INTRODUCTION TO CRYPTOGRAPHY - D334
QUESTIONS AND ANSWERS WITH SOLUTIONS 2025
version
XOR the following
0101110101010111
1001100000111010
------------------ - ANSWER-1100010101101101
asymmetric key-based encryption
-typical methods - ANSWER-RSA
DSA
El Gamal
Symmetric key-based encryption
-Typical Methods - ANSWER-RC2- 40 bit key size 64 bit block
RC4- (Stream Cipher)- Used in SSL and WEP
RC5- (Variable Key size, 32, 64, or 128 bit block size)
AES- (128, 192 or 256 bit key size, 128 bit block size)
DES- (56 bit key size. 64 bit Block size)
3DES- (112 bit key size, 64 bit block size)
Block Encryption - ANSWER-RC2(40 bit key size)
RC5(Variable block size)
IDEA
DES
3DES
AES (Rijndael)
Blowfish
twofish
stream encryption - ANSWER-RC4
Chacha
Rainbow Attack - ANSWER-The method of knowing the mapping between the hashed values and the
original data
Dictionary-type attack - ANSWER-a brute force analysis
∉ - ANSWER-does not belong to
when an object is not in a set
∈ - ANSWER-Belongs to
when an object is within a set
⊆ - ANSWER-subset
subset has fewer elements or equal to the set
A ∪ B - ANSWER-union (objects that belong to set A or set B)
| - ANSWER-such that
,A ∩ B - ANSWER-Intersection: in both A and B
Enigma Machine -Cypher 10 - ANSWER-Used a polyalphabetic substitution cipher, which did not
repeat within a reasonable time period, along with a secret key. For the cracking of the Enigma cipher,
the challenge was thus to determine both the algorithm used and the key. Enigma's main weakness,
though, was that none of the plain text letters could be ciphered as itself.
Four-square cipher9 - ANSWER-Uses four 5 × 5 matrices arranged in a square, are where each matrix
contains 25 letters for encoding and decoding operations.
One-time pad cypher8 - ANSWER-Cypher Code mapping that is only used once.
Advantage: it is essentially unbreakable.
Disadvantage: it takes lots of work as you would have to generate the pad to be used, each time.
Vigenere Cipher 7 - ANSWER-Polyalphabetic cipher that involves using a different mapping, based on
a keyword, for each character of the cipher. An advantage of this type of cipher is that the same
plaintext character is likely to be coded to different mappings, depending on the position of the
keyword, making guessing more difficult.
Ceasar Cipher6 - ANSWER-Mono-alphabetic substitution cipher known as "shift" cipher. Involves
plaintext being replaced by a letter some fixed number of positions down the alphabet. i.e., a Caesar
Cipher using a shift of +3 would mean a plaintext letter A would result in a ciphertext letter D (a shift
of three positions to the right in the alphabet)
Morse Code cipher 5 - ANSWER-Encoding method, rather than a cipher, that works by translating
characters into sequences of dots (.) and dashes (-)
Playfair Cipher 4 - ANSWER-5 × 5 matrix containing the alphabet less the letter J. Cipher/decipher
process consists of a set of rules outlining use of column and row combinations.
BIFID Cipher 3 - ANSWER-Makes use of a grid and which maps the letters into numeric values.
Rail Code Cipher 2 - ANSWER-Employs a method to scramble text by writing it in a sequence across a
number of rails.
Pig Pen Cipher 1 - ANSWER-Mono- alphabetic substitution cipher that makes use of mapping plaintext
characters to graphical characters rather than to alphabetic ones. i.e. A=(pick a symbol), vs A=(pick a
letter). Disadvantage: once the mapping is known, it is difficult to keep the message secret.
Encryption - ANSWER-in simplest terms is changing plaintext into ciphertext
Decryption - ANSWER-The process of converting a ciphertext into plaintext.
AESCrypt - ANSWER-Encrypt individual files and encrypt full disks with options such as Bitlocker and
FileVault
Mono-alphabetic - ANSWER-c code or substitution is where a single mapping from our alphabet to a
cipher alphabet is created. Many early cryptosystems used this.
Polyalphabetic - ANSWER-refers to the mapping of our alphabet to a number of cipher alphabets. This
approach added a bit of complexity to early cryptosystems.
One-time pad - ANSWER-is considered to be unbreakable since it only uses its cipher code once.
Pseudo-Random Number Generators (PRNGs) - ANSWER-This method repeats the random numbers
after a given time (periodic). They are fast and are also deterministic and are useful in producing a
repeatable set of random numbers.
, Frequency Analysis - ANSWER-is cipher cracking methodology that involves identifying patterns and
variations in the probability of codes. i.e. a three-letter ciphered text combination spotted at the
beginning of a string too often could tip us off that those three letters correlate the letters THE in the
English alphabet.
True Random Number Generators (TRNGs) - ANSWER-This method generates a true random number
and uses some form of random process. One approach is to monitor the movements of a mouse
pointer on a screen or from the pauses between keystrokes. Overall, the method is generally slow,
especially if it involves human interaction, but is non-deterministic and aperiodic.
Entropy - ANSWER-measures level of unpredictability; in encryption relates to the degree of
uncertainty of the encryption process.
ASCII - ANSWER-8-bit values, up to 256 characters
UTF-16 - ANSWER-16- bit values, up to 65,536 characters
Hardware vs Software encryption - ANSWER-Hardware encryption is more efficient than software
encryption.
Hardware Security Module (HSM) - ANSWER-is a tamper-evident and intrusion-resistant physical
device that safeguards and manages cryptographic keys and provides cryptographic processing.
Trusted Platform Module (TPM) - ANSWER-is a dedicated processor that handles hardware-level
encryption; allows the use of full disk encryption on a hard drive in a manner that minimizes the
impact on system performance. TPM contains the encryption keys.
Combination vs. Permutation - ANSWER-combinations = not concerned with the order//permutations
= all options considered including sequence.
Secret Key - ANSWER-encryption (symmetric Cryptography) makes use of a single secret key for both
encryption and decryption.
Diffie-Hellman - ANSWER-is a widely used key exchange algorithm used to exchange the secret key in
symmetric cryptography.
Two types of symmetric encryption - ANSWER-block and stream
Symmetric block encryption - ANSWER--involves grouping data into blocks and encrypting the
individual blocks
-padding is used to fill blocks to operating size when the data does not fit perfectly.
symmetric stream encryption - ANSWER--involves encrypting one bit at a time, i.e., a synchronous
stream
-is often much faster than block and can typically be applied in real-time applications.
Symmetric block ciphers - ANSWER--manage how blocks of data are processed through block cipher
mode implementations. For instance, one may choose to use the DES block cipher configured with
ECB as the mode of operation.
Common Block Cipher Modes - ANSWER-Electronic Code Book (ECB)
Cipher Block Chaining (CBC)
QUESTIONS AND ANSWERS WITH SOLUTIONS 2025
version
XOR the following
0101110101010111
1001100000111010
------------------ - ANSWER-1100010101101101
asymmetric key-based encryption
-typical methods - ANSWER-RSA
DSA
El Gamal
Symmetric key-based encryption
-Typical Methods - ANSWER-RC2- 40 bit key size 64 bit block
RC4- (Stream Cipher)- Used in SSL and WEP
RC5- (Variable Key size, 32, 64, or 128 bit block size)
AES- (128, 192 or 256 bit key size, 128 bit block size)
DES- (56 bit key size. 64 bit Block size)
3DES- (112 bit key size, 64 bit block size)
Block Encryption - ANSWER-RC2(40 bit key size)
RC5(Variable block size)
IDEA
DES
3DES
AES (Rijndael)
Blowfish
twofish
stream encryption - ANSWER-RC4
Chacha
Rainbow Attack - ANSWER-The method of knowing the mapping between the hashed values and the
original data
Dictionary-type attack - ANSWER-a brute force analysis
∉ - ANSWER-does not belong to
when an object is not in a set
∈ - ANSWER-Belongs to
when an object is within a set
⊆ - ANSWER-subset
subset has fewer elements or equal to the set
A ∪ B - ANSWER-union (objects that belong to set A or set B)
| - ANSWER-such that
,A ∩ B - ANSWER-Intersection: in both A and B
Enigma Machine -Cypher 10 - ANSWER-Used a polyalphabetic substitution cipher, which did not
repeat within a reasonable time period, along with a secret key. For the cracking of the Enigma cipher,
the challenge was thus to determine both the algorithm used and the key. Enigma's main weakness,
though, was that none of the plain text letters could be ciphered as itself.
Four-square cipher9 - ANSWER-Uses four 5 × 5 matrices arranged in a square, are where each matrix
contains 25 letters for encoding and decoding operations.
One-time pad cypher8 - ANSWER-Cypher Code mapping that is only used once.
Advantage: it is essentially unbreakable.
Disadvantage: it takes lots of work as you would have to generate the pad to be used, each time.
Vigenere Cipher 7 - ANSWER-Polyalphabetic cipher that involves using a different mapping, based on
a keyword, for each character of the cipher. An advantage of this type of cipher is that the same
plaintext character is likely to be coded to different mappings, depending on the position of the
keyword, making guessing more difficult.
Ceasar Cipher6 - ANSWER-Mono-alphabetic substitution cipher known as "shift" cipher. Involves
plaintext being replaced by a letter some fixed number of positions down the alphabet. i.e., a Caesar
Cipher using a shift of +3 would mean a plaintext letter A would result in a ciphertext letter D (a shift
of three positions to the right in the alphabet)
Morse Code cipher 5 - ANSWER-Encoding method, rather than a cipher, that works by translating
characters into sequences of dots (.) and dashes (-)
Playfair Cipher 4 - ANSWER-5 × 5 matrix containing the alphabet less the letter J. Cipher/decipher
process consists of a set of rules outlining use of column and row combinations.
BIFID Cipher 3 - ANSWER-Makes use of a grid and which maps the letters into numeric values.
Rail Code Cipher 2 - ANSWER-Employs a method to scramble text by writing it in a sequence across a
number of rails.
Pig Pen Cipher 1 - ANSWER-Mono- alphabetic substitution cipher that makes use of mapping plaintext
characters to graphical characters rather than to alphabetic ones. i.e. A=(pick a symbol), vs A=(pick a
letter). Disadvantage: once the mapping is known, it is difficult to keep the message secret.
Encryption - ANSWER-in simplest terms is changing plaintext into ciphertext
Decryption - ANSWER-The process of converting a ciphertext into plaintext.
AESCrypt - ANSWER-Encrypt individual files and encrypt full disks with options such as Bitlocker and
FileVault
Mono-alphabetic - ANSWER-c code or substitution is where a single mapping from our alphabet to a
cipher alphabet is created. Many early cryptosystems used this.
Polyalphabetic - ANSWER-refers to the mapping of our alphabet to a number of cipher alphabets. This
approach added a bit of complexity to early cryptosystems.
One-time pad - ANSWER-is considered to be unbreakable since it only uses its cipher code once.
Pseudo-Random Number Generators (PRNGs) - ANSWER-This method repeats the random numbers
after a given time (periodic). They are fast and are also deterministic and are useful in producing a
repeatable set of random numbers.
, Frequency Analysis - ANSWER-is cipher cracking methodology that involves identifying patterns and
variations in the probability of codes. i.e. a three-letter ciphered text combination spotted at the
beginning of a string too often could tip us off that those three letters correlate the letters THE in the
English alphabet.
True Random Number Generators (TRNGs) - ANSWER-This method generates a true random number
and uses some form of random process. One approach is to monitor the movements of a mouse
pointer on a screen or from the pauses between keystrokes. Overall, the method is generally slow,
especially if it involves human interaction, but is non-deterministic and aperiodic.
Entropy - ANSWER-measures level of unpredictability; in encryption relates to the degree of
uncertainty of the encryption process.
ASCII - ANSWER-8-bit values, up to 256 characters
UTF-16 - ANSWER-16- bit values, up to 65,536 characters
Hardware vs Software encryption - ANSWER-Hardware encryption is more efficient than software
encryption.
Hardware Security Module (HSM) - ANSWER-is a tamper-evident and intrusion-resistant physical
device that safeguards and manages cryptographic keys and provides cryptographic processing.
Trusted Platform Module (TPM) - ANSWER-is a dedicated processor that handles hardware-level
encryption; allows the use of full disk encryption on a hard drive in a manner that minimizes the
impact on system performance. TPM contains the encryption keys.
Combination vs. Permutation - ANSWER-combinations = not concerned with the order//permutations
= all options considered including sequence.
Secret Key - ANSWER-encryption (symmetric Cryptography) makes use of a single secret key for both
encryption and decryption.
Diffie-Hellman - ANSWER-is a widely used key exchange algorithm used to exchange the secret key in
symmetric cryptography.
Two types of symmetric encryption - ANSWER-block and stream
Symmetric block encryption - ANSWER--involves grouping data into blocks and encrypting the
individual blocks
-padding is used to fill blocks to operating size when the data does not fit perfectly.
symmetric stream encryption - ANSWER--involves encrypting one bit at a time, i.e., a synchronous
stream
-is often much faster than block and can typically be applied in real-time applications.
Symmetric block ciphers - ANSWER--manage how blocks of data are processed through block cipher
mode implementations. For instance, one may choose to use the DES block cipher configured with
ECB as the mode of operation.
Common Block Cipher Modes - ANSWER-Electronic Code Book (ECB)
Cipher Block Chaining (CBC)
