Do cryptographic hash functions reach each possible values, i.e., are they surjective?

Question

Take a commonly used binary hash function - for example, SHA-256. As the name implies, it outputs a 256 bit value.

Let A be the set of all possible 256 bit bina

Answer 1

It is not always the case. However, quality required for an hash algorithm are:

• Cardinality of B
• Repartition of hashes in B (every value in B must have the same probability to be a hash)