used by operating system to provide hardware support, allows running more applications at once and allows running larger applications with less real RAM and it is not necessary to buy more memory. It has the ability to load and execute a program in less memory space even if it requires a larger amount of memory.
(b)
(i) These privilege levels are also known as protection rings, in the ring the innermost ring has highest priority which tends to protect data from faults by improving fault tolerance capacity and avoiding malicious and providing computer security. The level 0 is used by the kernel and level 3 is used by application programs. These levels ensure that data is protected to a certain extent and saves the software to avoid vulnerabilities (Gollmann & Snekkenes, 2017).
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(ii) In Unix system the supervisor owns all the privilege levels and provides security to the system. Different privileges level assigns the access rights accordingly. The least privileged level grant the access right to everyone, whereas the most privileged level in the system is granted to the one who control the entire system. |
(c)(i) Direct memory access is used for violating attacks and maintains computer security so that attack does not penetrate in the system. By using DMA an unauthorized access to address space is not possible but due to directly accessing memory space it installs malware in the system which in turn violates the confidentiality of data. Other than that a correct synchronization tool is needed in the device to evade accessing un-updated information. Sometimes using data stored in RAM it leads to cache coherency problem if the data is not updated with the correct data in cache.
(ii) Intel TXT stands for Intel Trusted Execution Technology have fundamental goals of providing authenticity to operating system and create a protected environment. It uses the concept of portioning the data, protected data is portioned and cannot be modified by other processor and it also protects data from direct access. Similarly, Intel chipset provides isolation to data sets to ensure the protection of data also various Authenticated Code modules generates secure cryptography keys and provides trusted environment at runtime.
Answer to question no. 5
Uid is a unique identifier to identify the system, su is used to promotes the status of super user. The /etc/shadow file contains encrypted passwords as well as ageing and information when the password will expire.
(ii) The password file is secure and it contains user information and provides rights that who can see the list of passwords and hashes. These password file is important for security purpose and it is installed in default. The right to permission to access these files are assigned. It helps in keeping track of each user on the system. It contains information like username, identity of user and also basic account information for each user is mentioned.
(iii) The salt is a string of two characters used to perturb the algorithm in many different ways. It encrypts the string constantly and returns the encrypted password value. Exhaustive searches of space are also possible by using parallel spacing. DES algorithm makes use of cryptography for password authentication. In this there is a problem of password allocation to other file which can be resolved by shadow file.
(iv) There are vulnerabilities in this approach as all the information is visible to user, so people can use the password and save it on back-up and can be misused as /etc/password keep actual password stored. The information is stored in readable form as it contains the password information which could be readable by unprivileged user which makes the system vulnerable to interception.
(v) Unix is stable and is flexible which is built to provide high security and permission features than before. It solves the problem of creating large monolithic programs by offering support of virtual memory. Where user can run number of programs at the same time and have rich collection of small utilities/commands to perform tasks.
(ii) Only the root or super user is allowed to change the permission of a directory or file. It can set the access permission of read, write or execute in the system.
Answer to question no. 1
(ii) Principals which can be used for development of secure software
By reducing the surface area- Every application added on the system adds some amount. To avoid the risk surface area should be less so that there is no vulnerabilities. Additionally controlling the access privilege to resources limits the chance of unauthorized attacks.
Fixing security issues correctly- It is important to fix the bugs so that it do not penetrate in the system and cause failure later on. Thus developing and fixing the issues without introducing regressions is essential.
(b) (i) Viruses are worms are malicious programs and cause damage to the system but there is a difference. Viruses get attached to the programs and spread from one system due to some human action to another leaving infections in the whole way wherein worms travel from other system to other without any human action. Worms travel via e-mail and viruses are hidden in word file. Worms spread faster than virus as it has the capability to replicate itself.
(ii) It is true that worms cause more severe threats as it has the capability of copying and travel across but it consumes too much of systems memory and also consumes high bandwidth just responding to web servers by making them slow and eventually stopping them to respond. Internet worms exploit the access rights and create the network unprotected.
(c)(i)Malware signature is a unique bit of strings which act as fingerprint to detect o identify the viruses. It basically scans the occurrence of malicious code in the system. Signatures are also used to detect the attacks by matching patterns and bit sequences in network traffic.
(ii) Techniques used to hide malware are using packers as it wraps the signature and decodes only at the time of runtime. These packers are used to hide signatures from malware. Crypters are used to encrypt the fingerprints to avoid the detection of signatures. Other technique is using polymorphic malware which automatically uses the packer and crypter technique to change the look of signature.
Answer to question no. 2
(ii) Threats can be prevented by using proper encryption techniques, avoiding spoofing and sniffing where third party hides their true identity and tries to access the data, using updated antiviruses. Encryption is the process to keep the text saves in chipper text form so that the text can be decrypted only by a valid user and this avoids the chances of leakage of data.
(iii) If the effect of threats has destroyed the entire system, and finically extra support is needed to remove the bug and bring the system back to the original condition, count measure technique is used in that case.
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(iv) Shortcomings of using numerical approach to risk management is that the analysis is not precise and is confusing sometimes. Numerical analysis is generally expensive and demand advanced tools for calculations. By using this approach it requires more amount of time with bigger expenditure. |
Difference between segmentation and paging is that in paging physical memory is divided into fixed size frames, when memory is needed available frames are allocated and are located anywhere in the memory whereas in segmentation memory is not divided systematically and these segments are placed in the available holes of memory. Also page is a fixed sized blocks whereas segment is a variable-sized block.
(ii) Difference between paging and segmentation on the basic of security is that paging allocates the memory anywhere in the memory with can be attacked by the third party user as attacker knows that it is fixed size block and tries to capture the pattern of memory.
(iii) Paging don’t support external fragmentation and the segments can grow without any reshuffling of pages. But it supports flexibility of sharing the information and process can run even if the pages are swapped. Segmentation is useful as it decrease the size of table and decreases the overhead of memory
(c) (i) Interrupt vector table is used to list the interrupt handlers. Interrupt vector is the memory location which in turn handlers interrupt and give priority to interrupts and saves the interrupts in the queue. So that even if more than one interrupt occurs it can be handled using Interrupt vector table.
(ii) In interrupt driven software the problems of security arises as the interrupt overload is very high and it usually causes the problem of stack overflow.
Answer to question no. 4
Sensor – It captures digital image which is processed and stored in the database which is future used for identification and verification. It helps in attaining advance method for security.
Image Processor- The image stored in database is processed minutely as the performance and security measures relies on the input scanned. Many processes are applied to image like image segmentation, normalization and estimation of frequency which are applied to boost the quality of image in terms of usability for minutia extraction.
Minutia Extractor- The concept of crossing number is used to match the similarities between two ridges and finding out if they are identical or not.
Identification- Finally, identifying and verifying the processes which help people to be clear and save time. Only the correct under is identified and granted the permission to access the data.
(i) Tokens are used to authorize access to a network, it is based on authentication which ensures that every request to server is convoyed to a signed token which in turn verifies the authenticity and then replies to the request. These tokens transfer one time password over the network or some unique identity which is confidential and cannot be disclosed. Each user in the system has user tokens that are generated so that users access the services without disclosing their actual credentials.
(ii) Previously applications used confirm the user identity through session cookies, but only token authentication uses tokens and lower the load of the network, user generates the token, using this token user connects to the server and request for the information on the server.
Answer to question no. 1
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(a) (i) Computer security refers to protection of information, network as well as computation power. It provides protection to the system from thefts and disruptions. It ensures that data is encrypted and cannot be accessed by unauthorized user. Computer security guarantees that to damage occurs to the hardware, software or services of computer. |
(ii) The three corresponding security notions of security described by Anderson in 1972 are
Other one is if the password file is modified by unauthorized user than the actual user will not be able to access the file. Denial of use is a major problem as actual user is not able to open is file even if it is authorised.
(b Reference monitor encapsulates the access method which supports certain security policies and before accessing the resources permission is asked. It satisfies the properties of completeness, isolation and verifiability. Reference validation is used to describe the set of requirements, and then validation is encompassed on the requirements of proper access policies. As well as trusted computing base is a collection of firmware’s that take care of the bugs and vulnerabilities occurring in the system.
Reference monitor provides aces to the user processors and gain access of objects from the operating system.
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(c) Software bug is an error or fault in the system which decreases the productivity, and cause the system to behave in different way. Vulnerability is defined as the capacity of that cause harmful effects on the system and cause security risk. Threats cause damage to the system. |
Answer to question no. 2
(i) Access control matrix- It is a safekeeping model which provides protection of computer system and also defines the right of every entity in the system. It uses an array to keep the data secure from everyone except the one who is authorized. This approach is used in to provide access permission to users. Access to any type of data is controlled by access control matrix and bounds the unauthorized access to a network, computer and digital file by an unauthorised user.
(ii) Access control list (ACL) is used to store the data regarding the resources in the column of matrix whereas the capabilities are used to hold a permit to use each of the resource. Access control list is related with every object in the system which provides authentication to all the object in the list. Capabilities are casual arrangement of bits which is managed by operating system and is passed from one process to other. Both the terms are related to Access control matrix which indicates what function can be done, who can perform the functions like who are allowed to read, write or manipulate the information.
(c) Unix access control system.
Uid is a unique identifier to identify the user of the system; gid is used to provide identity to group of users; su is used to stimulate the status of root user. The /etc/shadow file contains encoded passwords as well as the information about when the password session will expire.
(ii) The working mechanism of access control varies in various levels. First level is user level then the middle level which expresses security policy, adds more protection so that application can be written and provides proper access control to users. Memory address is assigned to each process and permission is granted like for read ‘r’ is used; for giving the permission to modify the file ‘w’ is used and for execution of file ‘x’ is used. (-) is used for granting no permission to the user. Several users in the system are: root user, system user and group user. Super user or root user have unlimited access and holds the ability to make any kind of changes in the system. On the other hand system user cannot make any changes and access the file according to the permission granted.
Answer to question no. 3
(ii) By using the concept of Virtual management is efficient for the system as it helps in clears the shared memory space and makes it available for other task. Also if the program is not in use, freeing the space at that particular time increases memory isolation and this is done by paging. (a) It also eliminates the theory of external fragmentation as pages are mapped automatically. (b) Method used for allocating the memory is cheap and very efficient and it also creates virtual space in the system.
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(b) (i) The primary objective of memory management is to provide a detailed description of hardware and provide relocation that is the ability to move the process in the memory space without having the effect on its execution and also allows sharing of process to access the portion of main memory without compromising the protection. (ii) The updated privilege level of Intel has aim of providing authenticity to operating system and creates a secure network. The data is partitions into many portions; the important data is kept in protected partition which cannot be modified from any the processor. It has 4 levels, the zeroth level is assigned to operating system and the rest levels are used by users. The privileges of each level are bounded to its own level. |
(i) Memory management is used as it dynamically allocates the memory portions whenever the programs need it. Also when the memory is not needed by the program it frees it automatically making it available for other programs.
(ii) Allocation of memory occurs by partition pool method in which dynamically memory blocks are allocated to the program whenever program needs extra memory. Similarly, like garbage collector is used to free the memory space, memory management automatically reallocated the block of memory space which is not in use.
References
Borders, K. R. (2015). U.S. Patent No. 9,055,093. Washington, DC: U.S. Patent and Trademark Office.
Choi, C., Choi, J., & Kim, P. (2014). Ontology-based access control model for security policy reasoning in cloud computing. The Journal of Supercomputing, 67(3), 711-722.
Du, W. (2011). SEED: hands-on lab exercises for computer security education. IEEE Security & Privacy, 9(5), 70-73.
Gollmann, D., & Snekkenes, E. (Eds.). (2017). Computer Security–ESORICS 2017: 22nd European Symposium on Research in Computer Security, Oslo, Norway, September 11-15, 2017, Proceedings (Vol. 10492). Springer.
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