Random Number Generation
The random API subsystem provides random number generation APIs in both cryptographically and non-cryptographically secure instances. Which random API to use is based on the cryptographic requirements of the random number. The non-cryptographic APIs will return random values much faster if non-cryptographic values are needed.
The cryptographically secure random functions shall be compliant to the FIPS 140-2 [NIST02] recommended algorithms. Hardware based random-number generators (RNG) can be used on platforms with appropriate hardware support. Platforms without hardware RNG support shall use the CTR-DRBG algorithm. The algorithm can be provided by TinyCrypt or mbedTLS depending on your application performance and resource requirements.
Note
The CTR-DRBG generator needs an entropy source to establish and maintain the cryptographic security of the PRNG.
Kconfig Options
These options can be found in the following path subsys/random/Kconfig.
CONFIG_TEST_RANDOM_GENERATORFor testing, this option allows a non-random number generator to be used and permits random number APIs to return values that are not truly random.
The random number generator choice group allows selection of the RNG source function for the system via the RNG_GENERATOR_CHOICE choice group. An override of the default value can be specified in the SOC or board .defconfig file by using:
choice RNG_GENERATOR_CHOICE
default XOSHIRO_RANDOM_GENERATOR
endchoice
The random number generators available include:
CONFIG_TIMER_RANDOM_GENERATORenables number generator based on system timer clock. This number generator is not random and used for testing only.
CONFIG_ENTROPY_DEVICE_RANDOM_GENERATORenables a random number generator that uses the enabled hardware entropy gathering driver to generate random numbers.
CONFIG_XOSHIRO_RANDOM_GENERATORenables 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 cryptographically secure random number generator source function. An override of the default value can be specified in the SOC or board .defconfig file by using:
choice CSPRNG_GENERATOR_CHOICE
default CTR_DRBG_CSPRNG_GENERATOR
endchoice
The cryptographically secure random number generators available include:
CONFIG_HARDWARE_DEVICE_CS_GENERATORenables a cryptographically secure random number generator using the hardware random generator driver
CONFIG_CTR_DRBG_CSPRNG_GENERATORenables the CTR-DRBG pseudo-random number generator. The CTR-DRBG is a FIPS140-2 recommended cryptographically secure random number generator.
Personalization data can be provided in addition to the entropy source to make the initialization of the CTR-DRBG as unique as possible.
CONFIG_CS_CTR_DRBG_PERSONALIZATIONCTR-DRBG Initialization Personalization string