From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: Florian Weimer <fweimer@redhat.com>
Cc: Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>
Subject: Re: [PATCH v6 10/10] manual: Add documentation for arc4random functions
Date: Tue, 28 Jun 2022 16:15:42 -0300 [thread overview]
Message-ID: <ADCA4D82-A8DD-4096-901D-90BDF7FD32E4@linaro.org> (raw)
In-Reply-To: <87czetf0qj.fsf@oldenburg.str.redhat.com>
> On 28 Jun 2022, at 09:09, Florian Weimer <fweimer@redhat.com> wrote:
>
> * Adhemerval Zanella via Libc-alpha:
>
>> +@node High Quality Random
>> +@subsection High Quality Random Number Functions
>> +
>> +This section describes the random number functions provided as a GNU
>> +extension, based on OpenBSD interfaces.
>> +
>> +@Theglibc{} uses kernel entropy obtained either through @code{getrandom}
>> +or by reading @file{/dev/urandom} to seed and periodically re-seed the
>> +internal state. A per-thread data pool is used, which allows fast output
>> +generation.
>> +
>> +Although these functions provide higher random quality than ISO, BSD, and
>> +SVID functions, these still use a Pseudo-Random generator and should not
>> +be used in cryptographic contexts.
>> +
>> +The internal state is cleared and reseed with kernel entropy on @code{fork}
>> +and @code{_Fork} (it is not cleared for either direct @code{clone} syscall
>> +or through glibc wrapper).
>
> “or when using @theglibc{} @code{syscall} funcition”?
Ack, I also removed the sentence from parentheses.
>
>> +The prototypes for these functions are in @file{stdlib.h}.
>> +@pindex stdlib.h
>> +
>> +@deftypefun int32_t arc4random (void)
>> +@standards{GNU, stdlib.h}
>
> Should be BSD, I think. Likewise below.
Ack.
>
>> +@safety{@mtsafe{}@asunsafe{@asucorrupt{}}@acsafe{}}
>> +This function returns a single 32-bit value in the range of 0 to 2^32−1,
>> +which is twice the range of @code{rand} and @code{random}.
>> +@end deftypefun
>
> Can we use @math for the exponent? And please say that the range is
> inclusive.
I changed to use @code, which is what other rand functions use. I added
the inclusive remark as well.
>
>> +@deftypefun uint32_t arc4random_uniform (uint32_t @var{upper_bound})
>> +@standards{GNU, stdlib.h}
>> +@safety{@mtsafe{}@asunsafe{@asucorrupt{}}@acsafe{}}
>> +This function returns a single 32-bit value, uniformly distributed but
>> +less than the @var{upper_bound}. It avoids the @w{modulo bias} when the
>> +upper bound is not a power of two.
>> +
>> +The algorithm obtains the exact sampling of a discrete uniform variable
>> +using an optimal number of random bits for any range @var{upper_bounds},
>> +allowing to consume as less as possible data from the per-thread entropy
>> +pool.
>
> I think this overspecifies the implementation. And we obtain randomness
> in blocks of 8 bits, IIRC, so it's not optimal in our implementation.
Ok, I will remove the last paragraph.
prev parent reply other threads:[~2022-06-28 19:15 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-18 19:14 [PATCH v6 00/10] Add arc4random support Adhemerval Zanella
2022-05-18 19:14 ` [PATCH v6 01/10] stdlib: Add arc4random, arc4random_buf, and arc4random_uniform (BZ #4417) Adhemerval Zanella
2022-06-02 9:44 ` Yann Droneaud
2022-06-10 17:26 ` Adhemerval Zanella
2022-05-18 19:14 ` [PATCH v6 02/10] stdlib: Add arc4random tests Adhemerval Zanella
2022-06-28 11:59 ` Florian Weimer
2022-06-28 16:58 ` Adhemerval Zanella
2022-05-18 19:14 ` [PATCH v6 03/10] benchtests: Add arc4random benchtest Adhemerval Zanella
2022-06-28 12:01 ` Florian Weimer
2022-06-28 17:06 ` Adhemerval Zanella
2022-06-28 17:13 ` Noah Goldstein
2022-06-28 17:14 ` Noah Goldstein
2022-06-28 17:22 ` Adhemerval Zanella
2022-05-18 19:14 ` [PATCH v6 04/10] aarch64: Add optimized chacha20 Adhemerval Zanella
2022-06-28 12:03 ` Florian Weimer
2022-06-28 17:39 ` Adhemerval Zanella
2022-05-18 19:14 ` [PATCH v6 05/10] x86: Add SSE2 " Adhemerval Zanella
2022-05-18 20:44 ` Noah Goldstein
2022-05-18 19:14 ` [PATCH v6 06/10] x86: Add AVX2 " Adhemerval Zanella
2022-05-18 19:14 ` [PATCH v6 07/10] powerpc64: Add " Adhemerval Zanella
2022-05-18 19:14 ` [PATCH v6 08/10] s390x: " Adhemerval Zanella
2022-05-18 19:14 ` [PATCH v6 09/10] stdlib: Add TLS optimization to arc4random Adhemerval Zanella
2022-06-28 12:19 ` Florian Weimer
2022-06-28 19:45 ` Adhemerval Zanella
2022-05-18 19:14 ` [PATCH v6 10/10] manual: Add documentation for arc4random functions Adhemerval Zanella
2022-06-28 12:09 ` Florian Weimer
2022-06-28 19:15 ` Adhemerval Zanella [this message]
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