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Date: Thu, 7 Jan 2016 10:57:30 -0500
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To: =?UTF-8?Q?Rouven_We=C3=9Fling?= <me@rouvenwessling.de>
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Subject: Re: [PHP-DEV] [RFC] Libsodium
From: scott@paragonie.com (Scott Arciszewski)

On Thu, Jan 7, 2016 at 10:54 AM, Scott Arciszewski <scott@paragonie.com> wr=
ote:
> On Thu, Jan 7, 2016 at 10:52 AM, Rouven We=C3=9Fling <me@rouvenwessling.d=
e> wrote:
>> Hi Scott,
>>
>> questions inline.
>>
>>> On 07 Jan 2016, at 14:26, Scott Arciszewski <scott@paragonie.com> wrote=
:
>>>
>>> I've updated the RFC to make libsodium a core PHP extension in 7.1, to
>>> include references to the online documentation.
>>>
>>> https://wiki.php.net/rfc/libsodium
>>
>> I know this is made difficult by the fact that this is an existing, stab=
le PECL extension, which also supports older PHP versions but I don=E2=80=
=99t think it=E2=80=99s a good idea to introduce more functions that duplic=
ate things handled already in core (I don=E2=80=99t mean in ext-openssl as =
lib sodium would be an alternative to that extension). I=E2=80=99d rather s=
ee less duplication, not more.
>>
>> From a quick glance the following functions seems to be already covered:
>> \Sodium\memcmp
>> \Sodium\bin2hex
>> \Sodium\hex2bin
>> \Sodium\randombytes_buf
>> \Sodium\randombytes_uniform
>> \Sodium\randombytes_random16
>>
>> If their implementation is better than the core implementation, core sho=
uld be fixed.
>>
>> Do the hashing functions have any advantage over those provided by ext-h=
ash?
>>
>> There are also a couple of other functions whose value I=E2=80=99d quest=
ion, I=E2=80=99ll send an email about those later.
>>
>>> This is part of an overall effort to improve PHP's cryptography; up
>>> next will be the pluggable crypto API that supports multiple backends
>>> (with a scope limited to openssl and libsodium at the time of release)
>>> but always provide conservative defaults.
>>
>> A more general question: I haven=E2=80=99t looked at your prototype for =
a higher level API yet, but I=E2=80=99m wondering if it=E2=80=99s still nec=
essary to introduce another low level API? When would I choose to use the l=
atter?
>>
>> Best regards
>> Rouven
>
> The high-level API ties the user's hands and doesn't give them direct
> access to primitives. You can't use it for AES-256-ECB, you can only
> use it for AES-256-CTR+HMAC-SHA-384, with an encoded and
> version-tagged output, for example.
>
> You still need ext/libsodium if you need to use any of its features
> directly, such as \Sodium\memzero().
>
> Scott Arciszewski
> Chief Development Officer
> Paragon Initiative Enterprises <https://paragonie.com>


To clarify: You can swap out AES-256 for AES-192, or SHA-384 for SHA-256, e=
tc.

You cannot swap out the protocol construction for anything other than
Encrypt then MAC.

Scott Arciszewski
Chief Development Officer
Paragon Initiative Enterprises <https://paragonie.com>