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?

Alfonso Piscitelli · Accepted Answer · 2017-07-19 09:42:05Z

2

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

edited Jul 19, 2017 at 9:42

answered Jul 19, 2017 at 8:21

Alfonso Piscitelli

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2 Comments

SorenJorgensen Over a year ago

I already do this, however won't array_map "just" produce another array? Outcome then still have to put together in a string?

Alfonso Piscitelli Over a year ago

You can use implode function to obtain a string as result. $strings = array_map("chr", $bytes); $string = implode(" ", $strings);

odan · Accepted Answer · 2017-07-19 09:53:49Z

0

Please try this function to convert a GUID into a binary string:

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

edited Jul 19, 2017 at 9:53

answered Jul 19, 2017 at 8:26

odan

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