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authorlloyd <[email protected]>2012-05-25 22:52:00 +0000
committerlloyd <[email protected]>2012-05-25 22:52:00 +0000
commit12090a7148d9ee73572cc1a7268fc489504a8173 (patch)
tree51e50ce0852c56231e9e6dc13f168b10edd45d01 /src/entropy/rdrand/rdrand.cpp
parent9594979caf775dc4062850044715b804d1fda60c (diff)
parent65cc04445f8d40497f02a14bd8cb97081790e54b (diff)
propagate from branch 'net.randombit.botan.x509-path-validation' (head 63b5a20eab129ca13287fda33d2d02eec329708f)
to branch 'net.randombit.botan' (head 8b8150f09c55184f028f2929c4e7f7cd0d46d96e)
Diffstat (limited to 'src/entropy/rdrand/rdrand.cpp')
-rw-r--r--src/entropy/rdrand/rdrand.cpp60
1 files changed, 60 insertions, 0 deletions
diff --git a/src/entropy/rdrand/rdrand.cpp b/src/entropy/rdrand/rdrand.cpp
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--- /dev/null
+++ b/src/entropy/rdrand/rdrand.cpp
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+/*
+* 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);
+ }
+ }
+
+}