Hi!
Randomness again. Sorry if I just missed some relevant discussion
xoshiro** has a known edge case: all-zero seed
<?php
$engine = new \Random\Engine\Xoshiro256StarStar(str_repeat("\0", 32));
while (true) {
echo hex2bin($engine->generate()), PHP_EOL; // 0000000000000000
}
It should be documented and/or handled
It's only for a string seed, int seed is not affected
--
Anton
2022年8月4日(木) 17:10 Anton Smirnov sandfox@sandfox.me:
Hi!
Randomness again. Sorry if I just missed some relevant discussion
xoshiro** has a known edge case: all-zero seed
<?php
$engine = new \Random\Engine\Xoshiro256StarStar(str_repeat("\0", 32));
while (true) {
echo hex2bin($engine->generate()), PHP_EOL; // 0000000000000000
}It should be documented and/or handled
It's only for a string seed, int seed is not affected
--
Anton--
To unsubscribe, visit: https://www.php.net/unsub.php
Hi.
Thanks for the report! This is dangerous behavior and we will attempt to
fix it for 8.2beta3.
Best regards
Go Kudo
Hi
xoshiro** has a known edge case: all-zero seed
Indeed, good catch. I had that in mind, but forgot about it.
<?php
$engine = new \Random\Engine\Xoshiro256StarStar(str_repeat("\0", 32));
while (true) {
echo hex2bin($engine->generate()), PHP_EOL; // 0000000000000000
}It should be documented and/or handled
It's only for a string seed, int seed is not affected
I've created a PR here:
https://github.com/php/php-src/pull/9250
I've opted to throw a ValueError in that case, as that's the only safe
option that does not introduce a bias.
The 32xNUL seed basically should only happen for manually written
testing input and not happen otherwise. An actual random seed will
result in 32 NUL bytes with just a 2**-256 chance and when relying on
the implicit CSPRNG seeding (null as seed parameter) my PR will just
retry to catch even that edge case.
Best regards
Tim Düsterhus
dangerous to be sure, but it's also a technically valid seed,
are you sure we should disallow a valid seed?
Hi
xoshiro** has a known edge case: all-zero seed
Indeed, good catch. I had that in mind, but forgot about it.
<?php
$engine = new \Random\Engine\Xoshiro256StarStar(str_repeat("\0", 32));
while (true) {
echo hex2bin($engine->generate()), PHP_EOL; // 0000000000000000
}It should be documented and/or handled
It's only for a string seed, int seed is not affected
I've created a PR here:
https://github.com/php/php-src/pull/9250
I've opted to throw a ValueError in that case, as that's the only safe
option that does not introduce a bias.The 32xNUL seed basically should only happen for manually written
testing input and not happen otherwise. An actual random seed will
result in 32 NUL bytes with just a 2**-256 chance and when relying on
the implicit CSPRNG seeding (nullas seed parameter) my PR will just
retry to catch even that edge case.Best regards
Tim Düsterhus--
To unsubscribe, visit: https://www.php.net/unsub.php
On Thu, Aug 4, 2022 at 1:33 PM Hans Henrik Bergan divinity76@gmail.com
wrote:
dangerous to be sure, but it's also a technically valid seed,
are you sure we should disallow a valid seed?
How is it a valid seed if it creates invalid outputs?
dangerous to be sure, but it's also a technically valid seed,
are you sure we should disallow a valid seed?
Reference implementation defines it as invalid:
https://prng.di.unimi.it/xoshiro256starstar.c
Some implementations choose to seed the RNG with 0x0000...0001 but that
kinda inroduces bias
Hi
xoshiro** has a known edge case: all-zero seed
Indeed, good catch. I had that in mind, but forgot about it.
<?php
$engine = new \Random\Engine\Xoshiro256StarStar(str_repeat("\0",
32));while (true) {
echo hex2bin($engine->generate()), PHP_EOL; //
0000000000000000
}It should be documented and/or handled
It's only for a string seed, int seed is not affected
I've created a PR here:
https://github.com/php/php-src/pull/9250
I've opted to throw a ValueError in that case, as that's the only
safe
option that does not introduce a bias.The 32xNUL seed basically should only happen for manually written
testing input and not happen otherwise. An actual random seed will
result in 32 NUL bytes with just a 2**-256 chance and when relying
on
the implicit CSPRNG seeding (nullas seed parameter) my PR will
just
retry to catch even that edge case.Best regards
Tim Düsterhus
Hi
dangerous to be sure, but it's also a technically valid seed,
are you sure we should disallow a valid seed?
The all-zero state is not a valid state as per the reference
implementation at: https://xoshiro.di.unimi.it/xoshiro256starstar.c
The state must be seeded so that it is not everywhere zero.
The period of Xoshiro256** is officially defined to be 2256 - 1
instead of 2256 for that reason.
Best regards
Tim Düsterhus