INTRODUCTION TO CRYPTOGRAPHY, D830 LATEST
ACTUAL EXAM WITH VERIFIED QUESTIONS & CORRECT
ANSWERS
Question 1.
shift cipher
ANSWER
is a substitution cipher which replaces a plaintext's letter by a letter that is a fixed
number of positions to the right of the letter in the alphabet. For a shift cipher, the
fixed number of positions is the encryption key.
Question 2.
Trapdoor function
ANSWER
information is known, but difficult otherwise.
Question 3.
Cryptographic primitive
ANSWER
Question 4.
Message authentication, or data origin authentication
ANSWER
authentication security service implies the message integrity.
,Question 5.
Confusion
ANSWER
of an encryption key impacts most of the ciphertext bits. The confusion property
hides the relationship between a ciphertext and the encryption key.
Question 6.
key
ANSWER
is a string of bits
Question 7.
Output Feedback (OFB)
ANSWER
mode a block cipher generates keystream blocks which are XORed with the
plaintext blocks to create the ciphertext blocks. Chaining dependencies do not
exist in OFB mode because each block is created independently of plaintext and
ciphertext blocks. In OFB mode encryption and decryption processes are the
same and errors do not propagate.
Question 8.
Encryption
ANSWER
Encryption uses an algorithm and a key to hide the meaning of a message.
Encryption can be symmetric or asymmetric. In asymmetric encryption two
different, but mathematically related keys are used for encryption and decryption.
In symmetric encryption the same key is used for encryption and decryption.
Symmetric encryption can use stream or block ciphers. A stream cipher encrypts
d
, Question 9.
Jefferson's wheel cipher.
ANSWER
In the late 1700s, Thomas Jefferson came up with a cipher system similar to that of
Vigenere, but with higher security, because it has much more combinations to
select keys. As illustrated by Figure 2.3.3, Jefferson's cylinder is composed of 36
disks (or wells), stacked on top of each other around an axle. The 26 Latin letters
are randomly inscribed on each disk. The disks are numbered; they are removable
and can be mounted on the axle in any desired order. The order of disk mounting
mount the disks in the same way.
Question 10.
padding
ANSWER
The process of adding bits to a plaintext's last block. Ex: If a block cipher's block
size is 64 bits, an 84-bit plaintext is split into one block of 64 bits and a second
block of 20 bits. The second block is padded with '64 - 20' or 44 random bits to
create a 64-bit block.
Question 11.
Ancient Egypt
ANSWER
The earliest known encrypted text found in Egypt dates back to (nearly) 1900 BC.
Hieroglyphics on pharaohs and dignitaries tombs had been hiding secrets, and
were disclosed (nearly) four millennia later. Secrets were represented as symbols
(i.e. hieroglyphics), unreadable to those who did not (and still do not) know the
hieroglyphics alphabet.
Question 12.
Information-theoretic secure cipher
ANSWER
a cipher is information-theoretic secure if it cannot be broken even if the
adversary has unlimited computation resources.
ACTUAL EXAM WITH VERIFIED QUESTIONS & CORRECT
ANSWERS
Question 1.
shift cipher
ANSWER
is a substitution cipher which replaces a plaintext's letter by a letter that is a fixed
number of positions to the right of the letter in the alphabet. For a shift cipher, the
fixed number of positions is the encryption key.
Question 2.
Trapdoor function
ANSWER
information is known, but difficult otherwise.
Question 3.
Cryptographic primitive
ANSWER
Question 4.
Message authentication, or data origin authentication
ANSWER
authentication security service implies the message integrity.
,Question 5.
Confusion
ANSWER
of an encryption key impacts most of the ciphertext bits. The confusion property
hides the relationship between a ciphertext and the encryption key.
Question 6.
key
ANSWER
is a string of bits
Question 7.
Output Feedback (OFB)
ANSWER
mode a block cipher generates keystream blocks which are XORed with the
plaintext blocks to create the ciphertext blocks. Chaining dependencies do not
exist in OFB mode because each block is created independently of plaintext and
ciphertext blocks. In OFB mode encryption and decryption processes are the
same and errors do not propagate.
Question 8.
Encryption
ANSWER
Encryption uses an algorithm and a key to hide the meaning of a message.
Encryption can be symmetric or asymmetric. In asymmetric encryption two
different, but mathematically related keys are used for encryption and decryption.
In symmetric encryption the same key is used for encryption and decryption.
Symmetric encryption can use stream or block ciphers. A stream cipher encrypts
d
, Question 9.
Jefferson's wheel cipher.
ANSWER
In the late 1700s, Thomas Jefferson came up with a cipher system similar to that of
Vigenere, but with higher security, because it has much more combinations to
select keys. As illustrated by Figure 2.3.3, Jefferson's cylinder is composed of 36
disks (or wells), stacked on top of each other around an axle. The 26 Latin letters
are randomly inscribed on each disk. The disks are numbered; they are removable
and can be mounted on the axle in any desired order. The order of disk mounting
mount the disks in the same way.
Question 10.
padding
ANSWER
The process of adding bits to a plaintext's last block. Ex: If a block cipher's block
size is 64 bits, an 84-bit plaintext is split into one block of 64 bits and a second
block of 20 bits. The second block is padded with '64 - 20' or 44 random bits to
create a 64-bit block.
Question 11.
Ancient Egypt
ANSWER
The earliest known encrypted text found in Egypt dates back to (nearly) 1900 BC.
Hieroglyphics on pharaohs and dignitaries tombs had been hiding secrets, and
were disclosed (nearly) four millennia later. Secrets were represented as symbols
(i.e. hieroglyphics), unreadable to those who did not (and still do not) know the
hieroglyphics alphabet.
Question 12.
Information-theoretic secure cipher
ANSWER
a cipher is information-theoretic secure if it cannot be broken even if the
adversary has unlimited computation resources.
