Random numerical data generator tool9/8/2023 Therefore, in the general case, users and applications should still follow the traditional guidance of using /dev/random when generating long-term cryptographic keys, or use getrandom(2) which by default behaves similarly to /dev/random. On other architectures (specifically, architectures that do not have a fast cycle counter), there is one remaining difference between the two: /dev/random blocks until the kernel has estimated that the CRNGs are properly initialized, whereas /dev/urandom does not. (This is true because the presence of the RDTSC instruction on all x86-64 CPUs means that the CPU-based jitterentropy algorithm will always be able to generate entropy, not to mention that most x86-64 CPUs also support RDRAND.) Since Arch Linux only supports x86-64, /dev/random and /dev/urandom are equivalent on Arch Linux. However, the behavior of /dev/random and /dev/urandom has significantly converged over time, and on x86-64 systems they are now equivalent. Historically, /dev/random was considered to provide stronger random numbers than /dev/urandom. The Linux RNG provides three interfaces for userspace to get random data: Entropy continues to be collected, and the CRNGs are periodically reseeded, as long as the kernel is running. The entropy is extracted using the BLAKE2s cryptographic hash function and used to seed a set of ChaCha20 CRNGs (Cryptographic Random Number Generators) that provide the actual random data. No single entropy source is relied on exclusively. It works by collecting entropy from various sources, such as hardware RNGs, interrupts, and CPU-based jitterentropy. The Linux kernel's built-in RNG produces cryptographically secure pseudorandom data. This page describes the current implementation and behavior, applicable to modern kernels including Arch Linux's officially supported kernels. As such, much information that exists about it is outdated. Note: the Linux RNG has been improved significantly in recent years, with many changes occurring in the 4.x and 5.x kernel series.
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