Cryptography Fundamentals Questions and Answers

Q: Encrypt “INTERNET” using transposition cipher with the following key :3 5 2 1 41 2 3 4 5

The cipher text is TRNIE TZENZ.Split the plaintext into blocks of five, padding the last with Z: INTER and NETZZ. The key's top row tells which plaintext position goes into each cipher position: the first cipher letter is plaintext letter 3, then 5, 2, 1 and 4.INTER: letters 3, 5, 2, 1, 4 are T, R, N, I, E, giving TRNIE. NETZZ: letters 3, 5, 2, 1, 4 are T, Z, E, N, Z, giving TZENZ.The other options are wrong arrangements: (B) simply swaps the two padded blocks, and (A) and (C) do not follow the key's order of positions.

Q: Encryption transforms data to

Encryption transforms data into cipher text.Encryption applies an algorithm and a key to readable plain text, producing unreadable cipher text. Only someone with the right key can reverse it by decryption to recover the plain text. That reversibility with a key is what separates encryption from other transformations.Plain text is the input to encryption, not its output. Hash values come from hashing, a one-way function with no key that cannot be reversed. Metadata is data about data, such as a file's size or timestamps.

Q: Match the following cryptographic algorithms with their design issues :List - IList - IIa. DESi. Message Digestb. AESii. Public Keyc. RSAiii. 56-bit keyd. SHA- 1iv. 128-bit keyCodes : a b c d

The match is a-iii, b-iv, c-ii, d-i.DES uses a 56-bit key, AES uses a 128-bit key, RSA is a public key algorithm and SHA-1 produces a message digest.Code (C) gives these four. The other codes swap the key sizes or the public key and digest roles. DES was designed with a 56-bit effective key and is now considered weak, AES is the replacement with 128, 192 or 256-bit keys, RSA relies on a public and a private key, and SHA-1 maps a message to a 160-bit digest, which is why it is matched with message digest.

Encrypt “INTERNET” using transposition cipher with the following key :

3 5 2 1 4
1 2 3 4 5

A.RINTE ZZNET
B.ZZNET INTER
C.ETRNI NZETZ
D.TRNIE TZENZ

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: D

The cipher text is TRNIE TZENZ.

Split the plaintext into blocks of five, padding the last with Z: INTER and NETZZ. The key's top row tells which plaintext position goes into each cipher position: the first cipher letter is plaintext letter 3, then 5, 2, 1 and 4.

INTER: letters 3, 5, 2, 1, 4 are T, R, N, I, E, giving TRNIE. NETZZ: letters 3, 5, 2, 1, 4 are T, Z, E, N, Z, giving TZENZ.

The other options are wrong arrangements: (B) simply swaps the two padded blocks, and (A) and (C) do not follow the key's order of positions.

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Encryption transforms data to

A.Plain text
B.Cipher text
C.Metadata
D.Hash values

Exam Year(s)

Tripura Public Service Commission - 2026,

Answer: B

Encryption transforms data into cipher text.

Encryption applies an algorithm and a key to readable plain text, producing unreadable cipher text. Only someone with the right key can reverse it by decryption to recover the plain text. That reversibility with a key is what separates encryption from other transformations.

Plain text is the input to encryption, not its output. Hash values come from hashing, a one-way function with no key that cannot be reversed. Metadata is data about data, such as a file's size or timestamps.

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Data Encryption Techniques are particularly used for ______.

A.protecting data in Data Communication System.
B.reduce Storage Space Requirement.
C.enhances Data Integrity.
D.decreases Data Integrity.

Exam Year(s)

UGC NET - 2012,

Answer: A

Data encryption techniques are used for protecting data in a data communication system. The data is converted to a form that cannot be read without the key, so it is safe while it travels on the network and from tapping.

Encryption does not reduce the storage space (compression does that), and it does not itself improve or decrease data integrity, which is the task of checks like checksums and hashes. So the other options are wrong.

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Find the false statement :

A.In Modern Cryptography, symmetric key algorithms use same key both for Encryption and Decryption.
B.The symmetric cipher DES (Data Encryption Standard) was widely used in the industry for security product.
C.The AES (Advanced Encryption Standard) cryptosystem allows variable key lengths of size 56 bits and 124 bits.
D.Public key algorithms use two different keys for Encryption and Decryption.

Exam Year(s)

UGC NET - 2013,

Answer: C

The false statement is the one about AES key lengths. The Advanced Encryption Standard supports fixed key lengths of 128, 192 and 256 bits, not variable lengths of 56 and 124 bits. The 56-bit key belongs to DES.

The other statements are true: symmetric algorithms use the same key to encrypt and decrypt, DES was widely used in security products, and public key algorithms use a different key for each of encryption and decryption.

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In ________ substitution, a character in the plaintext is always changed to the same character in the ciphertext, regardless of its position in the text.

A.polyalphabetic
B.monoalphabetic
C.transpositional
D.multialphabetic

Exam Year(s)

UGC NET - 2013,

Answer: B

In a monoalphabetic substitution a character in the plaintext is always replaced by the same character in the ciphertext, wherever it occurs, so the answer is (B). The Caesar cipher is the simplest example, with one fixed mapping of the alphabet. In a polyalphabetic substitution, for example the Vigenere cipher, the same plaintext letter can become different ciphertext letters depending on its position, so (A) is the opposite. A transposition cipher does not substitute letters at all, it only rearranges their positions, so (C) is wrong, and multialphabetic in (D) is not a standard term and in any case would not guarantee a single mapping.

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Which of the following substitution technique have the relationship between a character in the plaintext and a character in the ciphertext as one-to-many ?

A.Monoalphabetic
B.Polyalphabetic
C.Transpositional
D.None of the above

Exam Year(s)

UGC NET - 2013,

Answer: B

A polyalphabetic substitution gives a one-to-many relationship, because the same plaintext character can be replaced by different ciphertext characters depending on its position, as in the Vigenere cipher.

In a monoalphabetic substitution each plaintext character always maps to one ciphertext character, which is a one-to-one relationship. A transposition technique does not replace characters at all but only changes their order. Option B is correct. Because of this the frequency pattern of the letters in the plaintext is hidden, which is why the polyalphabetic ciphers are harder to break by frequency analysis.

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Match the following cryptographic algorithms with their design issues :

List - I	List - II
a. DES	i. Message Digest
b. AES	ii. Public Key
c. RSA	iii. 56-bit key
d. SHA- 1	iv. 128-bit key

Codes : a b c d

A.ii i iv iii
B.iii i iv ii
C.iii iv ii i
D.iv i ii iii

Exam Year(s)

UGC NET - 2014,

Answer: C

The match is a-iii, b-iv, c-ii, d-i.

DES uses a 56-bit key, AES uses a 128-bit key, RSA is a public key algorithm and SHA-1 produces a message digest.

Code (C) gives these four. The other codes swap the key sizes or the public key and digest roles. DES was designed with a 56-bit effective key and is now considered weak, AES is the replacement with 128, 192 or 256-bit keys, RSA relies on a public and a private key, and SHA-1 maps a message to a 160-bit digest, which is why it is matched with message digest.

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