Obtaining True Random Numbers with Intel CPUs

Intel built into its third-generation Ivy Bridge Core processors a feature that obtains hardware true random numbers using resistor thermal noise. The principle of the code here is to read a 16-bit random number directly into the rax register via assembly instruction. In 2013, Kyle Condon of the UK launched a petition on Change.org asking maintainer Linus Torvalds to remove RdRand from /dev/random in order to improve kernel security. Because RdRand is an instruction used to generate random numbers, included in the Intel 64 and IA-32 instruction set architectures, and the cryptographic standard it relies on—NIST SP800-90 set by the NSA—is suspected of containing a backdoor. Linus Torvalds responded to the petition swiftly, blasting the petitioners and calling them far too ignorant. Because in Linux systems the random number generator at /dev/random applies further randomization on top of RdRand's random numbers, which not only avoids the possibility of a backdoor but also improves the quality of the generated random numbers.

 

int rdrand16_step(uint16_t *rand)
{
	unsigned char ok;

	/* rdrand dx */
	__asm
	{
		volatile(".byte 0x0f,0xc7,0xf0; setc %1"
		: "=a" (*rand), "=qm" (ok)
			:
			: "dx"
			);
	}

	return ok;
}

 

There are also ready-made JAVA libraries online: https://github.com/cambecc/drnglib