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random: deprecate XOROSHIRO_RANDOM_GENERATOR

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Deprecate the xoroshiro128+ PRNG algorithm in favour of xoshiro128++.
xoshiro128++ is a drop-in replacement which is invisible from the user
perspective.

xoroshiro128+ is unsuitable because it is explicitly a floating-point
PRNG, not a general-purpose PRNG. This means that the lower 4 bits of
the output are actually linear, not random (from the designers,
https://prng.di.unimi.it/). This means 1/8th of the generated data is
not random.

Additionally, xoroshiro128+ is not a 32bit algorithm, it operates on
64bit numbers. For the vast majority of Zephyr devices, this makes the
PRNG slower than it needs to be. The replacement (xoshiro128++) is
32bit, with no loss in state space (still 128 bit).

Signed-off-by: Jordan Yates <jordan.yates@data61.csiro.au>
This commit is contained in:
Jordan Yates 2021-07-25 19:00:50 +10:00 • committed by Carles Cufí
commit fdeaa9103e
9 changed files with 15 additions and 149 deletions
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6
doc/reference/random/index.rst
View file

@ -42,7 +42,7 @@ An override of the default value can be specified in the SOC or board
.. code-block:: none
choice RNG_GENERATOR_CHOICE
default XOROSHIRO_RANDOM_GENERATOR
default XOSHIRO_RANDOM_GENERATOR
endchoice
The random number generators available include:
@ -55,8 +55,8 @@ The random number generators available include:
enables a random number generator that uses the enabled hardware
entropy gathering driver to generate random numbers.
:kconfig:`CONFIG_XOROSHIRO_RANDOM_GENERATOR`
enables the Xoroshiro128+ pseudo-random number generator, that uses the
:kconfig:`CONFIG_XOSHIRO_RANDOM_GENERATOR`
enables the Xoshiro128++ pseudo-random number generator, that uses the
entropy driver as a seed source.
The CSPRNG_GENERATOR_CHOICE choice group provides selection of the

4
drivers/entropy/Kconfig.rv32m1
View file

@ -12,7 +12,7 @@ config ENTROPY_RV32M1_TRNG
driver based on the RV32M1 TRNG driver.
# Don't use use the RV32M1 TRNG as a random source since it can be quite slow.
# Instead, use the software implemented xoroshiro RNG.
# Instead, use the software implemented xoshiro RNG.
choice RNG_GENERATOR_CHOICE
default XOROSHIRO_RANDOM_GENERATOR if ENTROPY_RV32M1_TRNG
default XOSHIRO_RANDOM_GENERATOR if ENTROPY_RV32M1_TRNG
endchoice

2
soc/arm/nxp_kinetis/kwx/Kconfig.defconfig.mkw40z4
View file

@ -47,7 +47,7 @@ choice CSPRNG_GENERATOR_CHOICE
endchoice
choice RNG_GENERATOR_CHOICE
default XOROSHIRO_RANDOM_GENERATOR
default XOSHIRO_RANDOM_GENERATOR
endchoice
config TINYCRYPT

4
soc/arm/nxp_kinetis/kwx/Kconfig.defconfig.mkw41z4
View file

@ -83,10 +83,10 @@ config TINYCRYPT
#
# KW41Z TRNG entropy source cannot be used as a Hardware RNG source so
# use XOROSHIRO for PRNG
# use XOSHIRO for PRNG
#
choice RNG_GENERATOR_CHOICE
default XOROSHIRO_RANDOM_GENERATOR
default XOSHIRO_RANDOM_GENERATOR
endchoice
endif # SOC_MKW41Z4

6
subsys/random/CMakeLists.txt
View file

@ -2,7 +2,6 @@
if (CONFIG_ENTROPY_DEVICE_RANDOM_GENERATOR OR
CONFIG_TIMER_RANDOM_GENERATOR OR
CONFIG_XOROSHIRO_RANDOM_GENERATOR OR
CONFIG_XOSHIRO_RANDOM_GENERATOR)
zephyr_library()
zephyr_library_sources_ifdef(CONFIG_USERSPACE rand32_handlers.c)
@ -15,8 +14,11 @@ if (CONFIG_TEST_RANDOM_GENERATOR)
Use it carefully.")
endif()
# XOROSHIRO builds the XOSHIRO implementation because a Kconfig choice cannot
# select another choice as a means of deprecating the symbol. Swapping out the
# implementation lets out-of-tree users still build until the symbol is removed.
zephyr_library_sources_ifdef(CONFIG_TIMER_RANDOM_GENERATOR rand32_timer.c)
zephyr_library_sources_ifdef(CONFIG_XOROSHIRO_RANDOM_GENERATOR rand32_xoroshiro128.c)
zephyr_library_sources_ifdef(CONFIG_XOROSHIRO_RANDOM_GENERATOR rand32_xoshiro128.c)
zephyr_library_sources_ifdef(CONFIG_XOSHIRO_RANDOM_GENERATOR rand32_xoshiro128.c)
zephyr_library_sources_ifdef(CONFIG_CTR_DRBG_CSPRNG_GENERATOR rand32_ctr_drbg.c)

11
subsys/random/Kconfig
View file

@ -24,7 +24,7 @@ choice RNG_GENERATOR_CHOICE
If the entropy support of the platform has sufficient performance
to support random request then select that. Otherwise, select the
XOROSHIRO algorithm
XOSHIRO algorithm
config TIMER_RANDOM_GENERATOR
bool "System timer clock based number generator"
@ -44,14 +44,9 @@ config ENTROPY_DEVICE_RANDOM_GENERATOR
number generator source.
config XOROSHIRO_RANDOM_GENERATOR
bool "Use Xoroshiro128+ as PRNG"
depends on ENTROPY_HAS_DRIVER
bool "Use Xoroshiro128+ as PRNG (DEPRECATED)"
help
Enables the Xoroshiro128+ pseudo-random number generator, that uses
the entropy driver as a seed source. This is a fast non-cryptographically
secure random number generator.
It is so named because it uses 128 bits of state.
This is deprecated, please use XOSHIRO_RANDOM_GENERATOR instead.
config XOSHIRO_RANDOM_GENERATOR
bool "Use Xoshiro128++ as PRNG"

122
subsys/random/rand32_xoroshiro128.c
View file

@ -1,122 +0,0 @@
/*
* Copyright (c) 2017 Intel Corporation
*
* SPDX-License-Identifier: CC0-1.0
*
* Based on code written in 2016 by David Blackman and Sebastiano Vigna
* (vigna@acm.org)
*
* To the extent possible under law, the author has dedicated all copyright
* and related and neighboring rights to this software to the public domain
* worldwide. This software is distributed without any warranty.
*
* See <http://creativecommons.org/publicdomain/zero/1.0/>.
*/
/* This is the successor to xorshift128+. It is the fastest full-period
* generator passing BigCrush without systematic failures, but due to the
* relatively short period it is acceptable only for applications with a
* mild amount of parallelism; otherwise, use a xorshift1024* generator.
*
* Beside passing BigCrush, this generator passes the PractRand test suite
* up to (and included) 16TB, with the exception of binary rank tests, as
* the lowest bit of this generator is an LSFR. The next bit is not an
* LFSR, but in the long run it will fail binary rank tests, too. The
* other bits have no LFSR artifacts.
*
* We suggest to use a sign test to extract a random Boolean value, and
* right shifts to extract subsets of bits.
*
* Note that the generator uses a simulated rotate operation, which most C
* compilers will turn into a single instruction. In Java, you can use
* Long.rotateLeft(). In languages that do not make low-level rotation
* instructions accessible xorshift128+ could be faster.
*
* The state must be seeded so that it is not everywhere zero. If you have
* a 64-bit seed, we suggest to seed a splitmix64 generator and use its
* output to fill s.
*/
#include <init.h>
#include <device.h>
#include <drivers/entropy.h>
#include <kernel.h>
#include <string.h>
static uint64_t state[2];
static inline uint64_t rotl(const uint64_t x, int k)
{
return (x << k) | (x >> (64 - k));
}
static int xoroshiro128_initialize(const struct device *dev)
{
dev = device_get_binding(DT_CHOSEN_ZEPHYR_ENTROPY_LABEL);
if (!dev) {
return -EINVAL;
}
int32_t rc = entropy_get_entropy_isr(dev, (uint8_t *)&state,
sizeof(state), ENTROPY_BUSYWAIT);
if (rc == -ENOTSUP) {
/* Driver does not provide an ISR-specific API, assume it can
* be called from ISR context
*/
rc = entropy_get_entropy(dev, (uint8_t *)&state, sizeof(state));
}
if (rc < 0) {
return -EINVAL;
}
return 0;
}
static uint32_t xoroshiro128_next(void)
{
const uint64_t s0 = state[0];
uint64_t s1 = state[1];
const uint64_t result = s0 + s1;
s1 ^= s0;
state[0] = rotl(s0, 55) ^ s1 ^ (s1 << 14);
state[1] = rotl(s1, 36);
return (uint32_t)result;
}
uint32_t z_impl_sys_rand32_get(void)
{
uint32_t ret;
ret = xoroshiro128_next();
return ret;
}
void z_impl_sys_rand_get(void *dst, size_t outlen)
{
uint32_t ret;
uint32_t blocksize = 4;
uint32_t len = 0;
uint32_t *udst = (uint32_t *)dst;
while (len < outlen) {
ret = xoroshiro128_next();
if ((outlen-len) < sizeof(ret)) {
blocksize = outlen - len;
(void)memcpy(udst, &ret, blocksize);
} else {
(*udst++) = ret;
}
len += blocksize;
}
}
/* In-tree entropy drivers will initialize in PRE_KERNEL_1; ensure that they're
* initialized properly before initializing ourselves.
*/
SYS_INIT(xoroshiro128_initialize, PRE_KERNEL_2,
CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);

4
tests/crypto/rand32/prj_hw_random_xoroshiro.conf
View file

@ -1,4 +0,0 @@
CONFIG_ZTEST=y
CONFIG_LOG=y
CONFIG_ENTROPY_GENERATOR=y
CONFIG_XOROSHIRO_RANDOM_GENERATOR=y

5
tests/crypto/rand32/testcase.yaml
View file

@ -6,11 +6,6 @@ tests:
extra_args: CONF_FILE=prj_sw_random_systimer.conf
tags: crypto random security
min_ram: 16
crypto.rand32.random_hw_xoroshiro:
extra_args: CONF_FILE=prj_hw_random_xoroshiro.conf
filter: CONFIG_ENTROPY_HAS_DRIVER
tags: crypto entropy random security
min_ram: 16
crypto.rand32.random_hw_xoshiro:
extra_args: CONF_FILE=prj_hw_random_xoshiro.conf
filter: CONFIG_ENTROPY_HAS_DRIVER