Convert byte array to string in PHP

Question

Being new to PHP I need to convert an array of bytes to a string that may be used in php function; hash_hmac("sha256", $payload, $key, true)

The $key will originate from a Guid, say {6fccde28-de32-4c0d-a642-7f0c601d1776}, that's converted to an array of bytes. As hash_hmac takes a string for both data and key I need to convert this byte array without loss due to non-printable chars.

I'm using following PHP code:

function guidToBytes($guid) {
    $guid_byte_order = [3,2,1,0,5,4,6,7,8,9,10,11,12,13,14,15];
    $guid = preg_replace("/[^a-zA-Z0-9]+/", "", $guid);
    $result = [];
    for($i=0;$i<16;$i++)
        $result[] = hexdec(substr($guid, 2 * $guid_byte_order[$i], 2));
    return $result;
}

$payload = utf8_encode("Some data string");
$keyBytes = guidToBytes("6fccde28-de32-4c0d-a642-7f0c601d1776");
$key = implode(array_map("chr", $keyBytes));

$hash = hash_hmac("sha256", $payload, $key, true);
$result = base64_encode($hash);

Equivalent code in c#:

var g = Guid.Parse("6fccde28-de32-4c0d-a642-7f0c601d1776");
var key = g.ToByteArray();
var data = "Some data string";
var payload = Encoding.UTF8.GetBytes(data);

using(var ha = new HMACSHA256(key)) {
   var hash = ha.ComputeHash(payload);
   var result = Convert.ToBase64String(hash);
}

Substituting value in $key will produce same base64 output in both languages, leaving $key to be the thing that's wrong/differs.

So; how do I convert $keyBytes to $key without loss of data?

Answer 1

You can use the chr function in PHP

http://php.net/manual/en/function.chr.php

chr receive in input an int and return a corrispondent ascii char.

$strings = array_map("chr", $bytes);
$string = implode(" ", $strings);

I hope I was helpful