MySQL表中的64位密码哈希值

Question

I use this function for hashing my passwords:

// RETURNS: rAyZOnlNBxO2WA53z2rAtFlhdS+M7kec9hskSCpeL6j+WwcuUvfFbpFJUtHvv7ji   
base64_encode(hash_hmac('sha384', $str . SC_NONCE, SC_SITEKEY, true));

And I store hashes in char(64) field (MySQL -InnoDB).

Should I use varchar(64) instead of char(64) ? Why?

Edit: I changed sha256 with sha384 . Because in this example, sha256 always returns 44 bytes for me. Sorry for confusing. Now it's 64-bytes.

Answer 1

varchars save storage by only using up to the length required. If the 64 bit hash is always 64 then it makes no difference in terms of storage so probably char is just as good as varchar in this case.

If you have variable length data to store, then a varchar will save wasting unnecessary space.

Answer 2

You should use CHAR(64) since your hash is fixed in length. Using VARCHAR will add another byte, wasting space.

Answer 3

One of the alternative ways you can do that (if you actually care much about space) is to store the hash in the binary form. Some details of how to do that may be found here ; you'd probably want BINARY(32) for a SHA-256 hash.

Answer 4

Even though you are using a Base 64 encoded string, the result is not necessarily 64 bits in length. In this case, VARCHAR is better because the result can be shorter than 64 bits.

In fact as seen here , 64 bits is the maximum length rather than the set length.