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/auto_rng.h>
#include <botan/system_rng.h>
#include <botan/internal/ffi_rng.h>
#include <botan/internal/ffi_util.h>
 
#include <functional>
#include <memory>
 
#if defined(BOTAN_HAS_PROCESSOR_RNG)
   #include <botan/processor_rng.h>
#endif
 
#if defined(BOTAN_HAS_JITTER_RNG)
   #include <botan/jitter_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 defined(BOTAN_HAS_JITTER_RNG)
      else if(rng_type_s == "jitter") {
         rng = std::make_unique<Botan::Jitter_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); });
}
}