Refactor RNG seeding logic in command line interface

This is needed for LLVM which doesn't have any usable entropy
sources. Also useful for determinsitic private key creation, etc.

2 files changed, 81 insertions, 69 deletions

diff --git a/src/cli/cli.h b/src/cli/cli.h
index fcff94870..23cf0ff1c 100644
--- a/src/cli/cli.h
+++ b/src/cli/cli.h
@@ -11,14 +11,6 @@
 #include <botan/parsing.h>
 #include <botan/rng.h>
 
-#if defined(BOTAN_HAS_AUTO_SEEDING_RNG)
-   #include <botan/auto_rng.h>
-#endif
-
-#if defined(BOTAN_HAS_SYSTEM_RNG)
-   #include <botan/system_rng.h>
-#endif
-
 #include <fstream>
 #include <iostream>
 #include <functional>
@@ -30,6 +22,10 @@
 
 namespace Botan_CLI {
 
+/* Declared in utils.cpp */
+std::unique_ptr<Botan::RandomNumberGenerator>
+cli_make_rng(const std::string& type, const std::string& hex_drbg_seed);
+
 class CLI_Error : public std::runtime_error
    {
    public:
@@ -334,11 +330,12 @@ class Command
          m_spec_opts.insert(std::make_pair("error-output", ""));
 
 #if defined(BOTAN_HAS_SYSTEM_RNG)
-         const auto availableRng = "system";
+         const std::string availableRng = "system";
 #else
-         const auto availableRng = "auto";
+         const std::string availableRng = "user";
 #endif
          m_spec_opts.insert(std::make_pair("rng-type", availableRng));
+         m_spec_opts.insert(std::make_pair("drbg-seed", ""));
          }
 
       /*
@@ -493,29 +490,7 @@ class Command
          {
          if(m_rng == nullptr)
             {
-            const std::string rng_type = get_arg("rng-type");
-
-            if(rng_type == "system")
-               {
-#if defined(BOTAN_HAS_SYSTEM_RNG)
-               m_rng.reset(new Botan::System_RNG);
-#endif
-               }
-
-            // TODO --rng-type=drbg
-            // TODO --drbg-seed=hexstr
-
-            if(rng_type == "auto")
-               {
-#if defined(BOTAN_HAS_AUTO_SEEDING_RNG)
-               m_rng.reset(new Botan::AutoSeeded_RNG);
-#endif
-               }
-
-            if(!m_rng)
-               {
-               throw CLI_Error_Unsupported("rng", rng_type);
-               }
+            m_rng = cli_make_rng(get_arg("rng-type"), get_arg("drbg-seed"));
             }
 
          return *m_rng.get();
diff --git a/src/cli/utils.cpp b/src/cli/utils.cpp
index 2bf03c760..620ef72a2 100644
--- a/src/cli/utils.cpp
+++ b/src/cli/utils.cpp
@@ -29,6 +29,10 @@
    #include <botan/rdrand_rng.h>
 #endif
 
+#if defined(BOTAN_HAS_HMAC_DRBG)
+   #include <botan/hmac_drbg.h>
+#endif
+
 #if defined(BOTAN_HAS_HTTP_UTIL)
    #include <botan/http_util.h>
 #endif
@@ -47,6 +51,64 @@
 
 namespace Botan_CLI {
 
+std::unique_ptr<Botan::RandomNumberGenerator>
+cli_make_rng(const std::string& rng_type, const std::string& hex_drbg_seed)
+   {
+#if defined(BOTAN_HAS_SYSTEM_RNG)
+   if(rng_type == "system")
+      {
+      return std::unique_ptr<Botan::RandomNumberGenerator>(new Botan::System_RNG);
+      }
+#endif
+
+#if defined(BOTAN_HAS_RDRAND_RNG)
+   if(rng_type == "rdrand")
+      {
+      if(Botan::CPUID::has_rdrand())
+         return std::unique_ptr<Botan::RandomNumberGenerator>(new Botan::RDRAND_RNG);
+      else
+         throw CLI_Error("RDRAND instruction not supported on this processor");
+      }
+#endif
+
+   const std::vector<uint8_t> drbg_seed = Botan::hex_decode(hex_drbg_seed);
+
+#if defined(BOTAN_HAS_AUTO_SEEDING_RNG)
+   if(rng_type == "auto" || rng_type == "entropy")
+      {
+      std::unique_ptr<Botan::RandomNumberGenerator> rng;
+
+      if(rng_type == "entropy")
+         rng.reset(new Botan::AutoSeeded_RNG(Botan::Entropy_Sources::global_sources()));
+      else
+         rng.reset(new Botan::AutoSeeded_RNG);
+
+      if(drbg_seed.size() > 0)
+         rng->add_entropy(drbg_seed.data(), drbg_seed.size());
+      return rng;
+      }
+#endif
+
+#if defined(BOTAN_HAS_HMAC_DRBG)
+   if(rng_type == "drbg")
+      {
+      std::unique_ptr<Botan::MessageAuthenticationCode> mac =
+         Botan::MessageAuthenticationCode::create(BOTAN_AUTO_RNG_HMAC);
+      std::unique_ptr<Botan::Stateful_RNG> rng(new Botan::HMAC_DRBG(std::move(mac)));
+      rng->add_entropy(drbg_seed.data(), drbg_seed.size());
+
+      if(rng->is_seeded() == false)
+         throw CLI_Error("For " + rng->name() + " a seed of at least " +
+                         std::to_string(rng->security_level()/8) +
+                         " bytes must be provided");
+
+      return rng;
+      }
+#endif
+
+   throw CLI_Error_Unsupported("RNG", rng_type);
+   }
+
 class Config_Info final : public Command
    {
    public:
@@ -170,49 +232,24 @@ BOTAN_REGISTER_COMMAND("hash", Hash);
 class RNG final : public Command
    {
    public:
-      RNG() : Command("rng --system --rdrand --entropy *bytes") {}
+      RNG() : Command("rng --system --rdrand --auto --entropy --drbg --drbg-seed= *bytes") {}
 
       void go() override
          {
-         std::unique_ptr<Botan::RNG> rng;
+         std::string type = "auto"; // default
 
-         if(flag_set("system"))
-            {
-#if defined(BOTAN_HAS_SYSTEM_RNG)
-            rng.reset(new Botan::System_RNG);
-#else
-            error_output() << "system_rng disabled in build\n";
-            return;
-#endif
-            }
-         else if(flag_set("rdrand"))
+         for(std::string flag : { "system", "rdrand", "auto", "entropy", "drbg" })
             {
-#if defined(BOTAN_HAS_RDRAND_RNG)
-            rng.reset(new Botan::RDRAND_RNG);
-#else
-            error_output() << "rdrand_rng disabled in build\n";
-            return;
-#endif
-            }
-         else if(flag_set("entropy"))
-            {
-#if defined(BOTAN_HAS_AUTO_SEEDING_RNG)
-            rng.reset(new Botan::AutoSeeded_RNG(Botan::Entropy_Sources::global_sources()));
-#else
-            error_output() << "auto_rng disabled in build\n";
-            return;
-#endif
-            }
-         else
-            {
-#if defined(BOTAN_HAS_AUTO_SEEDING_RNG)
-            rng.reset(new Botan::AutoSeeded_RNG);
-#else
-            error_output() << "auto_rng disabled in build\n";
-            return;
-#endif
+            if(flag_set(flag))
+               {
+               type = flag;
+               break;
+               }
             }
 
+         const std::string drbg_seed = get_arg("drbg-seed");
+         std::unique_ptr<Botan::RNG> rng = cli_make_rng(type, drbg_seed);
+
          for(const std::string& req : get_arg_list("bytes"))
             {
             output() << Botan::hex_encode(rng->random_vec(Botan::to_u32bit(req))) << "\n";