A bug in random number generation has been found in AMD processors

Developers have discovered a critical feature in the operation of the hardware random number generator in AMD processors of the Zen 2 architecture. Devices are not capable of generating a value of 0 when using RDRAND and RDSEED instructions, which distinguishes them from similar Intel solutions. The problem was identified during testing of low-level code in assembly language. Unlike the standard behavior of hardware generators, which should provide a uniform distribution of all possible values, AMD chips when executing the specified commands systematically skip the zero result. This creates predictability in chains of random numbers, which is critical for cryptographic operations and security systems. To verify the bug, a test code was provided that allows verifying the absence of zero in the sample. Users on the Hacker News platform confirmed that when running the instructions multiple times on Zen 2 series processors, the probability of getting 0 remains zero, while on Intel processors the value 0 appears with the expected frequency. The lack of ability to generate the full range of numbers can lead to vulnerabilities in pseudorandom number generators (PRNG) that rely on a hardware entropy source. Software developers using RDRAND or RDSEED instructions to generate encryption keys or initialize vectors on systems with AMD processors are recommended to consider this limitation when designing data protection systems.