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RDRAND

Architecture referenceFeex

RDRAND returns random values from the processor's hardware random-number generation facility when a value is available. Software must check its success indication and follow a sound cryptographic design.

What you need to know

RDRAND returns random values from the processor's hardware random-number generation facility when a value is available. Software must check its success indication and follow a sound cryptographic design.

How it works

The instruction writes a value and indicates success with the carry flag. A temporarily unavailable result requires the caller to follow the documented retry or failure policy. The instruction is an interface to a generator, not a replacement for a complete operating-system randomness API and its entropy-management policy.

Where it is useful

An OS or cryptographic runtime can incorporate a hardware randomness source under its documented design. Most application code should request randomness from its maintained OS or library interface, allowing that component to handle availability, composition and platform-specific issues.

How to check support and enablement

CPUID.01H:ECX bit 30 enumerates RDRAND. Every execution must check the carry flag; a register value alone does not prove success. Follow current vendor guidance and the security library's supported implementation.

Use a maintained cryptographic implementation that handles feature selection, failure conditions and the complete algorithm. Hardware acceleration supplies primitives; key management, authentication, nonce rules and protocol choices remain software responsibilities.

What the feature does not establish

RDRAND and RDSEED have different intended interfaces and separate enumeration. A reported feature does not prove a particular application checks failures, nor does it establish a product certification or guarantee that a VM exposes the same randomness implementation as the host.

Compatibility and performance in practice

A feature field is not a product certification or evidence that a particular application is secure. Performance depends on message sizes, mode, batching and the rest of the protocol. Check the actual provider and keep its security updates current.

A practical verification checklist

  1. Record the exact processor or platform model and the application, OS and runtime versions involved. Preserve the wording of the actual error or requirement.
  2. Check the manufacturer reference for that exact model, then inspect the effective capability and enabled state in the environment where the program runs.
  3. Compare every requirement of the selected binary or backend. A similarly named feature, alias or broad technology label is not enough.
  4. Confirm the application selected the intended implementation. Use its documented diagnostics and a supported fallback when requirements are not met.
  5. Make one supported change at a time and repeat the same workload. Keep the original configuration and recovery path available.

If the feature is listed but software cannot use it

Start with the exact failing component. A hardware database describes recorded capability; the operating system or hypervisor can expose a different effective environment. An illegal-instruction error also needs investigation of the actual faulting instruction and binary build, because corruption or an unrelated unsupported instruction can produce a similar symptom.

Install the application, driver or runtime version supported for the exact platform, and use the vendor's documented baseline or fallback build if needed. A software update cannot create an instruction that the processor lacks. Firmware and security-policy changes should follow the system manufacturer's procedure and a recovery plan rather than a generic optimization recipe.

Sources and scope of this explanation

Intel 64 and IA-32 Architectures Software Developer's Manual

These references establish architectural behavior and software requirements. They do not independently verify every feature value on a linked hardware model page. For model support, use that page's manufacturer evidence and check the effective system configuration. This article does not supply a benchmark, certification or independent review date.

Sources and verification

Editorial ownership: Feex. No independent review date is recorded. How we research.

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