Move Entropy_Estimator to utils/entropy.h (from anon namespace in HMAC_RNG

implementation), remove freestanding estimate_entropy function, change
Randpool to use entropy estimator.

5 files changed, 130 insertions, 33 deletions

diff --git a/src/utils/entropy.cpp b/src/utils/entropy.cpp
new file mode 100644
index 000000000..1562eb0d2
--- /dev/null
+++ b/src/utils/entropy.cpp
@@ -0,0 +1,80 @@
+/*************************************************
+* Entropy_Estimator Source File                  *
+* (C) 2008 Jack Lloyd                            *
+*************************************************/
+
+#include <botan/entropy.h>
+#include <botan/bit_ops.h>
+
+namespace Botan {
+
+/**
+Update the estimate
+*/
+void Entropy_Estimator::update(const byte buffer[], u32bit length,
+                               u32bit upper_limit)
+   {
+   u32bit this_buf_estimate = 0;
+
+   /*
+   This is pretty naive
+   */
+   for(u32bit j = 0; j != length; ++j)
+      {
+      byte delta = last ^ buffer[j];
+      last = buffer[j];
+
+      byte delta2 = delta ^ last_delta;
+      last_delta = delta;
+
+      byte delta3 = delta2 ^ last_delta2;
+      last_delta2 = delta2;
+
+      byte min_delta = delta;
+      if(min_delta > delta2) min_delta = delta2;
+      if(min_delta > delta3) min_delta = delta3;
+
+      this_buf_estimate += hamming_weight(min_delta);
+      }
+
+   this_buf_estimate /= 2;
+
+   if(upper_limit)
+      estimate += std::min(upper_limit, this_buf_estimate);
+   else
+      estimate += this_buf_estimate;
+   }
+
+/*************************************************
+* Estimate the entropy of the buffer             *
+*************************************************/
+u32bit entropy_estimate(const byte buffer[], u32bit length)
+   {
+   if(length <= 4)
+      return 0;
+
+   u32bit estimate = 0;
+   byte last = 0, last_delta = 0, last_delta2 = 0;
+
+   for(u32bit j = 0; j != length; ++j)
+      {
+      byte delta = last ^ buffer[j];
+      last = buffer[j];
+
+      byte delta2 = delta ^ last_delta;
+      last_delta = delta;
+
+      byte delta3 = delta2 ^ last_delta2;
+      last_delta2 = delta2;
+
+      byte min_delta = delta;
+      if(min_delta > delta2) min_delta = delta2;
+      if(min_delta > delta3) min_delta = delta3;
+
+      estimate += hamming_weight(min_delta);
+      }
+
+   return (estimate / 2);
+   }
+
+}
diff --git a/src/utils/entropy.h b/src/utils/entropy.h
new file mode 100644
index 000000000..24d2fbdbf
--- /dev/null
+++ b/src/utils/entropy.h
@@ -0,0 +1,48 @@
+/*************************************************
+* Entropy_Estimator Header File                  *
+* (C) 2008 Jack Lloyd                            *
+*************************************************/
+
+#ifndef BOTAN_ENTROPY_ESTIMATOR_H__
+#define BOTAN_ENTROPY_ESTIMATOR_H__
+
+#include <botan/types.h>
+#include <algorithm>
+
+namespace Botan {
+
+/**
+Naive Entropy Estimation using first, second, and third order deltas
+
+@todo It would be nice to extend this to test using zlib or bzip2 if
+those modules are compiled in to the library
+*/
+class BOTAN_DLL Entropy_Estimator
+   {
+   public:
+      Entropy_Estimator()
+         { last = last_delta = last_delta2 = 0; estimate = 0; }
+
+      /**
+      Return the current estimate
+      */
+      u32bit value() const { return estimate; }
+
+      /**
+      Set an upper bound on the estimate so far
+      */
+      void set_upper_bound(u32bit upper_limit)
+         { estimate = std::min(estimate, upper_limit); }
+
+      /**
+      Add more entropy data to the current estimation
+      */
+      void update(const byte buffer[], u32bit length, u32bit upper_limit = 0);
+   private:
+      u32bit estimate;
+      byte last, last_delta, last_delta2;
+   };
+
+}
+
+#endif
diff --git a/src/utils/info.txt b/src/utils/info.txt
index b20a16a56..0f0a18a35 100644
--- a/src/utils/info.txt
+++ b/src/utils/info.txt
@@ -19,6 +19,8 @@ charset.cpp
 charset.h
 datastor.cpp
 datastor.h
+entropy.h
+entropy.cpp
 loadstor.h
 mem_ops.h
 mlock.cpp
diff --git a/src/utils/util.cpp b/src/utils/util.cpp
index af1c62ebd..f8b98fcb8 100644
--- a/src/utils/util.cpp
+++ b/src/utils/util.cpp
@@ -64,36 +64,4 @@ u32bit dl_work_factor(u32bit bits)
 #endif
    }
 
-/*************************************************
-* Estimate the entropy of the buffer             *
-*************************************************/
-u32bit entropy_estimate(const byte buffer[], u32bit length)
-   {
-   if(length <= 4)
-      return 0;
-
-   u32bit estimate = 0;
-   byte last = 0, last_delta = 0, last_delta2 = 0;
-
-   for(u32bit j = 0; j != length; ++j)
-      {
-      byte delta = last ^ buffer[j];
-      last = buffer[j];
-
-      byte delta2 = delta ^ last_delta;
-      last_delta = delta;
-
-      byte delta3 = delta2 ^ last_delta2;
-      last_delta2 = delta2;
-
-      byte min_delta = delta;
-      if(min_delta > delta2) min_delta = delta2;
-      if(min_delta > delta3) min_delta = delta3;
-
-      estimate += hamming_weight(min_delta);
-      }
-
-   return (estimate / 2);
-   }
-
 }
diff --git a/src/utils/util.h b/src/utils/util.h
index 62ecb948d..d0e2e110a 100644
--- a/src/utils/util.h
+++ b/src/utils/util.h
@@ -30,7 +30,6 @@ BOTAN_DLL u32bit round_down(u32bit, u32bit);
 /*************************************************
 * Work Factor Estimates                          *
 *************************************************/
-BOTAN_DLL u32bit entropy_estimate(const byte[], u32bit);
 BOTAN_DLL u32bit dl_work_factor(u32bit);
 
 }