Say we've 16 byte(128 bit) key. So, how many keys would be required?

So, imo. 128 bits key would require 10 rounds

Initial Round(also called add round key), then 10 rounds(including the last round), so we'd require 11 different keys. Am I correct?

 

Why can't you just use the same key again?

 

Say we've 16 byte(128 bit) key. So, how many keys would be required?

So, imo. 128 bits key would require 10 rounds

Initial Round(also called add round key), then 10 rounds(including the last round), so we'd require 11 different keys. Am I correct?

It's been a long time since I looked at AES, but that is my recollection. You would use the key schedule to generate 11 128-bit round keys from the initial 128-bit key.

 

Why can't you just use the same key again?

That would open it up to some pretty serious attacks.