I got confused about key derivation functions. For my project, I need to derive a 128 bits AES encryption key in CTR mode. To do so, I'm using a PBKDF2 to derive this encryption key using an initial information like a password.
PBKDF2 allows me to set its parameters before deriving a key, such as hashing function and iteration number. So, my question is if i set the PBKDF2's hashing function as SHA-256, and specificy the derived key's length as 128 bits, would that be okey? As SHA-256 will hash the input multiple times and produce a hash of 256 bits, how can I get a 128 bits encryption key while having 256 bits output of the SHA-256?