Check in a branch with a major redesign on how entropy polling is performed.

Combine the fast and slow polls, into a single poll() operation.

Instead of being given a buffer to write output into, the EntropySource is
passed an Entropy_Accumulator. This handles the RLE encoding that xor_into_buf
used to do. It also contains a cached I/O buffer so entropy sources do not
individually need to allocate memory for that with each poll. When data
is added to the accumulator, the source specifies an estimate of the number
of bits of entropy per byte, as a double. This is tracked in the accumulator.
Once the estimated entropy hits a target (set by the constructor), the
accumulator's member function predicate polling_goal_achieved flips to true.
This signals to the PRNG that it can stop performing polling on sources,
also polls that take a long time periodically check this flag and return
immediately.

The Win32 and BeOS entropy sources have been updated, but blindly; testing
is needed.

The test_es example program has been modified: now it polls twice and outputs
the XOR of the two collected results. That helps show if the output is consistent
across polls (not a good thing). I have noticed on the Unix entropy source,
occasionally there are many 0x00 bytes in the output, which is not optimal.
This also needs to be investigated.

The RLE is not actually RLE anymore. It works well for non-random inputs
(ASCII text, etc), but I noticed that when /dev/random output was fed into
it, the output buffer would end up being RR01RR01RR01 where RR is a random
byte and 00 is the byte count.

The buffer sizing also needs to be examined carefully. It might be useful
to choose a prime number for the size to XOR stuff into, to help ensure an
even distribution of entropy across the entire buffer space. Or: feed it
all into a hash function?

This change should (perhaps with further modifications) help WRT the
concerns Zack W raised about the RNG on the monotone-dev list.

1 files changed, 14 insertions, 28 deletions

diff --git a/src/entropy/proc_walk/es_ftw.cpp b/src/entropy/proc_walk/es_ftw.cpp
index 1ad6c56b6..406e84cb0 100644
--- a/src/entropy/proc_walk/es_ftw.cpp
+++ b/src/entropy/proc_walk/es_ftw.cpp
@@ -5,7 +5,6 @@
 
 #include <botan/es_ftw.h>
 #include <botan/secmem.h>
-#include <botan/xor_buf.h>
 #include <cstring>
 #include <deque>
 
@@ -110,49 +109,36 @@ FTW_EntropySource::~FTW_EntropySource()
    delete dir;
    }
 
-u32bit FTW_EntropySource::slow_poll(byte buf[], u32bit length)
+void FTW_EntropySource::poll(Entropy_Accumulator& accum)
    {
+   const u32bit MAX_FILES_READ_PER_POLL = 1024;
+
    if(!dir)
       dir = new Directory_Walker(path);
 
-   SecureVector<byte> read_buf(4096);
-
-   u32bit bytes_read = 0;
-   u32bit buf_i = 0;
+   MemoryRegion<byte>& io_buffer = accum.get_io_buffer(2048);
 
-   while(bytes_read < length * 32)
+   for(u32bit i = 0; i != MAX_FILES_READ_PER_POLL; ++i)
       {
       int fd = dir->next_fd();
 
-      if(fd == -1) // re-walk
+      // If we've exhaused this walk of the directory, halt the poll
+      if(fd == -1)
          {
          delete dir;
-         dir = new Directory_Walker(path);
-         fd = dir->next_fd();
-
-         if(fd == -1) // still fails (directory not mounted, etc) -> fail
-            return 0;
+         dir = 0;
+         break;
          }
 
-      ssize_t got = ::read(fd, read_buf.begin(), read_buf.size());
+      ssize_t got = ::read(fd, io_buffer.begin(), io_buffer.size());
+      ::close(fd);
 
       if(got > 0)
-         {
-         buf_i = xor_into_buf(buf, buf_i, length, read_buf, got);
-
-         // never count any one file for more than 128 bytes
-         bytes_read += std::min<u32bit>(got, 128);
-         }
+         accum.add(io_buffer.begin(), got, .005);
 
-      ::close(fd);
+      if(accum.polling_goal_achieved())
+         break;
       }
-
-   return length;
-   }
-
-u32bit FTW_EntropySource::fast_poll(byte[], u32bit)
-   {
-   return 0; // no op
    }
 
 }