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Date: Sun, 30 Apr 2017 08:26:15 +0900
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To: Andrey Andreev <narf@devilix.net>
Cc: Niklas Keller <me@kelunik.com>, Pieter Hordijk <info@pieterhordijk.com>, 
	Joe Watkins <pthreads@pthreads.org>, internals <internals@lists.php.net>, 
	phpdoc <phpdoc@lists.php.net>, Nikita Popov <nikita.ppv@gmail.com>
Content-Type: multipart/alternative; boundary=001a113a1dfaa31202054e56863c
Subject: Re: [PHP-DEV] [RFC][VOTE] Improve hash_hkdf() parameter
From: yohgaki@ohgaki.net (Yasuo Ohgaki)

--001a113a1dfaa31202054e56863c
Content-Type: text/plain; charset=UTF-8

On Sun, Apr 30, 2017 at 8:14 AM, Yasuo Ohgaki <yohgaki@ohgaki.net> wrote:

> I don't need your view of HKDF RFC or usage, but I do need good practical
> examples that justify your point of view. Please don't waste of your/my
> time,
> just give some good examples in next reply. Thanks.
>

BTW, valid (yet not common/proper) example that I can think of is,

<?php
$strong_512bit_key = random_bytes(64);
$strong_256bit_key = hash_hkdf('sha3-512', $strong_512bit_key, 32);
?>

while it does not even require HKDF, though.

<?php
$strong_512bit_key = random_bytes(64);
$strong_256bit_key = hash('sha3-256', $strong_512bit_key);
?>

should be good enough.

Even with "Info", following HMAC is enough.

<?php
$strong_512bit_key = random_bytes(64);
$strong_256bit_key = hash_hmac('sha3-256', $strong_512bit_key, $some_info);
?>

--
Yasuo Ohgaki
yohgaki@ohgaki.net

--001a113a1dfaa31202054e56863c--