Introduction to Cryptography - D334
Questions with complete solution
2025/2026
XOR the following
0101110101010111
1001100000111010
------------------ - correct answer ✔1100010101101101
asymmetric key-based encryption
-typical methods - correct answer ✔RSA
DSA
El Gamal
Symmetric key-based encryption
-Typical Methods - correct 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 - correct answer ✔RC2(40 bit key size)
RC5(Variable block size)
IDEA
,DES
3DES
AES (Rijndael)
Blowfish
twofish
stream encryption - correct answer ✔RC4
Chacha
Rainbow Attack - correct answer ✔The method of knowing the mapping between the hashed values
and the original data
Dictionary-type attack - correct answer ✔a brute force analysis
∉ - correct answer ✔does not belong to
when an object is not in a set
∈ - correct answer ✔Belongs to
when an object is within a set
⊆ - correct answer ✔subset
subset has fewer elements or equal to the set
A ∪ B - correct answer ✔union (objects that belong to set A or set B)
| - correct answer ✔such that
,A ∩ B - correct answer ✔Intersection: in both A and B
Enigma Machine -Cypher 10 - correct 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 - correct 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 - correct 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 - correct 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 - correct 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 - correct answer ✔Encoding method, rather than a cipher, that works by
translating characters into sequences of dots (.) and dashes (-)
Playfair Cipher 4 - correct 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 - correct answer ✔Makes use of a grid and which maps the letters into numeric values.
Rail Code Cipher 2 - correct answer ✔Employs a method to scramble text by writing it in a sequence
across a number of rails.
Pig Pen Cipher 1 - correct 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 - correct answer ✔in simplest terms is changing plaintext into ciphertext
Decryption - correct answer ✔The process of converting a ciphertext into plaintext.
AESCrypt - correct answer ✔Encrypt individual files and encrypt full disks with options such as Bitlocker
and FileVault
Mono-alphabetic - correct 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 - correct 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 - correct answer ✔is considered to be unbreakable since it only uses its cipher code
once.
Pseudo-Random Number Generators (PRNGs) - correct 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.
Questions with complete solution
2025/2026
XOR the following
0101110101010111
1001100000111010
------------------ - correct answer ✔1100010101101101
asymmetric key-based encryption
-typical methods - correct answer ✔RSA
DSA
El Gamal
Symmetric key-based encryption
-Typical Methods - correct 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 - correct answer ✔RC2(40 bit key size)
RC5(Variable block size)
IDEA
,DES
3DES
AES (Rijndael)
Blowfish
twofish
stream encryption - correct answer ✔RC4
Chacha
Rainbow Attack - correct answer ✔The method of knowing the mapping between the hashed values
and the original data
Dictionary-type attack - correct answer ✔a brute force analysis
∉ - correct answer ✔does not belong to
when an object is not in a set
∈ - correct answer ✔Belongs to
when an object is within a set
⊆ - correct answer ✔subset
subset has fewer elements or equal to the set
A ∪ B - correct answer ✔union (objects that belong to set A or set B)
| - correct answer ✔such that
,A ∩ B - correct answer ✔Intersection: in both A and B
Enigma Machine -Cypher 10 - correct 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 - correct 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 - correct 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 - correct 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 - correct 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 - correct answer ✔Encoding method, rather than a cipher, that works by
translating characters into sequences of dots (.) and dashes (-)
Playfair Cipher 4 - correct 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 - correct answer ✔Makes use of a grid and which maps the letters into numeric values.
Rail Code Cipher 2 - correct answer ✔Employs a method to scramble text by writing it in a sequence
across a number of rails.
Pig Pen Cipher 1 - correct 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 - correct answer ✔in simplest terms is changing plaintext into ciphertext
Decryption - correct answer ✔The process of converting a ciphertext into plaintext.
AESCrypt - correct answer ✔Encrypt individual files and encrypt full disks with options such as Bitlocker
and FileVault
Mono-alphabetic - correct 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 - correct 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 - correct answer ✔is considered to be unbreakable since it only uses its cipher code
once.
Pseudo-Random Number Generators (PRNGs) - correct 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.
