Database and Security

Question 1

How does a DBMS provide security for database users?

Answer 1

A DBMS provides security by assigning each database user an account with a unique username and password. These credentials are used to identify a user and control their access to the database.

Question 2

What is the role of usernames and passwords in DBMS security?

Answer 2

Usernames and passwords are used as credentials to authenticate and verify the identity of a user. These credentials are essential for controlling access to the database and ensuring that only authorized users can interact with the data.

Question 3

What actions does a DBMS verify when a user attempts to interact with the database?

Answer 3

When a user tries to interact with the database, the DBMS verifies the following actions:

Retrieve data
Modify data
Modify the database structure

Question 4

How does the DBMS use passwords in the security process?

Answer 4

The DBMS verifies passwords during the authentication process. When a user attempts to access the database, the provided password is checked against the stored password associated with the user’s account. If the passwords match, the user is authenticated, and their permissions are checked.

Question 5

Why is controlling access to information important in a DBMS?

Answer 5

Controlling access to information is crucial in a DBMS to ensure that only authorized users can view, modify, or alter the database. This helps in maintaining the confidentiality, integrity, and security of the data, preventing unauthorized access or tampering.

Question 6

In SQL, what are the common privileges used to control access to tables and other database objects?

Answer 6

The common privileges used in SQL to control access to tables and other database objects include:

SELECT privilege
INSERT privilege
UPDATE privilege
DELETE privilege

Question 7

Who has all privileges on all objects in a database, and how can these privileges be granted to others?

Answer 7

The owner (creator) of a database has all privileges on all objects in the database. The owner can grant these privileges to others.

Question 8

What privileges does the owner (creator) of an object have, and how can these privileges be passed on to others?

Answer 8

The owner (creator) of an object has all privileges on that object. The owner can pass these privileges on to others.

Question 9

How are privileges granted in SQL, and what are the components of the GRANT statement?

Answer 9

Privileges are granted in SQL using the GRANT statement. The components of the GRANT statement include:

<privileges>: A list of privileges such as SELECT, INSERT, UPDATE, DELETE, or ALL.
<object>: The name of a table or view.
<users>: A list of user names or PUBLIC.
[WITH GRANT OPTION]: An optional clause that means users can pass their granted privileges on to others.
</users></object></privileges>

Question 10

What is the significance of the WITH GRANT OPTION in the GRANT statement?

Answer 10

The WITH GRANT OPTION in the GRANT statement means that the users receiving the privileges can pass those privileges on to others. It allows for cascading the delegation of privileges in the security model.

Question 11

How can you remove a privilege that you have granted to another user in SQL?

Answer 11

To remove a privilege that you have granted, you use the REVOKE statement in SQL. The syntax is as follows:

REVOKE <privileges>
ON <object>
FROM <users>;</users></object></privileges>

Question 12

What happens if a user has the same privilege from multiple users, and one user revokes the privilege?

Answer 12

If a user has the same privilege from multiple users, and one user revokes the privilege, the user will still retain the privilege from the other users. The revocation only affects the privileges granted by the specific user issuing the REVOKE statement.

Question 13

In the context of privilege revocation, what happens to privileges that are dependent on the revoked one?

Answer 13

When a privilege is revoked, all privileges that are dependent on the revoked one are also revoked. This ensures consistency in the security model.

Question 14

Provide an example scenario of granting and revoking privileges among users in SQL.

Answer 14

Example Scenario:

‘Admin’ grants ALL privileges to ‘King’ and SELECT privilege to ‘Princess’ with the grant option.
‘King’ grants ALL privileges to ‘Farmer’.
‘Princess’ grants SELECT privilege to ‘Farmer’.
If ‘Admin’ revokes privileges from ‘King’, both ‘King’ and ‘Farmer’ lose their privileges. ‘Princess’ retains her SELECT privilege.

Question 15

What does the “WITH GRANT OPTION” mean in the context of granting privileges?

Answer 15

The “WITH GRANT OPTION” in the GRANT statement means that the users receiving the privileges can pass those privileges on to others. It allows for the delegation of privileges in the security model.

Question 16

How do privileges work at the level of tables in a database?

Answer 16

Privileges in a database work at the level of tables, allowing control over access to entire tables. These privileges can include restrictions on operations such as SELECT, INSERT, UPDATE, and DELETE.

Question 17

Can you restrict access by column using privileges in a database?

Answer 17

Yes, you can restrict access by column using privileges in a database. This means you can control which columns a user has permission to access or modify.

Question 18

What limitation exists when using privileges alone in restricting access?

Answer 18

While privileges can restrict access by column, they cannot restrict access by row. This limitation is addressed by using views in conjunction with privileges.

Question 19

How do views, along with privileges, contribute to customized access in a database?

Answer 19

Views provide a way to create “derived” tables based on SELECT statements, and privileges can be granted or revoked on these views. This combination allows for customized access by presenting users with specific subsets of data through views.

Question 20

What is a view in the context of a database?

Answer 20

In the context of a database, a view is the result of a SELECT statement treated like a table. It provides a way to create a virtual table that represents a subset of data from one or more tables in the database.

Question 21

How are views and privileges used together to control access in a database?

Answer 21

Views and privileges are used together by creating views that contain the necessary information only, and then granting or revoking privileges on those views rather than directly on the underlying tables. This allows for a more fine-grained control of access.

Question 22

In the RSA cryptosystem, what is the primary goal when encrypting a message for secure communication?

Answer 22

The primary goal when encrypting a message in the RSA cryptosystem is to ensure that it is very difficult for a potential interceptor (hacker) to infer the original message from the encrypted ciphertext.

Question 23

What form is the message (m) in when using the RSA cryptosystem, and how is it regarded for encryption?

Answer 23

In the RSA cryptosystem, the message (m) is regarded in its binary form, meaning it is treated as a sequence of 0’s and 1’s. It is regarded as a (potentially very large) integer, allowing for encryption and decryption operations.

Question 24

Why is the preparation step in the RSA cryptosystem carried out only once?

Answer 24

The preparation step in the RSA cryptosystem involves generating two keys: a public key and a private key. These keys are used for encryption and decryption, respectively. Once generated, the keys can be used for secure communication indefinitely, and the preparation step need not be repeated for each message.

Question 25

What are the three main steps in the RSA cryptosystem, and what is the purpose of each step?

Answer 25

The three main steps in the RSA cryptosystem are:

Preparation: Alice prepares two keys - a public key and a private key. This step is carried out only once and the keys are used for all subsequent communications.
Encryption: Bob encrypts his message (m) into a ciphertext (C) using Alice’s public key. This ensures that the message is secure during transmission over a public network.
Decryption: Alice converts the received ciphertext (C) back to the original message (m) using her private key. This step allows only the intended recipient to retrieve the original message.

Question 26

What makes the RSA cryptosystem secure for communication over a public network?

Answer 26

The RSA cryptosystem is secure for communication over a public network because it is based on the mathematical difficulty of factoring the product of two large prime numbers. The encryption and decryption processes involve the use of public and private keys, and the security relies on the impracticality of factoring the large composite number used in the algorithm.

Question 27

In the RSA cryptosystem, what are the key steps in Alice’s preparation phase?

Answer 27

The key steps in Alice’s preparation phase in the RSA cryptosystem are as follows:

Choose Primes: Randomly choose two large prime numbers, p and q.
Compute n: Calculate n as the product of p and q (n = p * q).
Compute φ (Phi): Calculate φ (phi) as (p - 1)(q - 1).
Choose e: Select a number e from the range [1, φ - 1] that is co-prime to φ (i.e., the greatest common divisor of e and φ is 1).
Compute d: Calculate a number d from the range [1, φ - 1] such that (e * d) mod φ = 1.
Public and Private Keys: Announce the pair (e, n) as the public key to the world. Keep the pair (d, n) as the private key secret to herself.

Question 28

Why is it important for e to be co-prime to φ in the RSA cryptosystem?

Answer 28

It is important for e to be co-prime to φ in the RSA cryptosystem because the security of the system relies on the difficulty of factoring the product of two large prime numbers (n = p * q). The co-primality ensures that there is no common factor between e and φ, making it computationally challenging for an attacker to deduce the private key d.

Question 29

What is the significance of the pair (e, n) in the RSA cryptosystem, and why is it announced publicly?

Answer 29

The pair (e, n) is the public key in the RSA cryptosystem. It is announced publicly to allow others, such as Bob, to encrypt messages intended for Alice. The public key (e, n) is used for encryption, and it is not sensitive information. Anyone can use the public key to encrypt a message, but only Alice, who possesses the corresponding private key, can decrypt it.

Question 30

Why does Alice keep the pair (d, n) as the private key secret?

Answer 30

The pair (d, n) is the private key in the RSA cryptosystem. Keeping it secret is essential to maintain the security of the system. The private key is used for decryption, allowing only Alice to recover the original message from the encrypted ciphertext. Revealing the private key would compromise the confidentiality of the communication.

Question 31

What mathematical relationship should hold between e and d in the RSA cryptosystem?

Answer 31

In the RSA cryptosystem, the mathematical relationship between e and d is that (e * d) mod φ = 1. This relationship ensures the correctness of the encryption and decryption processes and is a fundamental property of the RSA algorithm.

Question 32

In the RSA cryptosystem, what is the formula for encrypting a message (m) into ciphertext (C)?

Answer 32

The formula for encrypting a message (m) into ciphertext (C) in the RSA cryptosystem is:
C≡m^e (mod n)

Question 33

What are the components involved in the encryption formula
C ≡ m^e (mod n)?

Answer 33

C: The ciphertext.

m: The original message.

e: The public exponent from Alice’s public key.

n: The product of the two large prime numbers from Alice’s public key.

Question 34

Why is the use of modular arithmetic (mod n) important in the encryption formula?

Answer 34

The use of modular arithmetic (mod n) is important in the encryption formula to ensure that the result remains within a certain range. It helps prevent arithmetic overflow and keeps the ciphertext within manageable bounds. Additionally, modular arithmetic supports the mathematical properties necessary for the security of the RSA cryptosystem.

Question 35

After Bob encrypts a message using Alice’s public key, what does he send to Alice?

Answer 35

After Bob encrypts a message using Alice’s public key, he sends the resulting ciphertext (C) to Alice. The ciphertext is the encrypted form of the original message, and only Alice, with her private key, can decrypt and recover the original message.

Question 36

In the RSA cryptosystem, what is the formula for decrypting ciphertext (C) to recover the original message (m)?

Answer 36

The formula for decrypting ciphertext (C) to recover the original message (m) in the RSA cryptosystem is:
m≡C^d (mod n)

Question 37

What are the components involved in the decryption formula

m≡C^d (mod n)?

Answer 37

m: The original message to be recovered.

C: The ciphertext received from the sender.

d: The private exponent from Alice’s private key.

n: The product of the two large prime numbers from Alice’s private key.

Question 38

Why is the use of modular arithmetic (mod n) important in the decryption formula?

Answer 38

Similar to encryption, the use of modular arithmetic (mod n) is important in the decryption formula to ensure that the result remains within a certain range. It helps prevent arithmetic overflow and keeps the recovered message within manageable bounds. Additionally, modular arithmetic supports the mathematical properties necessary for the security of the RSA cryptosystem.

Question 39

After decrypting a ciphertext using her private key, what does Alice recover?

Answer 39

After decrypting a ciphertext using her private key, Alice recovers the original message (m). The decrypted message is the result of applying the decryption formula
m≡C^d (mod n) to the received ciphertext.

Question 40

In the RSA cryptosystem, what is the primary weakness that an attacker exploits to break the system?

Answer 40

The primary weakness in the RSA cryptosystem that an attacker exploits is the difficulty of factoring the product of two large prime numbers (n = p * q). If an attacker can factorize n back into its prime factors (p and q), they can reveal the entire preparation carried out by Alice and obtain the private key components.

Question 41

What is the significance of factorizing n into p and q in breaking RSA?

Answer 41

Factorizing n into p and q is significant in breaking RSA because it reveals the prime factors used in the key generation process. Once the prime factors are known, an attacker can compute φ (phi) and, subsequently, compute the private key exponent (d) from the public key exponent (e) and φ. With the private key, the attacker can decrypt ciphertexts and recover the original messages.

Question 42

Why is obtaining φ crucial in breaking RSA?

Answer 42

Obtaining φ (phi) is crucial in breaking RSA because it is used in the computation of the private key exponent (d). The relationship between e, d, and φ is a fundamental property of the RSA algorithm. If an attacker can obtain φ, they can calculate the private key exponent and, consequently, decrypt ciphertexts using the private key.

Question 43

What does the attacker need to compute once they have factored n, obtained φ, and revealed the entire preparation carried out by Alice?

Answer 43

Once the attacker has factored n, obtained φ, and revealed the entire preparation carried out by Alice, the attacker needs to compute the private key exponent (d) from the public key exponent (e) and φ. With the computed private key, the attacker can then use it to decrypt ciphertexts (C) and recover the original messages (m).

Question 44

What is the main countermeasure to prevent RSA from being broken?

Answer 44

The main countermeasure to prevent RSA from being broken is to use sufficiently large prime numbers for key generation. As the security of RSA relies on the difficulty of factoring the product of two large primes, using larger prime numbers increases the computational effort required by an attacker to factorize n and break the system.