Botan: src/entropy/rdrand/rdrand.cpp Source File

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rdrand.cpp
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1 /*
2 * Entropy Source Using Intel's rdrand instruction
3 * (C) 2012 Jack Lloyd
4 *
5 * Distributed under the terms of the Botan license
6 */
7
8 #include <botan/internal/rdrand.h>
9 #include <botan/cpuid.h>
10
11 #if !defined(BOTAN_USE_GCC_INLINE_ASM)
12 #include <immintrin.h>
13 #endif
14
15 namespace Botan {
16
17 /*
18 * Get the timestamp
19 */
20 void Intel_Rdrand::poll(Entropy_Accumulator& accum)
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 }
59
60 }
Botan::Entropy_Accumulator::add
void add(const void *bytes, size_t length, double entropy_bits_per_byte)
Definition: entropy_src.h:70
Botan::Intel_Rdrand::poll
void poll(Entropy_Accumulator &accum)
Definition: rdrand.cpp:20
Botan
Definition: algo_base.h:14
Botan::CPUID::has_rdrand
static bool has_rdrand()
Definition: cpuid.h:88
Botan::Entropy_Accumulator
Definition: entropy_src.h:19