/*

* System RNG

* (C) 2014,2015,2017,2018 Jack Lloyd

* (C) 2021 Tom Crowley

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#include <botan/system_rng.h>

#if defined(BOTAN_TARGET_OS_HAS_RTLGENRANDOM)

  #include <botan/internal/dyn_load.h>

  #define NOMINMAX 1

  #define _WINSOCKAPI_ // stop windows.h including winsock.h

  #include <windows.h>

#elif defined(BOTAN_TARGET_OS_HAS_CRYPTO_NG)

  #include <bcrypt.h>

#elif defined(BOTAN_TARGET_OS_HAS_ARC4RANDOM)

  #include <stdlib.h>

#elif defined(BOTAN_TARGET_OS_HAS_GETRANDOM)

  #include <sys/random.h>

  #include <errno.h>

#elif defined(BOTAN_TARGET_OS_HAS_DEV_RANDOM)

  #include <sys/types.h>

  #include <sys/stat.h>

  #include <fcntl.h>

  #include <unistd.h>

  #include <errno.h>

#endif

namespace Botan {

namespace {

#if defined(BOTAN_TARGET_OS_HAS_RTLGENRANDOM)

class System_RNG_Impl final : public RandomNumberGenerator

   {

   public:

      System_RNG_Impl() : m_advapi("advapi32.dll")

         {

         // This throws if the function is not found

         m_rtlgenrandom = m_advapi.resolve<RtlGenRandom_fptr>("SystemFunction036");

         }

      void randomize(uint8_t buf[], size_t len) override

         {

         const size_t limit = std::numeric_limits<ULONG>::max();

         uint8_t* pData = buf;

         size_t bytesLeft = len;

         while (bytesLeft > 0)

            {

            const ULONG blockSize = static_cast<ULONG>(std::min(bytesLeft, limit));

            const bool success = m_rtlgenrandom(pData, blockSize) == TRUE;

            if (!success)

               {

               throw System_Error("RtlGenRandom failed");

               }

            BOTAN_ASSERT(bytesLeft >= blockSize, "Block is oversized");

            bytesLeft -= blockSize;

            pData += blockSize;

            }

         }

      void add_entropy(const uint8_t[], size_t) override { /* ignored */ }

      bool is_seeded() const override { return true; }

      bool accepts_input() const override { return false; }

      void clear() override { /* not possible */ }

      std::string name() const override { return "RtlGenRandom"; }

   private:

      using RtlGenRandom_fptr = BOOLEAN (NTAPI *)(PVOID, ULONG);

      Dynamically_Loaded_Library m_advapi;

      RtlGenRandom_fptr m_rtlgenrandom;

   };

#elif defined(BOTAN_TARGET_OS_HAS_CRYPTO_NG)

class System_RNG_Impl final : public RandomNumberGenerator

   {

   public:

      System_RNG_Impl()

         {

         NTSTATUS ret = ::BCryptOpenAlgorithmProvider(&m_prov,

                                                      BCRYPT_RNG_ALGORITHM,

                                                      MS_PRIMITIVE_PROVIDER, 0);

         if(ret != STATUS_SUCCESS)

            throw System_Error("System_RNG failed to acquire crypto provider", ret);

         }

      ~System_RNG_Impl()

         {

         ::BCryptCloseAlgorithmProvider(m_prov, 0);

         }

      void randomize(uint8_t buf[], size_t len) override

         {

         const size_t limit = std::numeric_limits<ULONG>::max();

         uint8_t* pData = buf;

         size_t bytesLeft = len;

         while (bytesLeft > 0)

            {

            const ULONG blockSize = static_cast<ULONG>(std::min(bytesLeft, limit));

            const NTSTATUS ret = BCryptGenRandom(m_prov, static_cast<PUCHAR>(pData), blockSize, 0);

            if (ret != STATUS_SUCCESS)

               {

               throw System_Error("System_RNG call to BCryptGenRandom failed", ret);

               }

            BOTAN_ASSERT(bytesLeft >= blockSize, "Block is oversized");

            bytesLeft -= blockSize;

            pData += blockSize;

            }

         }

      void add_entropy(const uint8_t in[], size_t length) override

         {

         /*

         There is a flag BCRYPT_RNG_USE_ENTROPY_IN_BUFFER to provide

         entropy inputs, but it is ignored in Windows 8 and later.

         */

         }

      bool is_seeded() const override { return true; }

      bool accepts_input() const override { return false; }

      void clear() override { /* not possible */ }

      std::string name() const override { return "crypto_ng"; }

   private:

      BCRYPT_ALG_HANDLE m_prov;

   };

#elif defined(BOTAN_TARGET_OS_HAS_ARC4RANDOM)

class System_RNG_Impl final : public RandomNumberGenerator

   {

   public:

      // No constructor or destructor needed as no userland state maintained

      void randomize(uint8_t buf[], size_t len) override

         {

         // macOS 10.15 arc4random crashes if called with buf == nullptr && len == 0

         if(len > 0)

            {

            ::arc4random_buf(buf, len);

            }

         }

      bool accepts_input() const override { return false; }

      void add_entropy(const uint8_t[], size_t) override { /* ignored */ }

      bool is_seeded() const override { return true; }

      void clear() override { /* not possible */ }

      std::string name() const override { return "arc4random"; }

   };

#elif defined(BOTAN_TARGET_OS_HAS_GETRANDOM)

class System_RNG_Impl final : public RandomNumberGenerator

   {

   public:

      // No constructor or destructor needed as no userland state maintained

      void randomize(uint8_t buf[], size_t len) override

         {

         const unsigned int flags = 0;

         while(len > 0)

            {

            const ssize_t got = ::getrandom(buf, len, flags);

            if(got < 0)

               {

               if(errno == EINTR)

                  continue;

               throw System_Error("System_RNG getrandom failed", errno);

               }

            buf += got;

            len -= got;

            }

         }

      bool accepts_input() const override { return false; }

      void add_entropy(const uint8_t[], size_t) override { /* ignored */ }

      bool is_seeded() const override { return true; }

      void clear() override { /* not possible */ }

      std::string name() const override { return "getrandom"; }

   };

#elif defined(BOTAN_TARGET_OS_HAS_DEV_RANDOM)

// Read a random device

class System_RNG_Impl final : public RandomNumberGenerator

   {

   public:

      System_RNG_Impl()

         {

#ifndef O_NOCTTY

#define O_NOCTTY 0

#endif

         /*

         * First open /dev/random and read one byte. On old Linux kernels

         * this blocks the RNG until we have been actually seeded.

         */

         m_fd = ::open("/dev/random", O_RDONLY | O_NOCTTY);

         if(m_fd < 0)

            throw System_Error("System_RNG failed to open RNG device", errno);

         uint8_t b;

         const size_t got = ::read(m_fd, &b, 1);

         ::close(m_fd);

         if(got != 1)

            throw System_Error("System_RNG failed to read blocking RNG device");

         m_fd = ::open("/dev/urandom", O_RDWR | O_NOCTTY);

         if(m_fd >= 0)

            {

            m_writable = true;

            }

         else

            {

            /*

            Cannot open in read-write mode. Fall back to read-only,

            calls to add_entropy will fail, but randomize will work

            */

            m_fd = ::open("/dev/urandom", O_RDONLY | O_NOCTTY);

            m_writable = false;

            }

         if(m_fd < 0)

            throw System_Error("System_RNG failed to open RNG device", errno);

         }

      ~System_RNG_Impl()

         {

         ::close(m_fd);

         m_fd = -1;

         }

      void randomize(uint8_t buf[], size_t len) override;

      void add_entropy(const uint8_t in[], size_t length) override;

      bool is_seeded() const override { return true; }

      bool accepts_input() const override { return m_writable; }

      void clear() override { /* not possible */ }

      std::string name() const override { return "urandom"; }

   private:

      int m_fd;

      bool m_writable;

   };

void System_RNG_Impl::randomize(uint8_t buf[], size_t len)

   {

   while(len)

      {

      ssize_t got = ::read(m_fd, buf, len);

      if(got < 0)

         {

         if(errno == EINTR)

            continue;

         throw System_Error("System_RNG read failed", errno);

         }

      if(got == 0)

         throw System_Error("System_RNG EOF on device"); // ?!?

      buf += got;

      len -= got;

      }

   }

void System_RNG_Impl::add_entropy(const uint8_t input[], size_t len)

   {

   if(!m_writable)

      return;

   while(len)

      {

      ssize_t got = ::write(m_fd, input, len);

      if(got < 0)

         {

         if(errno == EINTR)

            continue;

         /*

         * This is seen on OS X CI, despite the fact that the man page

         * for macOS urandom explicitly states that writing to it is

         * supported, and write(2) does not document EPERM at all.

         * But in any case EPERM seems indicative of a policy decision

         * by the OS or sysadmin that additional entropy is not wanted

         * in the system pool, so we accept that and return here,

         * since there is no corrective action possible.

         *

         * In Linux EBADF or EPERM is returned if m_fd is not opened for

         * writing.

         */

         if(errno == EPERM || errno == EBADF)

            return;

         // maybe just ignore any failure here and return?

         throw System_Error("System_RNG write failed", errno);

         }

      input += got;

      len -= got;

      }

   }

#endif

}

RandomNumberGenerator& system_rng()

   {

   static System_RNG_Impl g_system_rng;

   return g_system_rng;

   }

}