| (a) |
What is a monoalphabetic substitution cipher?
|
[2] |
| (b) |
How does a polyalphabetic substitution cipher differ from a monoalphabetic one?
|
[1] |
| (c) |
What is it that makes a polyalphabetic substitution cipher more secure than a monoalphabetic cipher?
|
[2] |
| (d) |
Explain the difference between a block cipher and a stream cipher. Which is the more secure?
|
[2] |
| (e) |
Explain how to decrypt a monoalphabetic substitution cipher.
|
[4] |
| (f) |
Decrypt the following extract from a block of ciphertext. nxlotpqyrgmld pd ksq It is English text, encrypted using a monoalphabetic cipher. The complete ciphertext had the frequency distribution, in letters per thousand,
For reference, the frequency distribution of ordinary English text, also in letters per thousand, is
Show your working. |
[4] |
