There are plenty of questions about the difference between AES encryption and hash functions. I read some of them and the general answer is that

1. AES is reversible as long as the key is exposed.
2. AES has fixed input size and hash does not.
3. There is a method to make a hash function based on the block cipher.

I am curious whether there is difference between AES encryption and hash function with the strong assumptions as below:

A. The key of the AES is never exposed. (Without knowing the key, I believe there is no possibility of decryption ans hence one-way function as a hash) B. For some application, the input size is always fixed.

In this case, if someone use the AES encryption as the purpose of hash, is there any possible problems exist?

Thank you for your answering.

There are plenty of questions about the difference between AES encryption and hash functions. I read some of them and the general answer is that

1. AES is reversible as long as the key is exposed.
2. AES has fixed input size and hash does not.
3. There is a method to make a hash function based on the block cipher.

I am curious whether there is a difference between AES encryption and hash function with the strong assumptions as below:

A. The key of the AES is never exposed. (Without knowing the key, I believe there is no possibility of decryption and hence one-way function as a hash)

B. For some applications, the input size is always fixed.

In this case, if someone uses AES encryption as the purpose of hash, do any possible problems exist?