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You are right about the first part. Sha-256 is a hash function, but it's not symmetric encryption.

symmetric encryption dictates a given key K can be used to both transform plain text into cipher text and vice-versa.

A hashing function cannot be reversed because it's a large to small key space function, meaning it's only one way, there's no reversing a hash, unless you try all possibilities until you get the result.

There are publica tables on some hashing algos, they are giant covering hashs for the most known combinations.

But, a SHA-256 as the name suggests generates a 256-bit output.

Since one bit can be represented with two distincts values (i.e. 0 and 1)

we have all the possible combinations being 2^256 which is a number I not even know the name.

about the string password, that a myth that must fall at any cost.

Humans can NEVER produce strong passwords. It's up to the software engineers and cryptographers to move from a low entropy input to a large entropy input while balancing the computational recurrent cost.

:)

Eloquently put ;)