SecureRandom.h

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/*
* Copyright 2010-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
*  http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file is distributed
* on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
* express or implied. See the License for the specific language governing
* permissions and limitations under the License.
*/
#pragma once
#include <type_traits>

namespace Aws
{
    namespace Utils
    {
        namespace Crypto
        {
            class SecureRandomBytes
            {
            public:
                SecureRandomBytes() : m_failure(false)
                {
                }

                virtual ~SecureRandomBytes() = default;

                virtual void GetBytes(unsigned char* buffer, size_t bufferSize) = 0;

                operator bool() const { return !m_failure; }

            protected:
                bool m_failure;
            };

            template <typename DataType = uint64_t>
            class SecureRandom
            {
            public:
                SecureRandom(const std::shared_ptr<SecureRandomBytes>& entropySource) : m_entropy(entropySource)
                    { static_assert(std::is_unsigned<DataType>::value, "Type DataType must be integral"); }

                virtual ~SecureRandom() = default;

                virtual void Reset() {}

                virtual DataType operator()()
                {
                    DataType value(0);
                    unsigned char buffer[sizeof(DataType)];
                    m_entropy->GetBytes(buffer, sizeof(DataType));

                    assert(*m_entropy);
                    if(*m_entropy)
                    {
                        for (size_t i = 0; i < sizeof(DataType); ++i)
                        {
                             value <<= 8;
                             value |= buffer[i];

                        }
                    }

                    return value;
                }

                operator bool() const { return *m_entropy; }

            private:
                std::shared_ptr<SecureRandomBytes> m_entropy;
            };           

            class SecureRandomFactory
            {
            public:
                virtual std::shared_ptr<SecureRandomBytes> CreateImplementation() const = 0;

                virtual void InitStaticState() {}

                virtual void CleanupStaticState() {}
            };
        }
    }
}