dao.php

<?php 
public function getBlindIndex($string)
	{
    $index_key = base64_decode($this->index_key);
    return bin2hex(
        sodium_crypto_pwhash(
            32,
            $string,
            $index_key,
            SODIUM_CRYPTO_PWHASH_OPSLIMIT_MODERATE,
            SODIUM_CRYPTO_PWHASH_MEMLIMIT_MODERATE
        )
    );
	}