random: deprecate XOROSHIRO_RANDOM_GENERATOR

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>

doc/reference/random/index.rst

@@ -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`
+:kconfig:`CONFIG_XOSHIRO_RANDOM_GENERATOR`
- enables the Xoroshiro128+ pseudo-random number generator, that uses the
+ 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

drivers/entropy/Kconfig.rv32m1

@@ -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

soc/arm/nxp_kinetis/kwx/Kconfig.defconfig.mkw40z4

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

soc/arm/nxp_kinetis/kwx/Kconfig.defconfig.mkw41z4

@@ -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

subsys/random/CMakeLists.txt

@@ -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)
 

subsys/random/Kconfig

@@ -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"
+	bool "Use Xoroshiro128+ as PRNG (DEPRECATED)"
-	depends on ENTROPY_HAS_DRIVER
 	help
-	  Enables the Xoroshiro128+ pseudo-random number generator, that uses
+	  This is deprecated, please use XOSHIRO_RANDOM_GENERATOR instead.
-	  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.
 
 config XOSHIRO_RANDOM_GENERATOR
 	bool "Use Xoshiro128++ as PRNG"

subsys/random/rand32_xoroshiro128.c

@@ -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);

tests/crypto/rand32/prj_hw_random_xoroshiro.conf

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

tests/crypto/rand32/testcase.yaml

@@ -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