Substantially change Randpool's reseed logic. Now when a reseed

is requested, Randpool will first do a fast poll on each entropy
source that has been registered. It will count these poll results
towards the collected entropy count, with a maximum of 96
contributed bits of entropy per poll (only /dev/random reaches
this, others measure at 50-60 bits typically), and a maximum of
256 for sum contribution of the fast polls.

Then it will attempt slow polls of all devices until it thinks enough
entropy has been collected (using the rather naive entropy_estimate
function). It will count any slow poll for no more than 256 bits (100 or
so is typical for every poll but /dev/random), and will attempt to collect
at least 512 bits of (estimated/guessed) entropy.

This tends to cause Randpool to use significantly more
sources. Previously it was common, especially on systems with a
/dev/random, for only one or a few sources to be used. This
change helps assure that even if /dev/random and company are
broken or compromised the RNG output remains secure (assuming at
least some amount of entropy unguessable by the attacker can be
collected via other sources).

Also change AutoSeeded_RNG do an automatic poll/seed when it is
created.

2 files changed, 36 insertions, 7 deletions

diff --git a/src/entropy/proc_walk/es_ftw.cpp b/src/entropy/proc_walk/es_ftw.cpp
index ec11378f8..f90d422a5 100644
--- a/src/entropy/proc_walk/es_ftw.cpp
+++ b/src/entropy/proc_walk/es_ftw.cpp
@@ -22,7 +22,7 @@ namespace Botan {
 
 namespace {
 
-class Directory_Walker
+class Directory_Walker : public FTW_EntropySource::File_Descriptor_Source
    {
    public:
       Directory_Walker(const std::string& root) { add_directory(root); }
@@ -93,11 +93,20 @@ int Directory_Walker::next_fd()
 
 }
 
-/*************************************************
-* FTW_EntropySource Constructor                  *
-*************************************************/
+/**
+* FTW_EntropySource Constructor
+*/
 FTW_EntropySource::FTW_EntropySource(const std::string& p) : path(p)
    {
+   dir = 0;
+   }
+
+/**
+* FTW_EntropySource Destructor
+*/
+FTW_EntropySource::~FTW_EntropySource()
+   {
+   delete dir;
    }
 
 /*************************************************
@@ -121,16 +130,25 @@ void FTW_EntropySource::do_slow_poll()
 *************************************************/
 void FTW_EntropySource::poll(u32bit max_read)
    {
-   Directory_Walker dir(path);
+   if(!dir)
+      dir = new Directory_Walker(path);
+
    SecureVector<byte> read_buf(1024);
 
    u32bit read_so_far = 0;
    while(read_so_far < max_read)
       {
-      int fd = dir.next_fd();
+      int fd = dir->next_fd();
 
       if(fd == -1)
-         break;
+         {
+         delete dir;
+         dir = new Directory_Walker(path);
+         fd = dir->next_fd();
+
+         if(fd == -1) // still fails (directory not mounted, etc) -> exit
+            break;
+         }
 
       ssize_t got = ::read(fd, read_buf.begin(), read_buf.size());
 
diff --git a/src/entropy/proc_walk/es_ftw.h b/src/entropy/proc_walk/es_ftw.h
index e0d266141..a0d480aae 100644
--- a/src/entropy/proc_walk/es_ftw.h
+++ b/src/entropy/proc_walk/es_ftw.h
@@ -16,7 +16,17 @@ namespace Botan {
 class BOTAN_DLL FTW_EntropySource : public Buffered_EntropySource
    {
    public:
+      std::string name() const { return "Proc Walker"; }
+
       FTW_EntropySource(const std::string& root_dir);
+      ~FTW_EntropySource();
+
+      class File_Descriptor_Source
+         {
+         public:
+            virtual int next_fd() = 0;
+            virtual ~File_Descriptor_Source() {}
+         };
    private:
       void do_fast_poll();
       void do_slow_poll();
@@ -24,6 +34,7 @@ class BOTAN_DLL FTW_EntropySource : public Buffered_EntropySource
       void poll(u32bit max_read);
 
       const std::string path;
+      File_Descriptor_Source* dir;
    };
 
 }