How should I store my sha512 salted & hashed passw

问题:

All,

I am using the following PHP function to salt & hash user passwords for a web app:

function stringHashing($password,$salt){
 $hashedString=$password.$salt;
 for ($i=0; $i<50; $i++){
  $hashedString=hash('sha512',$password.$hashedString.$salt);
  }
 return $hashedString;
}  

What is the best way to store the resulting string in MySQL? I suppose it is a fixed CHAR field? How should I go about calculating the right length?

Thanks,

JDelage

回答1:

Well, SHA512 will always return a 512 bit hash, the two-argument hash() method returns this as hex digits, so that's 512 bits / 8 bits per byte * 2 hex digits per byte = 128 hex digits

A CHAR(128) should be what you need

回答2:

I have always used a varchar field with a more-than-needed length. What if, down the road, you want to change your algorithm? You have to alter the table, which is annoying.

SHA512 will produce a 128 char string, so give the field at least that.

Also, I must point out that you are doing a lot of wasted processing. You are not adding too much security by iterating through the same salt and hash over and over and over again. Ultimately, you will still need a salt and password, everything else about the algorithm remains constant.

回答3:

If someone knows your salt, they probably have your source code which guides them to repeat it 50 times. In that light, given the trivial security benefit to recursive re-hashing with a fixed-count, I thought I'd suggest using SHA2() from MySQL 5.5.5+ as a neater alternative:

mysql_query("SELECT SHA2(CONCAT('$password','$salt'), 512) AS `hash`;");

Which will be your VARCHAR(128) ready to INSERT/UPDATE.