Cryptography MCQ Quiz in मल्याळम - Objective Question with Answer for Cryptography - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

The correct answer is Decryption

Key Points

• Hashing is a one-way process that creates a unique fingerprint for your data. It cannot be used to recover the original data (plain text).
• Substitution is a technique used in encryption where characters are replaced with others. It's a building block, not the decryption process itself.
• Encryption scrambles the plain text into ciphertext, making it unreadable. It's the opposite of decryption.
• Decryption uses the encryption key to reverse the scrambling process, converting ciphertext back to the original plain text.

So, the correct answer is option 4 Decryption. 

The correct answer is Confidentiality

 Key PointsConfidentiality:

• A digital signature does not inherently provide confidentiality. This means that if someone intercepts the message, they can read its content.
• Confidentiality must be ensured by other means, such as encryption. Encryption scrambles the content of a message so that it can be understood only by someone who has the corresponding decryption key.
• This keep the contents hidden from anyone who might intercept the message during transmission.
• In other words, digital signature alone cannot prevent unwanted third parties from reading the message if it is intercepted; it only ensures that the receiver will know if the message was tampered with during transmission.

Additional InformationA digital signature provides three functions:

• Authentication: It verifies the sender's identity. The receiver can be sure that the message was indeed sent by the claimed sender, as it's based on the sender's private key, which is not publicly accessible.
• Non-Repudiation: It ensures that the sender cannot deny having sent the message. Once signed with a digital signature, a message can always be proven to have been signed by that unique private key.
• Integrity: It verifies that the message content has not been altered in transit. Any modification to the message would alter the signature and, therefore, be detected at the receiving end.

The Data Encryption Standard is a symmetric-key algorithm for the encryption of digital data.

Data encryption standard (DES) is a block cipher that encrypts data in blocks of size 64 bits each. That is 64 bits of plain text goes input to the DES which produces 64 bit of cipher text. Key length is 56 bits.

DES is insecure due to the relatively short 56-bit key size.

Important Points

Broad level steps of DES are:

• In first step, 64 – bit plain text block is handed over to initial permutation.
• Next , initial permutation (IP) produces two halves of permuted block, say left plain text and right plain text
• Now, each LPT and RPT go through 16 rounds of encryption process each with its own key.
• At the end, LPT and RPT are re-joined and a final permutation is performed on combined block.

Each of the 16 rounds, in turn consists of these steps:

During expansion permutation, it goes to S- box substitution after doing XOR of 48 bit key with 48 bit right plain text. S- Box produces the 32-bit output using substitution technique. Then a straight permutation is done. These 32 bits are permuted using P- box.

Advanced Encryption Standard (AES) keys are symmetric keys that can be three different key lengths (128, 192, or 256 bits).

• Assume intruder, hears and accurately copies down the complete ciphertext
• However, unlike the intended recipient, he does not know what the decryption key is and so cannot decrypt the ciphertext easily
• If the intruder can only listen to the communication channel and cannot modify the message, then such an intruder is passive intruder
• If the intruder can listen to the communication channel also record messages and play them back later, inject his own messages, or modify legitimate messages before they get to the receiver then such an intruder is active intruder
• Therefore, active intruder as well as passive intruder can read the message, but only active intruder can modify it

Proxy firewalls operate at the application layer to filter incoming traffic between your network and the traffic source hence, the name “application-level gateway.”. The proxy firewall first establishes a connection to the source of the traffic and inspects the incoming data packet.

In asymmetric key cryptography each node has 2 keys private key and public key public key is as the name suggests is public that is known to sender while the private key held by the receiver which decrypts the data encrypted by sender using public key of receiver.

The correct answer is Encryption.

Key Points

• Encryption is the process of converting plain text into a coded format, known as ciphertext, to prevent unauthorized access.
• It is a crucial aspect of data security, ensuring that sensitive information remains confidential during transmission or storage.
• Encryption algorithms use keys to transform data, and the same or a different key is used to decrypt the information back to its original form.
• Types of encryption include symmetric encryption, where the same key is used for both encryption and decryption, and asymmetric encryption, which uses a pair of keys (public and private).
• Common encryption standards include AES (Advanced Encryption Standard), RSA (Rivest-Shamir-Adleman), and DES (Data Encryption Standard).

Additional Information

• Decryption is the reverse process of encryption, converting ciphertext back into readable plain text using a key.
• Encryption is widely used in various applications, including online banking, email communications, and securing personal data on devices.
• The strength of encryption depends on the algorithm used and the length of the encryption key; longer keys generally provide stronger security.

The correct answer is Authentication.

Key Points

• MAC stands for message authentication code.
• A message authentication code is an authentication tag (also called a checksum) derived by application of an authentication scheme, together with a secret key, to a message.
• MACs can be categorized as - 
  • Unconditionally secure
  • Hash function-based
  • Stream cipher based
  • Block cipher based

Concept -

In columnar transposition cipher,

• The message is written out in rows of a fixed length, and then read out again column by column.
• Width of the rows and the permutation of the columns are usually defined by the keyword.
• The word TOMATO is of length 6 so the rows are of length 6, and the permutation is defined by the lexicographical order of the letters in the keyword.  (A - 1, M - 2, O - 3, T - 4)
• Any spare spaces are filled with nulls or left blank or placed by a character (Example: *).
• Finally, the message is read off in columns, in the order specified by the keyword.

 

Explanation -

T	O	M	A	T	O
4	3	2	1	4	3
t	h	e	t	o	m
a	t	o	i	s	a
p	l	a	n	t	i
n	t	h	e	n	i
g	h	t	s	h	a
d	e	f	a	m	i
l	y	*	*	*	*
5th	3rd	2nd	1st	6th	4th

Writing column wise:

TINESAX / EOAHTFX / HTLTHEY / MAIIAIX / TAPNGDL / OSTNHMX

Concept:

In a symmetric key cryptographic system, both parties have access to the key. So, the first person has N-1 keys with other N-1 people, the second one has another N-2 with N-2 people (since 1 is already considered) and so on till 1.

Formula

\(\sum_{i =1}^{i=n} =\frac{n(n+1)}{2}\)

Calculation

Total number of keys required = 1 + 2 + 3 + … + (N – 2) + (N – 1)

where n = N – 1  

\(\sum_{i =1}^{i=N-1}=\frac{N -1((N -1) +1)}{2} = \frac{N(N-1)}{2}\)