Botan::Intel_Rdrand Class Reference

#include <rdrand.h>

Inheritance diagram for Botan::Intel_Rdrand:

Public Member Functions
std::string	name () const
void	poll (Entropy_Accumulator &accum)

Detailed Description

Entropy source using the rdrand instruction first introduced on Intel's Ivy Bridge architecture.

Definition at line 19 of file rdrand.h.

Member Function Documentation

name()

std::string Botan::Intel_Rdrand::name ( ) const

inlinevirtual

Returns

name identifying this entropy source

Implements Botan::EntropySource.

Definition at line 22 of file rdrand.h.

{ return "Intel Rdrand"; }

poll()

void Botan::Intel_Rdrand::poll ( Entropy_Accumulator & accum )

virtual

Perform an entropy gathering poll

Parameters

accum

is an accumulator object that will be given entropy

Implements Botan::EntropySource.

Definition at line 20 of file rdrand.cpp.

   {
   if(!CPUID::has_rdrand())
      return;
 
   /*
   * Put an upper bound on the total entropy we're willing to claim
   * for any one polling of rdrand to prevent it from swamping our
   * poll. Internally, the rdrand system is a DRGB that reseeds at a
   * somewhat unpredictable rate (the current conditions are
   * documented, but that might not be true for different
   * implementations, eg on Haswell or a future AMD chip, so I don't
   * want to assume). This limit ensures we're going to poll at least
   * one other source so we have some diversity in our inputs.
   */
 
   const size_t POLL_UPPER_BOUND = 96;
   const size_t RDRAND_POLLS = 32;
   const double ENTROPY_PER_POLL =
      static_cast<double>(POLL_UPPER_BOUND) / (RDRAND_POLLS * 4);
 
   for(size_t i = 0; i != RDRAND_POLLS; ++i)
      {
      unsigned int r = 0;
 
#if BOTAN_USE_GCC_INLINE_ASM
      int cf = 0;
 
      // Encoding of rdrand %eax
      asm(".byte 0x0F, 0xC7, 0xF0; adcl $0,%1" :
          "=a" (r), "=r" (cf) : "0" (r), "1" (cf) : "cc");
#else
      int cf = _rdrand32_step(&r);
#endif
 
      if(cf == 1)
         accum.add(r, ENTROPY_PER_POLL);
      }
   }

References Botan::Entropy_Accumulator::add(), and Botan::CPUID::has_rdrand().

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The documentation for this class was generated from the following files:

• src/entropy/rdrand/rdrand.h
• src/entropy/rdrand/rdrand.cpp