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RDRAND
RDRAND (for "read random") is an instruction for returning random numbers from an Intel on-chip hardware random number generator which has been seeded by an on-chip entropy source. It is also known as Intel Secure Key Technology, codenamed Bull Mountain. Intel introduced the feature around 2012, and AMD added support for the instruction in June 2015. RDRAND is available in Ivy Bridge processors and is part of the Intel 64 and IA-32 instruction set architectures.
The random number generator is compliant with security and cryptographic standards such as NIST SP 800-90A, FIPS 140-2, and ANSI X9.82. Intel also requested Cryptography Research Inc. to review the random number generator in 2012, which resulted in the paper Analysis of Intel's Ivy Bridge Digital Random Number Generator.
RDSEED is similar to RDRAND and provides lower-level access to the entropy-generating hardware. The RDSEED generator and processor instruction rdseed are available with Intel Broadwell CPUs and AMD Zen CPUs.
The CPUID instruction can be used on both AMD and Intel CPUs to check whether the RDRAND instruction is supported. If it is, bit 30 of the ECX register is set after calling CPUID standard function 01H. AMD processors are checked for the feature using the same test. RDSEED availability can be checked on Intel CPUs in a similar manner. If RDSEED is supported, the bit 18 of the EBX register is set after calling CPUID standard function 07H.
The opcode for RDRAND is 0x0F 0xC7, followed by a ModRM byte that specifies the destination register and optionally combined with a REX prefix in 64-bit mode.
Intel Secure Key is Intel's name for both the RDRAND instruction and the underlying random number generator (RNG) hardware implementation, which was codenamed "Bull Mountain" during development. Intel calls their RNG a "digital random number generator" or DRNG. The generator takes pairs of 256-bit raw entropy samples generated by the hardware entropy source and applies them to an Advanced Encryption Standard (AES) (in CBC-MAC mode) conditioner which reduces them to a single 256-bit conditioned entropy sample. A deterministic random-bit generator called CTR DRBG defined in NIST SP 800-90A is seeded by the output from the conditioner, providing cryptographically secure random numbers to applications requesting them via the RDRAND instruction. The hardware will issue a maximum of 511 128-bit samples before changing the seed value. Using the RDSEED operation provides access to the conditioned 256-bit samples from the AES-CBC-MAC.
The RDSEED instruction was added to Intel Secure Key for seeding another pseudorandom number generator, available in Broadwell CPUs. The entropy source for the RDSEED instruction runs asynchronously on a self-timed circuit and uses thermal noise within the silicon to output a random stream of bits at the rate of 3 GHz, slower than the effective 6.4 Gbit/s obtainable from RDRAND (both rates are shared between all cores and threads). The RDSEED instruction is intended for seeding a software PRNG of arbitrary width, whereas the RDRAND is intended for applications that merely require high-quality random numbers. If cryptographic security is not required, a software PRNG such as Xorshift is usually faster.
On an Intel Core i7-7700K, 4500 MHz (45 × 100 MHz) processor (Kaby Lake-S microarchitecture), a single RDRAND or RDSEED instruction takes 110 ns, or 463 clock cycles, regardless of the operand size (16/32/64 bits). This number of clock cycles applies to all processors with Skylake or Kaby Lake microarchitecture. On the Silvermont microarchitecture processors, each of the instructions take around 1472 clock cycles, regardless of the operand size; and on Ivy Bridge processors RDRAND takes up to 117 clock cycles.
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RDRAND
RDRAND (for "read random") is an instruction for returning random numbers from an Intel on-chip hardware random number generator which has been seeded by an on-chip entropy source. It is also known as Intel Secure Key Technology, codenamed Bull Mountain. Intel introduced the feature around 2012, and AMD added support for the instruction in June 2015. RDRAND is available in Ivy Bridge processors and is part of the Intel 64 and IA-32 instruction set architectures.
The random number generator is compliant with security and cryptographic standards such as NIST SP 800-90A, FIPS 140-2, and ANSI X9.82. Intel also requested Cryptography Research Inc. to review the random number generator in 2012, which resulted in the paper Analysis of Intel's Ivy Bridge Digital Random Number Generator.
RDSEED is similar to RDRAND and provides lower-level access to the entropy-generating hardware. The RDSEED generator and processor instruction rdseed are available with Intel Broadwell CPUs and AMD Zen CPUs.
The CPUID instruction can be used on both AMD and Intel CPUs to check whether the RDRAND instruction is supported. If it is, bit 30 of the ECX register is set after calling CPUID standard function 01H. AMD processors are checked for the feature using the same test. RDSEED availability can be checked on Intel CPUs in a similar manner. If RDSEED is supported, the bit 18 of the EBX register is set after calling CPUID standard function 07H.
The opcode for RDRAND is 0x0F 0xC7, followed by a ModRM byte that specifies the destination register and optionally combined with a REX prefix in 64-bit mode.
Intel Secure Key is Intel's name for both the RDRAND instruction and the underlying random number generator (RNG) hardware implementation, which was codenamed "Bull Mountain" during development. Intel calls their RNG a "digital random number generator" or DRNG. The generator takes pairs of 256-bit raw entropy samples generated by the hardware entropy source and applies them to an Advanced Encryption Standard (AES) (in CBC-MAC mode) conditioner which reduces them to a single 256-bit conditioned entropy sample. A deterministic random-bit generator called CTR DRBG defined in NIST SP 800-90A is seeded by the output from the conditioner, providing cryptographically secure random numbers to applications requesting them via the RDRAND instruction. The hardware will issue a maximum of 511 128-bit samples before changing the seed value. Using the RDSEED operation provides access to the conditioned 256-bit samples from the AES-CBC-MAC.
The RDSEED instruction was added to Intel Secure Key for seeding another pseudorandom number generator, available in Broadwell CPUs. The entropy source for the RDSEED instruction runs asynchronously on a self-timed circuit and uses thermal noise within the silicon to output a random stream of bits at the rate of 3 GHz, slower than the effective 6.4 Gbit/s obtainable from RDRAND (both rates are shared between all cores and threads). The RDSEED instruction is intended for seeding a software PRNG of arbitrary width, whereas the RDRAND is intended for applications that merely require high-quality random numbers. If cryptographic security is not required, a software PRNG such as Xorshift is usually faster.
On an Intel Core i7-7700K, 4500 MHz (45 × 100 MHz) processor (Kaby Lake-S microarchitecture), a single RDRAND or RDSEED instruction takes 110 ns, or 463 clock cycles, regardless of the operand size (16/32/64 bits). This number of clock cycles applies to all processors with Skylake or Kaby Lake microarchitecture. On the Silvermont microarchitecture processors, each of the instructions take around 1472 clock cycles, regardless of the operand size; and on Ivy Bridge processors RDRAND takes up to 117 clock cycles.