RDRAND

RDRAND is an instruction available in x86 processors from Intel and AMD that generates random numbers. It was introduced by Intel in 2012 with the Ivy Bridge microarchitecture and subsequently adopted by AMD. RDRAND is designed to provide a hardware-based source of cryptographically secure pseudo-random numbers directly to software.

The instruction retrieves random numbers from an on-chip hardware random number generator (HRNG). This generator typically employs a digital circuit that amplifies thermal noise, creating unpredictable variations. The raw output of the noise source is then conditioned through a deterministic random bit generator (DRBG) to meet cryptographic standards. The DRBG is responsible for ensuring the output is statistically sound and resistant to known attacks.

RDRAND has several advantages over software-based pseudo-random number generators (PRNGs). Because the random numbers are generated in hardware, they are often faster and more efficient than software implementations. Moreover, they are intended to provide higher security because the source of randomness is based on physical phenomena rather than algorithms, which can be vulnerable to compromise.

The quality and security of RDRAND output depend critically on the implementation of the HRNG and DRBG. While RDRAND is designed to meet stringent security requirements, concerns have been raised about the potential for vulnerabilities if the hardware is compromised or if there are design flaws in the generation process. Independent audits and testing are crucial to ensure the continued integrity of RDRAND as a reliable source of entropy. If RDRAND fails, it sets the CPU Carry Flag (CF) to 1. When the instruction is successful, CF is set to 0, and the generated random number is stored in a general-purpose register.