Cryptography And Network Security Final Exam –
Questions & Verified Answers
Distinguish between symmetric-key and asymmetric-key cryptosystems.
✔️Ans - Aysmmetric key cryptography utilizes two separate keys, a public
and a private key, as opposed to symmetric key cryptography, which only
utilizes one key.
While encryption and decryption in symmetric key cryptography is based
on substitutions and permutations of symbols, encryption in asymmetric
key cryptography is based off of applying mathematical functions to
numbers.
Distinguish between public and private keys in an asymmetric-key
cryptosystem. ✔️Ans - There are two keys used in asymmetric key
cryptography: a public and a private key.
The public key corresponds to encryption and the private key is used in
decryption. The public key is distributed to the community, while the
private key is kept secret and used to decrypt messages encrypted utilizing
the public key.
Distinguish between a one-way function and a trapdoor one-way function.
✔️Ans - A one-way function is any function that satisfies two properties:
1. The function f is simple to compute.
2. The inverse of f is nearly impossible to compute.
This means that the function only goes one way, and cannot be undone by
finding the inverse of the output.
A trapdoor one-way function satisfies a third property:
3. Given the output of f and a trapdoor, or secret, x of f(x) = y can be
computed easily.
Distinguish between message integrity and message authentication.
✔️Ans - Message integrity is the concept that, besides being encrypted, the
integrity of each message needs to be preserved. Meaning that messages
cannot be manipulated or changed by attackers.
Message authentication is the concept that, in addition to sending a
message, the receiver should also receive some form of proof that the
message is coming from the sender instead of an imposter.
, Describe the 3 criteria of cryptographic hash function. ✔️Ans -
Preimage resistance: given a hash function h and y = h(M), it must be
difficult for any attacker to find a message M' such that y = h(M'). This
means that even if an attacker intercepts a message M, they cannot create a
new message M' and pass that message off as M.
Second preimage resistance: even if an attacker gains access to both a
message and a digest, a new message that hashes to the exact same digest
cannot easily be created.
Collision resistance: this ensures that the receiver cannot find two
messages that hash to the same digest. This ensures that false messages
cannot be taken as real messages and ensures message authentication.
List the main features of SHA-512 cryptographic hash function. ✔️Ans -
SHA-512 is word oriented. It creates a digest of 512 bits from a multiple-
block message. Each block is 1024 bits in length,. It utilizes a word-
expansion process to expand each message block. Since the message digest
is 512 bits, SHA-512 could possibly be resistant to all attacks, including
collision.
List three security services provided by the digital signature. ✔️Ans -
Message authentication, message integrity, and nonrepudiation.
Distinguish between data-origin authentication and entity authentication.
✔️Ans - -Entity authentication seeks to let one party verify the identity of
another party. Data-origin authentication only seeks to verify the origin of
a sent message or piece of data.
-Entity-authentication verifies the sender, data-origin authentication
verifies the message.
-Data-origin authentication may not happen in real time, but entity
authentication does.
-Message authentication only authenticates one message and needs to be
repeated for other new messages. Entity authentication authenticates the
claimant for the entire duration of the session.
List the advantages and disadvantages of using long passwords. ✔️Ans -
The longer a password, the less vulnerable it is to being attacked. This is
Questions & Verified Answers
Distinguish between symmetric-key and asymmetric-key cryptosystems.
✔️Ans - Aysmmetric key cryptography utilizes two separate keys, a public
and a private key, as opposed to symmetric key cryptography, which only
utilizes one key.
While encryption and decryption in symmetric key cryptography is based
on substitutions and permutations of symbols, encryption in asymmetric
key cryptography is based off of applying mathematical functions to
numbers.
Distinguish between public and private keys in an asymmetric-key
cryptosystem. ✔️Ans - There are two keys used in asymmetric key
cryptography: a public and a private key.
The public key corresponds to encryption and the private key is used in
decryption. The public key is distributed to the community, while the
private key is kept secret and used to decrypt messages encrypted utilizing
the public key.
Distinguish between a one-way function and a trapdoor one-way function.
✔️Ans - A one-way function is any function that satisfies two properties:
1. The function f is simple to compute.
2. The inverse of f is nearly impossible to compute.
This means that the function only goes one way, and cannot be undone by
finding the inverse of the output.
A trapdoor one-way function satisfies a third property:
3. Given the output of f and a trapdoor, or secret, x of f(x) = y can be
computed easily.
Distinguish between message integrity and message authentication.
✔️Ans - Message integrity is the concept that, besides being encrypted, the
integrity of each message needs to be preserved. Meaning that messages
cannot be manipulated or changed by attackers.
Message authentication is the concept that, in addition to sending a
message, the receiver should also receive some form of proof that the
message is coming from the sender instead of an imposter.
, Describe the 3 criteria of cryptographic hash function. ✔️Ans -
Preimage resistance: given a hash function h and y = h(M), it must be
difficult for any attacker to find a message M' such that y = h(M'). This
means that even if an attacker intercepts a message M, they cannot create a
new message M' and pass that message off as M.
Second preimage resistance: even if an attacker gains access to both a
message and a digest, a new message that hashes to the exact same digest
cannot easily be created.
Collision resistance: this ensures that the receiver cannot find two
messages that hash to the same digest. This ensures that false messages
cannot be taken as real messages and ensures message authentication.
List the main features of SHA-512 cryptographic hash function. ✔️Ans -
SHA-512 is word oriented. It creates a digest of 512 bits from a multiple-
block message. Each block is 1024 bits in length,. It utilizes a word-
expansion process to expand each message block. Since the message digest
is 512 bits, SHA-512 could possibly be resistant to all attacks, including
collision.
List three security services provided by the digital signature. ✔️Ans -
Message authentication, message integrity, and nonrepudiation.
Distinguish between data-origin authentication and entity authentication.
✔️Ans - -Entity authentication seeks to let one party verify the identity of
another party. Data-origin authentication only seeks to verify the origin of
a sent message or piece of data.
-Entity-authentication verifies the sender, data-origin authentication
verifies the message.
-Data-origin authentication may not happen in real time, but entity
authentication does.
-Message authentication only authenticates one message and needs to be
repeated for other new messages. Entity authentication authenticates the
claimant for the entire duration of the session.
List the advantages and disadvantages of using long passwords. ✔️Ans -
The longer a password, the less vulnerable it is to being attacked. This is
