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Date: Thu, 2 Feb 2017 10:18:13 +0100
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To: Yasuo Ohgaki <yohgaki@ohgaki.net>
Cc: =?UTF-8?Q?Lauri_Kentt=C3=A4?= <lauri.kentta@gmail.com>, 
	Tom Worster <fsb@thefsb.org>, "internals@lists.php.net" <internals@lists.php.net>, Leigh <leight@gmail.com>, 
	Nikita Popov <nikita.ppv@gmail.com>
Content-Type: multipart/alternative; boundary=001a114030a4122286054788a5e7
Subject: Re: [PHP-DEV] Re: Improving mt_rand() seed
From: me@kelunik.com (Niklas Keller)

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Content-Type: text/plain; charset=UTF-8

>
> Posting RFC draft before discussion
>
> https://wiki.php.net/rfc/improve_predictable_prng_random
>
> This RFC includes results of recent PRNG related discussions.
> I would like to keep it simple, but basic object feature will be
> implemented.
>
> Methods could raise exceptions for invalid operations rather than ignoring.
>
> Comments?
>
> --
> Yasuo Ohgaki
> yohgaki@ohgaki.net
>

The proposed interface has way too many methods. Nor should CSPRNG extend
the other PRNG interface. And also not the other way round, because then
you can pass a non-CSPRNG to an only CSPRNG-accepting function.

interface RandomInterface {
    public function getInt(int $min = NULL, int $max = NULL); // Int random
    public function getBytes(int $length); // Raw bytes
    public function getString(int $length, int $bits = 6); // String
[0-9a-zA-Z,-]+
    public function seed($seed = NULL); // No use with CS RNG, return TRUE
always.
    public function getState(); // Return string representation PRNG state.
No use with CS RNG, return NULL.
    public function setState(string $state); // Set PRNG state. No use with
CS RNG, return TRUE always.
    public function getCount(); // No use with CS RNG, return 0 always.
    public function getReseedCycle(); // No use with CS RNG, return 0
always.
    public function setReseedCycle(int $count); // No use with CS RNG,
return TRUE always.
}

You can already see from the comments that there are too many methods, e.g.
"No use with CS RNG, return 0 always."

I think the interfaces should look like that:

interface PRNG {
    public function getInt(int $min = null, int $max = null): int;
    public function getBytes(int $length): string;
}

interface SeedablePRNG extends PRNG {
    public function seed(?? $seed): void;
}

interface CSPRNG {
    public function getInt(int $min = null, int $max = null): int;
    public function getBytes(int $length): string;
}

`getString()` should probably be a function accepting a PRNG / CSPRNG and a
string containing possible chars. Maybe also an array, so you can use
non-single-byte encodings like UTF-8.

While getState and setState might be useful to save a state and continue
somewhere in the future with the same state, it's not something for an
interface. If you do something like that, you need the same RNG again, so
those can be exposed only in specific implementations, they shouldn't be in
the interface.

`getCount` and `getReseedCycle`: What's the use case? I think those should
be handled internally, nothing that should be user configurable.

There are also a lot of functions, I don't think we should introduce them.
We can just add static methods with a default instance to each RNG.

Regards, Niklas

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