ffi_rng.cpp

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/*
* (C) 2015,2017 Jack Lloyd
* (C) 2021 René Fischer
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/ffi.h>
#include <botan/internal/ffi_util.h>
#include <botan/internal/ffi_rng.h>
#include <botan/system_rng.h>
#include <botan/auto_rng.h>
 
#include <functional>
#include <memory>
 
#if defined(BOTAN_HAS_PROCESSOR_RNG)
#include <botan/processor_rng.h>
#endif
 
extern "C" {
 
using namespace Botan_FFI;
 
int botan_rng_init(botan_rng_t* rng_out, const char* rng_type)
   {
   return ffi_guard_thunk(__func__, [=]() -> int {
   if(rng_out == nullptr)
      return BOTAN_FFI_ERROR_NULL_POINTER;
 
   const std::string rng_type_s(rng_type ? rng_type : "system");
 
   std::unique_ptr<Botan::RandomNumberGenerator> rng;
 
   if(rng_type_s == "system")
      {
      rng = std::make_unique<Botan::System_RNG>();
      }
   else if(rng_type_s == "user" || rng_type_s == "user-threadsafe")
      {
      rng = std::make_unique<Botan::AutoSeeded_RNG>();
      }
   else if(rng_type_s == "null")
      {
      rng = std::make_unique<Botan::Null_RNG>();
      }
#if defined(BOTAN_HAS_PROCESSOR_RNG)
   else if((rng_type_s == "rdrand" || rng_type_s == "hwrng") && Botan::Processor_RNG::available())
      {
      rng = std::make_unique<Botan::Processor_RNG>();
      }
#endif
 
   if(!rng)
      {
      return BOTAN_FFI_ERROR_NOT_IMPLEMENTED;
      }
 
   *rng_out = new botan_rng_struct(std::move(rng));
   return BOTAN_FFI_SUCCESS;
   });
   }
 
int botan_rng_init_custom(botan_rng_t* rng_out, const char* rng_name, void* context,
                          int(* get_cb)(void* context, uint8_t* out, size_t out_len),
                          int(* add_entropy_cb)(void* context, const uint8_t input[], size_t length),
                          void(* destroy_cb)(void* context))
   {
   return ffi_guard_thunk(__func__,[=]() -> int {
   if(rng_out == nullptr)
      return BOTAN_FFI_ERROR_NULL_POINTER;
 
   if(rng_name == nullptr)
      return BOTAN_FFI_ERROR_NULL_POINTER;
 
   if(get_cb == nullptr)
      return BOTAN_FFI_ERROR_NULL_POINTER;
 
   class Custom_RNG : public Botan::RandomNumberGenerator
      {
      public:
         Custom_RNG(std::string_view name, void* context,
                    int(* get_cb)(void* context, uint8_t* out, size_t out_len),
                    int(* add_entropy_cb)(void* context, const uint8_t input[], size_t length),
                    void(* destroy_cb)(void* context)) :
            m_name(name)
            {
            m_context = context;
            m_get_cb = get_cb;
            m_add_entropy_cb = add_entropy_cb;
            m_destroy_cb = destroy_cb;
            }
 
         ~Custom_RNG() override
            {
            if(m_destroy_cb)
               {
               m_destroy_cb(m_context);
               }
            }
 
         Custom_RNG(const Custom_RNG& other) = delete;
         Custom_RNG(Custom_RNG&& other) = delete;
         Custom_RNG& operator=(const Custom_RNG& other) = delete;
         Custom_RNG& operator=(Custom_RNG&& other) = delete;
 
      protected:
         void fill_bytes_with_input(std::span<uint8_t> output, std::span<const uint8_t> input) override
            {
            if(accepts_input() && !input.empty())
               {
               int rc = m_add_entropy_cb(m_context, input.data(), input.size());
               if(rc)
                  {
                  throw Botan::Invalid_State("Failed to add entropy via C callback, rc=" + std::to_string(rc));
                  }
               }
 
            if(!output.empty())
               {
               int rc = m_get_cb(m_context, output.data(), output.size());
               if(rc)
                  {
                  throw Botan::Invalid_State("Failed to get random from C callback, rc=" + std::to_string(rc));
                  }
               }
            }
 
      public:
         bool accepts_input() const override
            {
            return m_add_entropy_cb != nullptr;
            }
 
         std::string name() const override
            {
            return m_name;
            }
 
         void clear() override
            {
            }
 
         bool is_seeded() const override
            {
            return true;
            }
 
      private:
         std::string m_name;
         void* m_context;
         std::function<int(void* context, uint8_t* out, size_t out_len)> m_get_cb;
         std::function<int(void* context, const uint8_t input[], size_t length)> m_add_entropy_cb;
         std::function<void(void* context)> m_destroy_cb;
      };
 
   auto rng = std::make_unique<Custom_RNG>(rng_name, context, get_cb, add_entropy_cb, destroy_cb);
 
   *rng_out = new botan_rng_struct(std::move(rng));
   return BOTAN_FFI_SUCCESS;
   });
   }
 
int botan_rng_destroy(botan_rng_t rng)
   {
   return BOTAN_FFI_CHECKED_DELETE(rng);
   }
 
int botan_rng_get(botan_rng_t rng, uint8_t* out, size_t out_len)
   {
   return BOTAN_FFI_VISIT(rng, [=](auto& r) { r.randomize(out, out_len); });
   }
 
int botan_system_rng_get(uint8_t* out, size_t out_len)
   {
   return ffi_guard_thunk(__func__, [=]() -> int
      {
      Botan::system_rng().randomize(out, out_len);
      return BOTAN_FFI_SUCCESS;
      });
   }
 
int botan_rng_reseed(botan_rng_t rng, size_t bits)
   {
   return BOTAN_FFI_VISIT(rng, [=](auto& r) { r.reseed_from_rng(Botan::system_rng(), bits); });
   }
 
int botan_rng_add_entropy(botan_rng_t rng, const uint8_t* input, size_t len)
   {
   return BOTAN_FFI_VISIT(rng, [=](auto& r) { r.add_entropy(input, len); });
   }
 
int botan_rng_reseed_from_rng(botan_rng_t rng, botan_rng_t source_rng, size_t bits)
   {
   return BOTAN_FFI_VISIT(rng, [=](auto& r) { r.reseed_from_rng(safe_get(source_rng), bits); });
   }
 
}