Introduction to Cryptography - D334
Final Exam Questions And
Answers(Revised).
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.
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