Question :
For the remaining questions, consider a 4-bit block cipher, described in hexadecimal by the following table:
|
Plaintext
|
Ciphertext
|
Plaintext
|
Ciphertext
|
|
0
|
a
|
8
|
e
|
|
1
|
c
|
9
|
d
|
|
2
|
f
|
a
|
0
|
|
3
|
6
|
b
|
7
|
|
4
|
3
|
c
|
5
|
|
5
|
8
|
d
|
b
|
|
6
|
4
|
e
|
9
|
|
7
|
2
|
f
|
1
|
You can think of this as a simple substitution cipher for hexadecimal digits. There is no "key" other than the table itself.
Encrypt the 4-block message face using this cipher for each digit individually.
Decrypt the message baab using this cipher.
Why is it insecure to use a block cipher in this way?