In a Padding$-$Oracle attack, assume L$=16.$ Which of the following are valid encoded

messages? $($Select all that apply.$)$

a$.0$x$01$ FF $52180404040401$ FF $521804040404$

b$.0$x$01$ FF $52180404040401$ FF $521804040404$

c$.0$x$09090909090909090909090909090909$

d$.0$x$01020304050607080102030405060708$

e$.0$x$01020304050607080102030404040708$

f$.$ None of the above

$8.(6$ points$)$ Which of the following is true when comparing a brute$-$force attack on a block cipher

$($i$.$e$.,$ exhaustive search for the key$)$ to a brute$-$force attack on a hash function $($i$.$e$.,$ using a

birthday attack to find a collision$)?$

a$.$ A block cipher with $256-$bit key provides equivalent security to a hash function with $256-$bit

output.

b$.$ A block cipher with $256-$bit key provides equivalent security to a hash function with $128-$bit

output.

c$.$ A block cipher with $512-$bit key provides equivalent security to a hash function with $1024$ bit

output.

d$.$ A block cipher with $128-$bit key provides equivalent security to a hash function with $1280-$bit

output.

Commented $[$VVP$2]$: Answer is c