4B: Encryption

Question 1

what is encryption

Answer 1

the process of scrambling data into a form that cannot be understood by another human unless they have the decrypt key

Question 2

what is decryption

Answer 2

the process of unscrambling data

Question 3

what is the original form of data known as

Answer 3

plaintext

Question 4

what is the encrypted data known as

Answer 4

ciphertext

Question 5

explain what the caeser cipher is

Answer 5

substitutes each letter for another character by simply shifting the letters fowards or backwards

Question 6

why is the caeser cipher easy to crack

Answer 6

because the shift has to be a number between 1 and 25

Question 7

explain the vernam cipher

Answer 7

• plaintext is combined with a one time pad (random sequence of letters) to produce the cipher text
• it is unbreakable

Question 8

explain how you encrypt the word “CAT” using the one time pad “GTS”

Answer 8

• get the ASCII for plain text
• get ASCII for one time pad
• XOR the CG, AT AND TS
• ASCII obtained is ciphertext

Question 9

what is meant by computationally secure

Answer 9

if the cipher cannot be broken using current technology in a timeframe that would be useful

Question 10

explain run length encoding

Answer 10

• it identifies sequences of identical data
• represents these as one data value, a count of how many such values are in the sequence
• eg, if there was 5 green next to eachother it would be 5G

Question 11

explain dictionary based compression

Answer 11

• length strings of symbols are represented by single tokens
• a table is formed using the tokens as keys
• the strings of symbols are used as the entires