Remove the notion of counting entropy bits in HMAC_RNG or Randpool.

Instead simply consider the PRNG seeded if a poll kicked off from reseed
met its goal, or if the user adds data.

Doing anything else prevents creating (for instance) a PRNG seeded with
64 bits of entropy, which is unsafe for some purposes (key generation)
but quite possibly safe enough for others (generating salts and such).

2 files changed, 8 insertions, 18 deletions

diff --git a/src/rng/randpool/randpool.cpp b/src/rng/randpool/randpool.cpp
index 98b088808..af36c335f 100644
--- a/src/rng/randpool/randpool.cpp
+++ b/src/rng/randpool/randpool.cpp
@@ -116,8 +116,8 @@ void Randpool::reseed(u32bit poll_bits)
    xor_buf(pool, mac_val, mac_val.size());
    mix_pool();
 
-   entropy = std::min<u32bit>(entropy + accum.bits_collected(),
-                              8 * mac_val.size());
+   if(accum.bits_collected() >= poll_bits)
+      seeded = true;
    }
 
 /**
@@ -129,8 +129,8 @@ void Randpool::add_entropy(const byte input[], u32bit length)
    xor_buf(pool, mac_val, mac_val.size());
    mix_pool();
 
-   // Assume 1 bit conditional entropy per byte of input
-   entropy = std::min<u32bit>(entropy + length, 8 * mac_val.size());
+   if(length)
+      seeded = true;
    }
 
 /**
@@ -142,14 +142,6 @@ void Randpool::add_entropy_source(EntropySource* src)
    }
 
 /**
-* Check if the the pool is seeded
-*/
-bool Randpool::is_seeded() const
-   {
-   return (entropy >= 7 * mac->OUTPUT_LENGTH);
-   }
-
-/**
 * Clear memory of sensitive data
 */
 void Randpool::clear() throw()
@@ -159,7 +151,7 @@ void Randpool::clear() throw()
    pool.clear();
    buffer.clear();
    counter.clear();
-   entropy = 0;
+   seeded = false;
    }
 
 /**
@@ -198,7 +190,7 @@ Randpool::Randpool(BlockCipher* cipher_in,
    buffer.create(BLOCK_SIZE);
    pool.create(POOL_BLOCKS * BLOCK_SIZE);
    counter.create(12);
-   entropy = 0;
+   seeded = false;
    }
 
 /**
@@ -211,8 +203,6 @@ Randpool::~Randpool()
 
    std::for_each(entropy_sources.begin(), entropy_sources.end(),
                  del_fun<EntropySource>());
-
-   entropy = 0;
    }
 
 }
diff --git a/src/rng/randpool/randpool.h b/src/rng/randpool/randpool.h
index 46683934e..f44527609 100644
--- a/src/rng/randpool/randpool.h
+++ b/src/rng/randpool/randpool.h
@@ -20,7 +20,7 @@ class BOTAN_DLL Randpool : public RandomNumberGenerator
    {
    public:
       void randomize(byte[], u32bit);
-      bool is_seeded() const;
+      bool is_seeded() const { return seeded; }
       void clear() throw();
       std::string name() const;
 
@@ -43,7 +43,7 @@ class BOTAN_DLL Randpool : public RandomNumberGenerator
 
       std::vector<EntropySource*> entropy_sources;
       SecureVector<byte> pool, buffer, counter;
-      u32bit entropy;
+      bool seeded;
    };
 
 }