need help with these questions (10 points) Suppose that you use the following encryption scheme each bit in the key R (a sequence of bits) is XORed with its corresponding bit in the plaintext M in order to get the ciphertext This simple scheme can be written as C M XOR R You want to use this scheme to encrypt your messages, where the language used for the messages has only two words represented as binary A 111 and B 000 For example, a message M could be 000111111000 but it can never be 010101 You have two messages, M1 and M2 You generated two keys R1 and R2 Unfortunately, R1 R2 You apply the encryption scheme mentioned above and get two ciphertexts, C1 and C2 C1 011101101001000111001 C2 011010010110000111110 Please identify a pair of plaintexts, M1 and M2, which yield C1 and C2 (5 points) And justify your solution (5 points) (18 points) Considering the following assignment of clearance classification levels for both subjects and objects Clearance Classification Level Subject Object High Administor System Configuration Medium Regular User User Configuration Low Guest Temporal File Fill out all cells for the access control matrix if a system uses Biba Model If the subject has read access to the object, you can put r in that cell If the subject has write access to the object, you can put w in that cell For instance, if A can read and write the object B, you can put r,w into the cell corresponding to (A, B) (9 Points 1 point for each cell) System Configuration User Configuration Temporal File Administor Regular User Guest Fill out all cells for the access control matrix if the system uses Low Water Mark policy after the administrator reads the Temporal File (9 Points 1 point for each cell) System Configuration User Configuration Temporal File Administor Regular User Guest (10 points) Modern operating systems have incorporated a bit non executable to label whether the content in a memory page (e g , a memory block) can be executed If stack frames are organized into these memory pages and labeled as non executable Will this stop the shellcode injected to the stack (e g , the buffer allocated in the stack) from be executed Please justify (10 points for undergraduates 5 points for graduates) Will this eradicate the possibility that an attacker executes unwanted code in the target system (undergraduates do not need to answer this question 5 points for graduates) Please justify (hint read attacks mentioned in this paper Anomaly Detection Using Call Stack Information )

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need help with these questions (10 points) Suppose that you use the following encryption scheme: each bit in the key R (a sequence of bits)

need help with these questions

(10 points) Suppose that you use the following encryption scheme: each bit in the key R (a sequence of bits) is XORed with its corresponding bit in the plaintext M in order to get the ciphertext. This simple scheme can be written as C=M XOR R. You want to use this scheme to encrypt your messages, where the language used for the messages has only two words represented as binary: A=111 and B=000. For example, a message M could be 000111111000 but it can never be 010101.

You have two messages, M1 and M2. You generated two keys R1 and R2. Unfortunately, R1=R2. You apply the encryption scheme mentioned above and get two ciphertexts, C1 and C2.

C1 = 011101101001000111001

C2 = 011010010110000111110

Please identify a pair of plaintexts, M1 and M2, which yield C1 and C2. (5 points) And justify your solution. (5 points)

(18 points) Considering the following assignment of clearance/classification levels for both subjects and objects.

Clearance/Classification Level	Subject	Object
High	Administor	System Configuration
Medium	Regular User	User Configuration
Low	Guest	Temporal File

Fill out all cells for the access control matrix if a system uses Biba Model. If the subject has read access to the object, you can put r in that cell. If the subject has write access to the object, you can put w in that cell. For instance, if A can read and write the object B, you can put r,w into the cell corresponding to (A, B). (9 Points 1 point for each cell)

	System Configuration	User Configuration	Temporal File
Administor
Regular User
Guest

Fill out all cells for the access control matrix if the system uses Low-Water Mark policy after the administrator reads the Temporal File. (9 Points 1 point for each cell)

	System Configuration	User Configuration	Temporal File
Administor
Regular User
Guest

(10 points) Modern operating systems have incorporated a bit non_executable to label whether the content in a memory page (e.g., a memory block) can be executed. If stack frames are organized into these memory pages and labeled as non_executable.
1. Will this stop the shellcode injected to the stack (e.g., the buffer allocated in the stack) from be executed? Please justify. (10 points for undergraduates; 5 points for graduates)
2. Will this eradicate the possibility that an attacker executes unwanted code in the target system? (undergraduates do not need to answer this question. 5 points for graduates) Please justify. (hint: read attacks mentioned in this paper Anomaly Detection Using Call Stack Information )