php - How to generate a random, long salt for use in hashing?

Question

What is a way in PHP to make a random, variable length salt for use in hashing? Let's say I want to make a 16-character long salt - how would I do it?

Answer 1

edit: the mcrypt extension has been deprecated. For new projects take a look at
random_bytes ( int $length )
and the sodium (as of php 7.2 core-)extension.

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If the mcrypt extension is available you could simply use mcrypt_create_iv(size, source) to create a salt.

$iv = mcrypt_create_iv(16, MCRYPT_DEV_URANDOM);
var_dump($iv);

Since each byte of the "string" can be in the range between 0-255 you need a binary-safe function to save/retrieve it.