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/*
* Entropy Source Using Intel's rdrand instruction
* (C) 2012,2015 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/rdrand.h>
#include <botan/cpuid.h>
#if !defined(BOTAN_USE_GCC_INLINE_ASM)
#include <immintrin.h>
#endif
namespace Botan {
/*
* Get the timestamp
*/
void Intel_Rdrand::poll(Entropy_Accumulator& accum)
{
if(!CPUID::has_rdrand())
return;
/*
Don't consider rdrand as contributing any entropy to the poll. It doesn't
make sense to trust uninspectible hardware.
Even if backdoored, rdrand cannot harm us because the HMAC_RNG poll process
is designed to handle arbitrarily large amounts of attacker known/chosen
input (or even a reseed where every bit we reseeded with was attacker chosen),
as long as at least one seed occured with enough unknown-to-attacker entropy.
*/
const double ENTROPY_ESTIMATE = 0.0;
const size_t RDRAND_POLLS = 32;
for(size_t i = 0; i != RDRAND_POLLS; ++i)
{
unsigned int r = 0;
#if defined(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_ESTIMATE);
}
}
}
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