1 files changed, 60 insertions, 0 deletions
diff --git a/src/entropy/rdrand/rdrand.cpp b/src/entropy/rdrand/rdrand.cpp
new file mode 100644
index 000000000..51b2bd5f6
--- /dev/null
+++ b/src/entropy/rdrand/rdrand.cpp
@@ -0,0 +1,60 @@
+/*
+* Entropy Source Using Intel's rdrand instruction
+* (C) 2012 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#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;
+
+   /*
+   * 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;
+
+#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);
+      }
+   }
+
+}