How long is the SHA256 hash?

问题

I'm going to run SHA256 on a password + salt, but I don't know how long to make my VARCHAR when setting up the MySQL database. What is a good length?

回答1:

A sha256 is 256 bits long -- as its name indicates.

If you are using an hexadecimal representation, each digit codes for 4 bits ; so you need 64 digits to represent 256 bits -- so, you need a varchar(64), or a char(64), as the length is always the same, not varying at all.

And the demo :

$hash = hash('sha256', 'hello, world!');
var_dump($hash);

Will give you :

$ php temp.php
string(64) "68e656b251e67e8358bef8483ab0d51c6619f3e7a1a9f0e75838d41ff368f728"

i.e. a string with 64 characters.

回答2:

Encoding options for SHA256's 256 bits:

1. Base64: 6 bits per char = CHAR(44) including padding character
2. Hex: 4 bits per char = CHAR(64)
3. Binary: 8 bits per byte = BINARY(32)

回答3:

I prefer to use BINARY(32) since it's the optimized way!

You can place in that 32 hex digits from (00 to FF).

Therefore BINARY(32)!

回答4:

Why would you make it VARCHAR? It doesn't vary. It's always 64 characters, which can be determined by running anything into one of the online SHA-256 calculators.

回答5:

It will be fixed 64 chars, so use char(64)

来源：https://stackoverflow.com/questions/2240973/how-long-is-the-sha256-hash