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 // rdrand.h - written and placed in public domain by Jeffrey Walton and Uri Blumenthal.

 
 /// \file rdrand.h

 /// \brief Classes for RDRAND and RDSEED

 /// \since Crypto++ 5.6.3

 
 #ifndef CRYPTOPP_RDRAND_H
 #define CRYPTOPP_RDRAND_H
 
 #include "cryptlib.h"
 
 // This class file provides both RDRAND and RDSEED. They were added at

 //   Crypto++ 5.6.3. At compile time, it uses CRYPTOPP_BOOL_{X86|X32|X64}

 //   to select an implementation or "throw NotImplemented". At runtime the

 //   constructor will throw RDRAND_Err or RDSEED_Err if a generator is

 //   is not available.

 // The original classes accepted a retry count. Retries were superfluous for

 //   RDRAND, and RDSEED encountered a failure about 1 in 256 bytes depending

 //   on the processor. Retries were removed at Crypto++ 6.0 because

 //   GenerateBlock unconditionally retries and always fulfills the request.

 
 // Throughput varies wildly depending on processor and manufacturer. A Core i5 or

 //   Core i7 RDRAND can generate at over 200 MiB/s. It is below theroetical

 //   maximum, but it takes about 5 instructions to generate, retry and store a

 //   result. A low-end Celeron may perform RDRAND at about 7 MiB/s. RDSEED

 //   performs at about 1/4 to 1/2 the rate of RDRAND. AMD RDRAND performed poorly

 //   during testing with Athlon X4 845. The Bulldozer v4 only performed at 1 MiB/s.

 
 // Microsoft added RDRAND in August 2012, VS2012; RDSEED in October 2013, VS2013.

 // GCC added RDRAND in December 2010, GCC 4.6. LLVM added RDRAND in July 2012,

 // Clang 3.2. Intel added RDRAND in September 2011, ICC 12.1.

 
 NAMESPACE_BEGIN(CryptoPP)
 
 /// \brief Exception thrown when a RDRAND generator encounters

 ///    a generator related error.

 /// \since Crypto++ 5.6.3

 class RDRAND_Err : public Exception
 {
 public:
     RDRAND_Err(const std::string &operation)
         : Exception(OTHER_ERROR, "RDRAND: " + operation + " operation failed") {}
 };
 
 /// \brief Hardware generated random numbers using RDRAND instruction

 /// \sa MaurerRandomnessTest() for random bit generators

 /// \since Crypto++ 5.6.3

 class RDRAND : public RandomNumberGenerator
 {
 public:
     CRYPTOPP_STATIC_CONSTEXPR const char* StaticAlgorithmName() { return "RDRAND"; }
 
     virtual ~RDRAND() {}
 
     /// \brief Construct a RDRAND generator

     /// \details According to DJ of Intel, the Intel RDRAND circuit does not underflow.

     ///   If it did hypothetically underflow, then it would return 0 for the random value.

     ///   AMD's RDRAND implementation appears to provide the same behavior.

      /// \throw RDRAND_Err if the random number generator is not available

     RDRAND();
 
     /// \brief Generate random array of bytes

     /// \param output the byte buffer

     /// \param size the length of the buffer, in bytes

     virtual void GenerateBlock(byte *output, size_t size);
 
     /// \brief Generate and discard n bytes

     /// \param n the number of bytes to generate and discard

     /// \details the RDSEED generator discards words, not bytes. If n is

     ///   not a multiple of a machine word, then it is rounded up to

     ///   that size.

     virtual void DiscardBytes(size_t n);
 
     /// \brief Update RNG state with additional unpredictable values

     /// \param input unused

     /// \param length unused

     /// \details The operation is a nop for this generator.

     virtual void IncorporateEntropy(const byte *input, size_t length)
     {
         // Override to avoid the base class' throw.

         CRYPTOPP_UNUSED(input); CRYPTOPP_UNUSED(length);
     }
 
     std::string AlgorithmProvider() const {
         return "RDRAND";
     }
 };
 
 /// \brief Exception thrown when a RDSEED generator encounters

 ///    a generator related error.

 /// \since Crypto++ 5.6.3

 class RDSEED_Err : public Exception
 {
 public:
     RDSEED_Err(const std::string &operation)
         : Exception(OTHER_ERROR, "RDSEED: " + operation + " operation failed") {}
 };
 
 /// \brief Hardware generated random numbers using RDSEED instruction

 /// \sa MaurerRandomnessTest() for random bit generators

 /// \since Crypto++ 5.6.3

 class RDSEED : public RandomNumberGenerator
 {
 public:
     CRYPTOPP_STATIC_CONSTEXPR const char* StaticAlgorithmName() { return "RDSEED"; }
 
     virtual ~RDSEED() {}
 
     /// \brief Construct a RDSEED generator

     /// \details Empirical testing under a 6th generation i7 (6200U) shows RDSEED fails

     ///   to fulfill requests at about once every for every 256 bytes requested.

     ///   The generator runs about 4 times slower than RDRAND.

      /// \throw RDSEED_Err if the random number generator is not available

     RDSEED();
 
     /// \brief Generate random array of bytes

     /// \param output the byte buffer

     /// \param size the length of the buffer, in bytes

     virtual void GenerateBlock(byte *output, size_t size);
 
     /// \brief Generate and discard n bytes

     /// \param n the number of bytes to generate and discard

     /// \details the RDSEED generator discards words, not bytes. If n is

     ///   not a multiple of a machine word, then it is rounded up to

     ///   that size.

     virtual void DiscardBytes(size_t n);
 
     /// \brief Update RNG state with additional unpredictable values

     /// \param input unused

     /// \param length unused

     /// \details The operation is a nop for this generator.

     virtual void IncorporateEntropy(const byte *input, size_t length)
     {
         // Override to avoid the base class' throw.

         CRYPTOPP_UNUSED(input); CRYPTOPP_UNUSED(length);
     }
 
     std::string AlgorithmProvider() const {
         return "RDSEED";
     }
 };
 
 NAMESPACE_END
 
 #endif // CRYPTOPP_RDRAND_H

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