Obtain tag t

 on the message 0…0,1…1, and output the

tag 

Output the tag 0…0 on the message 0…0,0…0

Obtain tag t

 on the message 0…0,1…1, and output the

tag 

Атака не можлива, схема безпечна

This looks like the

authenticate-then-encrypt approach using CBC-mode and CBC-MAC (with the same

key) -- but here it's ok, since CBC-MAC is applied to something random

This is an example of

the encrypt-then-authenticate approach using (a variant of) CTR-mode and

CBC-MAC, so is secure

This can be viewed as an

example of the encrypt-and-authenticate approach using CBC-mode and CBC-MAC (with

the same key), and is insecure

This looks like the

encrypt-then-authenticate approach using (a variant of) CTR-mode and CBC-MAC,

except that here the same key is being used for both; this looks insecure!