RNG changes (GH #593)

Change reseed interval logic to count calls to `randomize` rather than
bytes, to match SP 800-90A

Changes RNG reseeding API: there is no implicit reference to the
global entropy sources within the RNGs anymore. The entropy sources
must be supplied with the API call. Adds support for reseding directly
from another RNG (such as a system or hardware RNG).

Stateful_RNG keeps optional references to both an RNG and a set of
entropy sources. During a reseed, both sources are used if set.
These can be provided to HMAC_DRBG constructor.

For HMAC_DRBG, SP800-90A requires we output no more than 2**16 bytes
per DRBG request. We treat requests longer than that as if the caller
had instead made several sequential maximum-length requests. This
means it is possible for one or more reseeds to trigger even in the
course of generating a single (long) output (generate a 256-bit key
and use ChaCha or HKDF if this is a problem).

Adds RNG::randomize_with_ts_input which takes timestamps and uses them
as the additional_data DRBG field. Stateful_RNG overrides this to also
include the process ID and the reseed counter. AutoSeeded_RNG's
`randomize` uses this.

Officially deprecates RNG::make_rng and the Serialized_RNG construtor
which creates an AutoSeeded_RNG. With these removed, it would be
possible to perform a build with no AutoSeeded_RNG/HMAC_DRBG at all
(eg, for applications which only use the system RNG).

Tests courtesy @cordney in GH PRs #598 and #600

1 files changed, 7 insertions, 27 deletions

diff --git a/src/tests/test_rng.h b/src/tests/test_rng.h
index 6c29b1d55..0379a2ee9 100644
--- a/src/tests/test_rng.h
+++ b/src/tests/test_rng.h
@@ -15,13 +15,6 @@
 #include <botan/hex.h>
 #include <botan/exceptn.h>
 
-#if defined(BOTAN_HAS_SYSTEM_RNG)
-  #include <botan/system_rng.h>
-#else
-  #include <botan/auto_rng.h>
-#endif
-
-
 namespace Botan_Tests {
 
 /**
@@ -43,9 +36,9 @@ class Fixed_Output_RNG : public Botan::RandomNumberGenerator
          return out;
          }
 
-      size_t reseed_with_sources(Botan::Entropy_Sources&,
-                                 size_t,
-                                 std::chrono::milliseconds) override { return 0; }
+      size_t reseed(Botan::Entropy_Sources&,
+                    size_t,
+                    std::chrono::milliseconds) override { return 0; }
 
       void randomize(uint8_t out[], size_t len) override
          {
@@ -87,7 +80,7 @@ class Fixed_Output_RNG : public Botan::RandomNumberGenerator
 class Fixed_Output_Position_RNG : public Fixed_Output_RNG
    {
    public:
-      bool is_seeded() const override { return !m_buf.empty() || m_rng->is_seeded(); }
+      bool is_seeded() const override { return !m_buf.empty() || Test::rng().is_seeded(); }
 
       uint8_t random() override
          {
@@ -114,7 +107,7 @@ class Fixed_Output_Position_RNG : public Fixed_Output_RNG
             }
          else
             { // return random
-               m_rng->randomize(out,len);
+               Test::rng().randomize(out,len);
             }
          }
 
@@ -127,32 +120,19 @@ class Fixed_Output_Position_RNG : public Fixed_Output_RNG
 
       explicit Fixed_Output_Position_RNG(const std::vector<uint8_t>& in, uint32_t pos) :
             Fixed_Output_RNG(in),
-            m_pos(pos),
-            m_rng{}
+            m_pos(pos)
          {
-#if defined(BOTAN_HAS_SYSTEM_RNG)
-   m_rng.reset(new Botan::System_RNG);
-#else
-   m_rng.reset(new Botan::AutoSeeded_RNG);
-#endif
          }
 
       explicit Fixed_Output_Position_RNG(const std::string& in_str, uint32_t pos) :
             Fixed_Output_RNG(in_str),
-            m_pos(pos),
-            m_rng{}
+            m_pos(pos)
          {
-#if defined(BOTAN_HAS_SYSTEM_RNG)
-   m_rng.reset(new Botan::System_RNG);
-#else
-   m_rng.reset(new Botan::AutoSeeded_RNG);
-#endif
          }
 
    private:
       uint32_t m_pos = 0;
       uint32_t m_requests = 0;
-      std::unique_ptr<RandomNumberGenerator> m_rng;
    };
 
 class SeedCapturing_RNG : public Botan::RandomNumberGenerator