Which of the following is not true about a hash value.
Similarly to a digital signature, a hash value can guarantee the integrity of a document (i.e. once the document is changed, the hash value of the original document won't match the modified document, but is fixed in length no matter how long the document is).
The hash function (the calculation of hash value) is known to the public.
For the same document, if we use the same hash function, we should produce the same hash value.
To verify a hash value we need to obtain the private key of the creator of the hash value.