Botan  1.10.9
Public Member Functions | List of all members
Botan::Intel_Rdrand Class Reference

#include <rdrand.h>

Inheritance diagram for Botan::Intel_Rdrand:
Botan::EntropySource

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

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.

22 { return "Intel Rdrand"; }
void Botan::Intel_Rdrand::poll ( Entropy_Accumulator accum)
virtual

Perform an entropy gathering poll

Parameters
accumis an accumulator object that will be given entropy

Implements Botan::EntropySource.

Definition at line 20 of file rdrand.cpp.

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

21  {
22  if(!CPUID::has_rdrand())
23  return;
24 
25  /*
26  * Put an upper bound on the total entropy we're willing to claim
27  * for any one polling of rdrand to prevent it from swamping our
28  * poll. Internally, the rdrand system is a DRGB that reseeds at a
29  * somewhat unpredictable rate (the current conditions are
30  * documented, but that might not be true for different
31  * implementations, eg on Haswell or a future AMD chip, so I don't
32  * want to assume). This limit ensures we're going to poll at least
33  * one other source so we have some diversity in our inputs.
34  */
35 
36  const size_t POLL_UPPER_BOUND = 96;
37  const size_t RDRAND_POLLS = 32;
38  const double ENTROPY_PER_POLL =
39  static_cast<double>(POLL_UPPER_BOUND) / (RDRAND_POLLS * 4);
40 
41  for(size_t i = 0; i != RDRAND_POLLS; ++i)
42  {
43  unsigned int r = 0;
44 
45 #if BOTAN_USE_GCC_INLINE_ASM
46  int cf = 0;
47 
48  // Encoding of rdrand %eax
49  asm(".byte 0x0F, 0xC7, 0xF0; adcl $0,%1" :
50  "=a" (r), "=r" (cf) : "0" (r), "1" (cf) : "cc");
51 #else
52  int cf = _rdrand32_step(&r);
53 #endif
54 
55  if(cf == 1)
56  accum.add(r, ENTROPY_PER_POLL);
57  }
58  }
static bool has_rdrand()
Definition: cpuid.h:88
BigInt r
Definition: numthry.cpp:26

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