secblock.h

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// secblock.h - originally written and placed in the public domain by Wei Dai
 
/// \file secblock.h
/// \brief Classes and functions for secure memory allocations.
 
#ifndef CRYPTOPP_SECBLOCK_H
#define CRYPTOPP_SECBLOCK_H
 
#include "config.h"
#include "allocate.h"
#include "misc.h"
#include "stdcpp.h"
 
#if CRYPTOPP_MSC_VERSION
# pragma warning(push)
# pragma warning(disable: 4231 4275 4700)
# if (CRYPTOPP_MSC_VERSION >= 1400)
#  pragma warning(disable: 6011 6386 28193)
# endif
#endif
 
NAMESPACE_BEGIN(CryptoPP)
 
// ************** secure memory allocation ***************
 
/// \brief Base class for all allocators used by SecBlock
/// \tparam T the class or type
template<class T>
class AllocatorBase
{
public:
    typedef T value_type;
    typedef size_t size_type;
    typedef std::ptrdiff_t difference_type;
    typedef T * pointer;
    typedef const T * const_pointer;
    typedef T & reference;
    typedef const T & const_reference;
 
    pointer address(reference r) const {return (&r);}
    const_pointer address(const_reference r) const {return (&r); }
    void construct(pointer p, const T& val) {new (p) T(val);}
    void destroy(pointer p) {CRYPTOPP_UNUSED(p); p->~T();}
 
    /// \brief Returns the maximum number of elements the allocator can provide
    /// \details <tt>ELEMS_MAX</tt> is the maximum number of elements the
    ///  <tt>Allocator</tt> can provide. The value of <tt>ELEMS_MAX</tt> is
    ///  <tt>SIZE_MAX/sizeof(T)</tt>. <tt>std::numeric_limits</tt> was avoided
    ///  due to lack of <tt>constexpr</tt>-ness in C++03 and below.
    /// \note In C++03 and below <tt>ELEMS_MAX</tt> is a static data member of type
    ///  <tt>size_type</tt>. In C++11 and above <tt>ELEMS_MAX</tt> is an <tt>enum</tt>
    ///  inheriting from <tt>size_type</tt>. In both cases <tt>ELEMS_MAX</tt> can be
    ///  used before objects are fully constructed, and it does not suffer the
    ///  limitations of class methods like <tt>max_size</tt>.
    /// \sa <A HREF="http://github.com/weidai11/cryptopp/issues/346">Issue 346/CVE-2016-9939</A>
    /// \since Crypto++ 6.0
#if defined(CRYPTOPP_DOXYGEN_PROCESSING)
    static const size_type ELEMS_MAX = ...;
#elif defined(_MSC_VER) && (_MSC_VER <= 1400)
    static const size_type ELEMS_MAX = (~(size_type)0)/sizeof(T);
#elif defined(CRYPTOPP_CXX11_STRONG_ENUM)
    enum : size_type {ELEMS_MAX = SIZE_MAX/sizeof(T)};
#else
    static const size_type ELEMS_MAX = SIZE_MAX/sizeof(T);
#endif
 
    /// \brief Returns the maximum number of elements the allocator can provide
    /// \return the maximum number of elements the allocator can provide
    /// \details Internally, preprocessor macros are used rather than std::numeric_limits
    ///  because the latter is not a constexpr. Some compilers, like Clang, do not
    ///  optimize it well under all circumstances. Compilers like GCC, ICC and MSVC appear
    ///  to optimize it well in either form.
    CRYPTOPP_CONSTEXPR size_type max_size() const {return ELEMS_MAX;}
 
#if defined(__SUNPRO_CC)
    // https://github.com/weidai11/cryptopp/issues/770
    // and https://stackoverflow.com/q/53999461/608639
    CRYPTOPP_CONSTEXPR size_type max_size(size_type n) const {return SIZE_MAX/n;}
#endif
 
#if defined(CRYPTOPP_CXX11_VARIADIC_TEMPLATES) || defined(CRYPTOPP_DOXYGEN_PROCESSING)
 
    /// \brief Constructs a new V using variadic arguments
    /// \tparam V the type to be forwarded
    /// \tparam Args the arguments to be forwarded
    /// \param ptr pointer to type V
    /// \param args variadic arguments
    /// \details This is a C++11 feature. It is available when CRYPTOPP_CXX11_VARIADIC_TEMPLATES
    ///  is defined. The define is controlled by compiler versions detected in config.h.
    template<typename V, typename... Args>
    void construct(V* ptr, Args&&... args) {::new ((void*)ptr) V(std::forward<Args>(args)...);}
 
    /// \brief Destroys an V constructed with variadic arguments
    /// \tparam V the type to be forwarded
    /// \details This is a C++11 feature. It is available when CRYPTOPP_CXX11_VARIADIC_TEMPLATES
    ///  is defined. The define is controlled by compiler versions detected in config.h.
    template<typename V>
    void destroy(V* ptr) {if (ptr) ptr->~V();}
 
#endif
 
protected:
 
    /// \brief Verifies the allocator can satisfy a request based on size
    /// \param size the size of the allocation, in elements
    /// \throw InvalidArgument
    /// \details CheckSize verifies the number of elements requested is valid.
    /// \details If size is greater than max_size(), then InvalidArgument is thrown.
    ///  The library throws InvalidArgument if the size is too large to satisfy.
    /// \details Internally, preprocessor macros are used rather than std::numeric_limits
    ///  because the latter is not a constexpr. Some compilers, like Clang, do not
    ///  optimize it well under all circumstances. Compilers like GCC, ICC and MSVC appear
    ///  to optimize it well in either form.
    /// \details The <tt>sizeof(T) != 1</tt> in the condition attempts to help the
    ///  compiler optimize the check for byte types. Coverity findings for
    ///  CONSTANT_EXPRESSION_RESULT were generated without it. For byte types,
    ///  size never exceeded ELEMS_MAX but the code was not removed.
    /// \note size is the count of elements, and not the number of bytes
    static void CheckSize(size_t size)
    {
        // Squash MSC C4100 warning for size. Also see commit 42b7c4ea5673.
        CRYPTOPP_UNUSED(size);
        // C++ throws std::bad_alloc (C++03) or std::bad_array_new_length (C++11) here.
        if (sizeof(T) != 1 && size > ELEMS_MAX)
            throw InvalidArgument("AllocatorBase: requested size would cause integer overflow");
    }
};
 
#define CRYPTOPP_INHERIT_ALLOCATOR_TYPES(T_type)    \
    typedef typename AllocatorBase<T_type>::value_type value_type;\
    typedef typename AllocatorBase<T_type>::size_type size_type;\
    typedef typename AllocatorBase<T_type>::difference_type difference_type;\
    typedef typename AllocatorBase<T_type>::pointer pointer;\
    typedef typename AllocatorBase<T_type>::const_pointer const_pointer;\
    typedef typename AllocatorBase<T_type>::reference reference;\
    typedef typename AllocatorBase<T_type>::const_reference const_reference;
 
/// \brief Reallocation function
/// \tparam T the class or type
/// \tparam A the class or type's allocator
/// \param alloc the allocator
/// \param oldPtr the previous allocation
/// \param oldSize the size of the previous allocation
/// \param newSize the new, requested size
/// \param preserve flag that indicates if the old allocation should be preserved
/// \note oldSize and newSize are the count of elements, and not the
///  number of bytes.
template <class T, class A>
typename A::pointer StandardReallocate(A& alloc, T *oldPtr, typename A::size_type oldSize, typename A::size_type newSize, bool preserve)
{
    // Avoid assert on pointer in reallocate. SecBlock regularly uses NULL
    // pointers rather returning non-NULL 0-sized pointers.
    if (oldSize == newSize)
        return oldPtr;
 
    if (preserve)
    {
        typename A::pointer newPtr = alloc.allocate(newSize, NULLPTR);
        const typename A::size_type copySize = STDMIN(oldSize, newSize) * sizeof(T);
 
        if (oldPtr && newPtr)
            memcpy_s(newPtr, copySize, oldPtr, copySize);
 
        if (oldPtr)
            alloc.deallocate(oldPtr, oldSize);
 
        return newPtr;
    }
    else
    {
        if (oldPtr)
            alloc.deallocate(oldPtr, oldSize);
 
        return alloc.allocate(newSize, NULLPTR);
    }
}
 
/// \brief Allocates a block of memory with cleanup
/// \tparam T class or type
/// \tparam T_Align16 boolean that determines whether allocations should be aligned on a 16-byte boundary
/// \details If T_Align16 is true, then AllocatorWithCleanup calls AlignedAllocate()
///  for memory allocations. If T_Align16 is false, then AllocatorWithCleanup() calls
///  UnalignedAllocate() for memory allocations.
/// \details Template parameter T_Align16 is effectively controlled by cryptlib.h and mirrors
///  CRYPTOPP_BOOL_ALIGN16. CRYPTOPP_BOOL_ALIGN16 is often used as the template parameter.
template <class T, bool T_Align16 = false>
class AllocatorWithCleanup : public AllocatorBase<T>
{
public:
    CRYPTOPP_INHERIT_ALLOCATOR_TYPES(T)
 
    /// \brief Allocates a block of memory
    /// \param ptr the size of the allocation
    /// \param size the size of the allocation, in elements
    /// \return a memory block
    /// \throw InvalidArgument
    /// \details allocate() first checks the size of the request. If it is non-0
    ///  and less than max_size(), then an attempt is made to fulfill the request
    ///  using either AlignedAllocate() or UnalignedAllocate(). AlignedAllocate() is
    ///  used if T_Align16 is true. UnalignedAllocate() used if T_Align16 is false.
    /// \details This is the C++ *Placement New* operator. ptr is not used, and the
    ///  function asserts in Debug builds if ptr is non-NULL.
    /// \sa CallNewHandler() for the methods used to recover from a failed
    ///  allocation attempt.
    /// \note size is the count of elements, and not the number of bytes
    pointer allocate(size_type size, const void *ptr = NULLPTR)
    {
        CRYPTOPP_UNUSED(ptr); CRYPTOPP_ASSERT(ptr == NULLPTR);
        this->CheckSize(size);
        if (size == 0)
            return NULLPTR;
 
#if CRYPTOPP_BOOL_ALIGN16
        if (T_Align16)
            return reinterpret_cast<pointer>(AlignedAllocate(size*sizeof(T)));
#endif
 
        return reinterpret_cast<pointer>(UnalignedAllocate(size*sizeof(T)));
    }
 
    /// \brief Deallocates a block of memory
    /// \param ptr the pointer for the allocation
    /// \param size the size of the allocation, in elements
    /// \details Internally, SecureWipeArray() is called before deallocating the
    ///  memory. Once the memory block is wiped or zeroized, AlignedDeallocate()
    ///  or UnalignedDeallocate() is called.
    /// \details AlignedDeallocate() is used if T_Align16 is true.
    ///  UnalignedDeallocate() used if T_Align16 is false.
    void deallocate(void *ptr, size_type size)
    {
        // Avoid assert on pointer in deallocate. SecBlock regularly uses NULL
        // pointers rather returning non-NULL 0-sized pointers.
        if (ptr)
        {
            SecureWipeArray(reinterpret_cast<pointer>(ptr), size);
 
#if CRYPTOPP_BOOL_ALIGN16
            if (T_Align16)
                return AlignedDeallocate(ptr);
#endif
 
            UnalignedDeallocate(ptr);
        }
    }
 
    /// \brief Reallocates a block of memory
    /// \param oldPtr the previous allocation
    /// \param oldSize the size of the previous allocation
    /// \param newSize the new, requested size
    /// \param preserve flag that indicates if the old allocation should be preserved
    /// \return pointer to the new memory block
    /// \details Internally, reallocate() calls StandardReallocate().
    /// \details If preserve is true, then index 0 is used to begin copying the
    ///  old memory block to the new one. If the block grows, then the old array
    ///  is copied in its entirety. If the block shrinks, then only newSize
    ///  elements are copied from the old block to the new one.
    /// \note oldSize and newSize are the count of elements, and not the
    ///  number of bytes.
    pointer reallocate(T *oldPtr, size_type oldSize, size_type newSize, bool preserve)
    {
        CRYPTOPP_ASSERT((oldPtr && oldSize) || !(oldPtr || oldSize));
        return StandardReallocate(*this, oldPtr, oldSize, newSize, preserve);
    }
 
    /// \brief Template class member Rebind
    /// \tparam V bound class or type
    /// \details Rebind allows a container class to allocate a different type of object
    ///  to store elements. For example, a std::list will allocate std::list_node to
    ///  store elements in the list.
    /// \details VS.NET STL enforces the policy of "All STL-compliant allocators
    ///  have to provide a template class member called rebind".
    template <class V> struct rebind { typedef AllocatorWithCleanup<V, T_Align16> other; };
#if _MSC_VER >= 1500
    AllocatorWithCleanup() {}
    template <class V, bool A> AllocatorWithCleanup(const AllocatorWithCleanup<V, A> &) {}
#endif
};
 
CRYPTOPP_DLL_TEMPLATE_CLASS AllocatorWithCleanup<byte>;
CRYPTOPP_DLL_TEMPLATE_CLASS AllocatorWithCleanup<word16>;
CRYPTOPP_DLL_TEMPLATE_CLASS AllocatorWithCleanup<word32>;
CRYPTOPP_DLL_TEMPLATE_CLASS AllocatorWithCleanup<word64>;
#if defined(CRYPTOPP_WORD128_AVAILABLE)
CRYPTOPP_DLL_TEMPLATE_CLASS AllocatorWithCleanup<word128, true>; // for Integer
#endif
#if CRYPTOPP_BOOL_X86
CRYPTOPP_DLL_TEMPLATE_CLASS AllocatorWithCleanup<word, true>;    // for Integer
#endif
 
/// \brief NULL allocator
/// \tparam T class or type
/// \details A NullAllocator is useful for fixed-size, stack based allocations
///  (i.e., static arrays used by FixedSizeAllocatorWithCleanup).
/// \details A NullAllocator always returns 0 for max_size(), and always returns
///  NULL for allocation requests. Though the allocator does not allocate at
///  runtime, it does perform a secure wipe or zeroization during cleanup.
template <class T>
class NullAllocator : public AllocatorBase<T>
{
public:
    //LCOV_EXCL_START
    CRYPTOPP_INHERIT_ALLOCATOR_TYPES(T)
 
    // TODO: should this return NULL or throw bad_alloc? Non-Windows C++ standard
    // libraries always throw. And late mode Windows throws. Early model Windows
    // (circa VC++ 6.0) returned NULL.
    pointer allocate(size_type n, const void* unused = NULLPTR)
    {
        CRYPTOPP_UNUSED(n); CRYPTOPP_UNUSED(unused);
        CRYPTOPP_ASSERT(false); return NULLPTR;
    }
 
    void deallocate(void *p, size_type n)
    {
        CRYPTOPP_UNUSED(p); CRYPTOPP_UNUSED(n);
        CRYPTOPP_ASSERT(false);
    }
 
    CRYPTOPP_CONSTEXPR size_type max_size() const {return 0;}
    //LCOV_EXCL_STOP
};
 
/// \brief Static secure memory block with cleanup
/// \tparam T class or type
/// \tparam S fixed-size of the stack-based memory block, in elements
/// \tparam T_Align16 boolean that determines whether allocations should
///  be aligned on a 16-byte boundary
/// \details FixedSizeAllocatorWithCleanup provides a fixed-size, stack-
///  based allocation at compile time. The class can grow its memory
///  block at runtime if a suitable allocator is available. If size
///  grows beyond S and a suitable allocator is available, then the
///  statically allocated array is obsoleted.
/// \note This allocator can't be used with standard collections because
///  they require that all objects of the same allocator type are equivalent.
template <class T, size_t S, class A = NullAllocator<T>, bool T_Align16 = false>
class FixedSizeAllocatorWithCleanup : public AllocatorBase<T>
{
    // The body of FixedSizeAllocatorWithCleanup is provided in the two
    // partial specializations that follow. The two specializations
    // pivot on the boolean template parameter T_Align16.
};
 
/// \brief Static secure memory block with cleanup
/// \tparam T class or type
/// \tparam S fixed-size of the stack-based memory block, in elements
/// \details FixedSizeAllocatorWithCleanup provides a fixed-size, stack-
///  based allocation at compile time. The class can grow its memory
///  block at runtime if a suitable allocator is available. If size
///  grows beyond S and a suitable allocator is available, then the
///  statically allocated array is obsoleted.
/// \note This allocator can't be used with standard collections because
///  they require that all objects of the same allocator type are equivalent.
template <class T, size_t S, class A>
class FixedSizeAllocatorWithCleanup<T, S, A, true> : public AllocatorBase<T>
{
public:
    CRYPTOPP_INHERIT_ALLOCATOR_TYPES(T)
 
    /// \brief Constructs a FixedSizeAllocatorWithCleanup
    FixedSizeAllocatorWithCleanup() : m_allocated(false) {}
 
    /// \brief Allocates a block of memory
    /// \param size the count elements in the memory block
    /// \details FixedSizeAllocatorWithCleanup provides a fixed-size, stack-based
    ///  allocation at compile time. If size is less than or equal to
    ///  <tt>S</tt>, then a pointer to the static array is returned.
    /// \details The class can grow its memory block at runtime if a suitable
    ///  allocator is available. If size grows beyond S and a suitable
    ///  allocator is available, then the statically allocated array is
    ///  obsoleted. If a suitable allocator is not available, as with a
    ///  NullAllocator, then the function returns NULL and a runtime error
    ///  eventually occurs.
    /// \sa reallocate(), SecBlockWithHint
    pointer allocate(size_type size)
    {
        CRYPTOPP_ASSERT(IsAlignedOn(m_array, 8));
 
        if (size <= S && !m_allocated)
        {
            m_allocated = true;
            return GetAlignedArray();
        }
        else
            return m_fallbackAllocator.allocate(size);
    }
 
    /// \brief Allocates a block of memory
    /// \param size the count elements in the memory block
    /// \param hint an unused hint
    /// \details FixedSizeAllocatorWithCleanup provides a fixed-size, stack-
    ///  based allocation at compile time. If size is less than or equal to
    ///  S, then a pointer to the static array is returned.
    /// \details The class can grow its memory block at runtime if a suitable
    ///  allocator is available. If size grows beyond S and a suitable
    ///  allocator is available, then the statically allocated array is
    ///  obsoleted. If a suitable allocator is not available, as with a
    ///  NullAllocator, then the function returns NULL and a runtime error
    ///  eventually occurs.
    /// \sa reallocate(), SecBlockWithHint
    pointer allocate(size_type size, const void *hint)
    {
        CRYPTOPP_ASSERT(IsAlignedOn(m_array, 8));
 
        if (size <= S && !m_allocated)
        {
            m_allocated = true;
            return GetAlignedArray();
        }
        else
            return m_fallbackAllocator.allocate(size, hint);
    }
 
    /// \brief Deallocates a block of memory
    /// \param ptr a pointer to the memory block to deallocate
    /// \param size the count elements in the memory block
    /// \details The memory block is wiped or zeroized before deallocation.
    ///  If the statically allocated memory block is active, then no
    ///  additional actions are taken after the wipe.
    /// \details If a dynamic memory block is active, then the pointer and
    ///  size are passed to the allocator for deallocation.
    void deallocate(void *ptr, size_type size)
    {
        // Avoid assert on pointer in deallocate. SecBlock regularly uses NULL
        // pointers rather returning non-NULL 0-sized pointers.
        if (ptr == GetAlignedArray())
        {
            // If the m_allocated assert fires then the bit twiddling for
            // GetAlignedArray() is probably incorrect for the platform.
            // Be sure to check CRYPTOPP_ALIGN_DATA(8). The platform may
            // not have a way to declaratively align data to 8.
            CRYPTOPP_ASSERT(size <= S);
            CRYPTOPP_ASSERT(m_allocated);
            m_allocated = false;
            SecureWipeArray(reinterpret_cast<pointer>(ptr), size);
        }
        else
        {
            if (ptr)
                m_fallbackAllocator.deallocate(ptr, size);
        }
    }
 
    /// \brief Reallocates a block of memory
    /// \param oldPtr the previous allocation
    /// \param oldSize the size of the previous allocation
    /// \param newSize the new, requested size
    /// \param preserve flag that indicates if the old allocation should
    ///  be preserved
    /// \return pointer to the new memory block
    /// \details FixedSizeAllocatorWithCleanup provides a fixed-size, stack-
    ///  based allocation at compile time. If size is less than or equal to
    ///  S, then a pointer to the static array is returned.
    /// \details The class can grow its memory block at runtime if a suitable
    ///  allocator is available. If size grows beyond S and a suitable
    ///  allocator is available, then the statically allocated array is
    ///  obsoleted. If a suitable allocator is not available, as with a
    ///  NullAllocator, then the function returns NULL and a runtime error
    ///  eventually occurs.
    /// \note size is the count of elements, and not the number of bytes.
    /// \sa reallocate(), SecBlockWithHint
    pointer reallocate(pointer oldPtr, size_type oldSize, size_type newSize, bool preserve)
    {
        if (oldPtr == GetAlignedArray() && newSize <= S)
        {
            CRYPTOPP_ASSERT(oldSize <= S);
            if (oldSize > newSize)
                SecureWipeArray(oldPtr+newSize, oldSize-newSize);
            return oldPtr;
        }
 
        pointer newPtr = allocate(newSize, NULLPTR);
        if (preserve && newSize)
        {
            const size_type copySize = STDMIN(oldSize, newSize);
            if (newPtr && oldPtr)  // GCC analyzer warning
                memcpy_s(newPtr, sizeof(T)*newSize, oldPtr, sizeof(T)*copySize);
        }
        deallocate(oldPtr, oldSize);
        return newPtr;
    }
 
    CRYPTOPP_CONSTEXPR size_type max_size() const
    {
        return STDMAX(m_fallbackAllocator.max_size(), S);
    }
 
private:
 
#if CRYPTOPP_BOOL_ALIGN16
 
    // There be demons here... We cannot use CRYPTOPP_ALIGN_DATA(16)
    // because linkers on 32-bit machines and some 64-bit machines
    // align the stack to 8-bytes or less, and not 16-bytes as
    // requested. We can only count on a smaller alignment. All
    // toolchains tested appear to honor CRYPTOPP_ALIGN_DATA(8). Also
    // see http://stackoverflow.com/a/1468656/608639.
    //
    // The 16-byte alignment is achieved by padding the requested
    // size with extra elements so we have at least 8-bytes of slack
    // to work with. Then the array pointer is moved to achieve a
    // 16-byte alignment.
    //
    // The additional 8-bytes introduces a small secondary issue.
    // The secondary issue is, a large T results in 0 = 8/sizeof(T).
    // The library is OK but users may hit it. So we need to guard
    // for a large T, and that is what the enum and PAD achieves.
    T* GetAlignedArray() {
 
        // m_array is aligned on 8 byte boundaries due to
        // CRYPTOPP_ALIGN_DATA(8). If m_array%16 is 0, then the buffer
        // is 16-byte aligned and nothing needs to be done. if
        // m_array%16 is 8, then the buffer is not 16-byte aligned and
        // we need to add 8. 8 has that nice symmetric property.
        //
        // If we needed to use CRYPTOPP_ALIGN_DATA(4) due to toolchain
        // limitations, then the calculation would be slightly more
        // costly: ptr = m_array + (16 - (m_array % 16)) % 16;
        CRYPTOPP_ASSERT(IsAlignedOn(m_array, 8));
        int off = reinterpret_cast<uintptr_t>(m_array) % 16;
        byte* ptr = reinterpret_cast<byte*>(m_array) + off;
 
        // Verify the 16-byte alignment. This is the point
        // of these extra gyrations.
        CRYPTOPP_ASSERT(IsAlignedOn(ptr, 16));
        // Verify the lower bound. This is Issue 982/988.
        CRYPTOPP_ASSERT(
            reinterpret_cast<uintptr_t>(ptr) >=
              reinterpret_cast<uintptr_t>(m_array)
        );
        // Verify the upper bound. Allocated array with
        // pad is large enough.
        CRYPTOPP_ASSERT(
            reinterpret_cast<uintptr_t>(ptr+S*sizeof(T)) <=
              reinterpret_cast<uintptr_t>(m_array+(S+PAD))
        );
 
        // void* to silence Clang warnings
        return reinterpret_cast<T*>(
          static_cast<void*>(ptr)
        );
    }
 
    // PAD is elements, not bytes, and rounded up to ensure no overflow.
    enum { Q = sizeof(T), PAD = (Q >= 8) ? 1 : (Q >= 4) ? 2 : (Q >= 2) ? 4 : 8 };
    // enum { Q = sizeof(T), PAD = (Q >= 16) ? 1 : (Q >= 8) ? 2 : (Q >= 4) ? 4 : (Q >= 2) ? 8 : 16 };
    CRYPTOPP_ALIGN_DATA(8) T m_array[S+PAD];
 
#else
 
    // CRYPTOPP_BOOL_ALIGN16 is 0. If we are here then the user
    // probably compiled with CRYPTOPP_DISABLE_ASM. Normally we
    // would use the natural alignment of T. The problem we are
    // having is, some toolchains are changing the boundary for
    // 64-bit arrays. 64-bit elements require 8-byte alignment,
    // but the toolchain is laying the array out on a 4 byte
    // boundary. See GH #992 for mystery alignment,
    // https://github.com/weidai11/cryptopp/issues/992
    T* GetAlignedArray() {return m_array;}
    CRYPTOPP_ALIGN_DATA(8) T m_array[S];
 
#endif
 
    A m_fallbackAllocator;
    bool m_allocated;
};
 
/// \brief Static secure memory block with cleanup
/// \tparam T class or type
/// \tparam S fixed-size of the stack-based memory block, in elements
/// \details FixedSizeAllocatorWithCleanup provides a fixed-size, stack-
///  based allocation at compile time. The class can grow its memory
///  block at runtime if a suitable allocator is available. If size
///  grows beyond S and a suitable allocator is available, then the
///  statically allocated array is obsoleted.
/// \note This allocator can't be used with standard collections because
///  they require that all objects of the same allocator type are equivalent.
template <class T, size_t S, class A>
class FixedSizeAllocatorWithCleanup<T, S, A, false> : public AllocatorBase<T>
{
public:
    CRYPTOPP_INHERIT_ALLOCATOR_TYPES(T)
 
    /// \brief Constructs a FixedSizeAllocatorWithCleanup
    FixedSizeAllocatorWithCleanup() : m_allocated(false) {}
 
    /// \brief Allocates a block of memory
    /// \param size the count elements in the memory block
    /// \details FixedSizeAllocatorWithCleanup provides a fixed-size, stack-based
    ///  allocation at compile time. If size is less than or equal to
    ///  <tt>S</tt>, then a pointer to the static array is returned.
    /// \details The class can grow its memory block at runtime if a suitable
    ///  allocator is available. If size grows beyond S and a suitable
    ///  allocator is available, then the statically allocated array is
    ///  obsoleted. If a suitable allocator is not available, as with a
    ///  NullAllocator, then the function returns NULL and a runtime error
    ///  eventually occurs.
    /// \sa reallocate(), SecBlockWithHint
    pointer allocate(size_type size)
    {
        CRYPTOPP_ASSERT(IsAlignedOn(m_array, 8));
 
        if (size <= S && !m_allocated)
        {
            m_allocated = true;
            return GetAlignedArray();
        }
        else
            return m_fallbackAllocator.allocate(size);
    }
 
    /// \brief Allocates a block of memory
    /// \param size the count elements in the memory block
    /// \param hint an unused hint
    /// \details FixedSizeAllocatorWithCleanup provides a fixed-size, stack-
    ///  based allocation at compile time. If size is less than or equal to
    ///  S, then a pointer to the static array is returned.
    /// \details The class can grow its memory block at runtime if a suitable
    ///  allocator is available. If size grows beyond S and a suitable
    ///  allocator is available, then the statically allocated array is
    ///  obsoleted. If a suitable allocator is not available, as with a
    ///  NullAllocator, then the function returns NULL and a runtime error
    ///  eventually occurs.
    /// \sa reallocate(), SecBlockWithHint
    pointer allocate(size_type size, const void *hint)
    {
        if (size <= S && !m_allocated)
        {
            m_allocated = true;
            return GetAlignedArray();
        }
        else
            return m_fallbackAllocator.allocate(size, hint);
    }
 
    /// \brief Deallocates a block of memory
    /// \param ptr a pointer to the memory block to deallocate
    /// \param size the count elements in the memory block
    /// \details The memory block is wiped or zeroized before deallocation.
    ///  If the statically allocated memory block is active, then no
    ///  additional actions are taken after the wipe.
    /// \details If a dynamic memory block is active, then the pointer and
    ///   size are passed to the allocator for deallocation.
    void deallocate(void *ptr, size_type size)
    {
        // Avoid assert on pointer in deallocate. SecBlock regularly uses NULL
        // pointers rather returning non-NULL 0-sized pointers.
        if (ptr == GetAlignedArray())
        {
            // If the m_allocated assert fires then
            // something overwrote the flag.
            CRYPTOPP_ASSERT(size <= S);
            CRYPTOPP_ASSERT(m_allocated);
            m_allocated = false;
            SecureWipeArray((pointer)ptr, size);
        }
        else
        {
            if (ptr)
                m_fallbackAllocator.deallocate(ptr, size);
            m_allocated = false;
        }
    }
 
    /// \brief Reallocates a block of memory
    /// \param oldPtr the previous allocation
    /// \param oldSize the size of the previous allocation
    /// \param newSize the new, requested size
    /// \param preserve flag that indicates if the old allocation should
    ///  be preserved
    /// \return pointer to the new memory block
    /// \details FixedSizeAllocatorWithCleanup provides a fixed-size, stack-
    ///  based allocation at compile time. If size is less than or equal to
    ///  S, then a pointer to the static array is returned.
    /// \details The class can grow its memory block at runtime if a suitable
    ///  allocator is available. If size grows beyond S and a suitable
    ///  allocator is available, then the statically allocated array is
    ///  obsoleted. If a suitable allocator is not available, as with a
    ///  NullAllocator, then the function returns NULL and a runtime error
    ///  eventually occurs.
    /// \note size is the count of elements, and not the number of bytes.
    /// \sa reallocate(), SecBlockWithHint
    pointer reallocate(pointer oldPtr, size_type oldSize, size_type newSize, bool preserve)
    {
        if (oldPtr == GetAlignedArray() && newSize <= S)
        {
            CRYPTOPP_ASSERT(oldSize <= S);
            if (oldSize > newSize)
                SecureWipeArray(oldPtr+newSize, oldSize-newSize);
            return oldPtr;
        }
 
        pointer newPtr = allocate(newSize, NULLPTR);
        if (preserve && newSize)
        {
            const size_type copySize = STDMIN(oldSize, newSize);
            if (newPtr && oldPtr)  // GCC analyzer warning
                memcpy_s(newPtr, sizeof(T)*newSize, oldPtr, sizeof(T)*copySize);
        }
        deallocate(oldPtr, oldSize);
        return newPtr;
    }
 
    CRYPTOPP_CONSTEXPR size_type max_size() const
    {
        return STDMAX(m_fallbackAllocator.max_size(), S);
    }
 
private:
 
    // T_Align16 is false. Normally we would use the natural
    // alignment of T. The problem we are having is, some toolchains
    // are changing the boundary for 64-bit arrays. 64-bit elements
    // require 8-byte alignment, but the toolchain is laying the array
    // out on a 4 byte boundary. See GH #992 for mystery alignment,
    // https://github.com/weidai11/cryptopp/issues/992
    T* GetAlignedArray() {return m_array;}
    CRYPTOPP_ALIGN_DATA(8) T m_array[S];
 
    A m_fallbackAllocator;
    bool m_allocated;
};
 
/// \brief Secure memory block with allocator and cleanup
/// \tparam T a class or type
/// \tparam A AllocatorWithCleanup derived class for allocation and cleanup
/// \sa <A HREF="https://www.cryptopp.com/wiki/SecBlock">SecBlock</A>
///  on the Crypto++ wiki.
/// \since Crypto++ 2.0
template <class T, class A = AllocatorWithCleanup<T> >
class SecBlock
{
public:
    typedef typename A::value_type value_type;
    typedef typename A::pointer iterator;
    typedef typename A::const_pointer const_iterator;
    typedef typename A::size_type size_type;
 
    /// \brief Returns the maximum number of elements the block can hold
    /// \details <tt>ELEMS_MAX</tt> is the maximum number of elements the
    ///  <tt>SecBlock</tt> can hold. The value of <tt>ELEMS_MAX</tt> is
    ///  <tt>SIZE_MAX/sizeof(T)</tt>. <tt>std::numeric_limits</tt> was avoided
    ///  due to lack of <tt>constexpr</tt>-ness in C++03 and below.
    /// \note In C++03 and below <tt>ELEMS_MAX</tt> is a static data member of type
    ///  <tt>size_type</tt>. In C++11 and above <tt>ELEMS_MAX</tt> is an <tt>enum</tt>
    ///  inheriting from <tt>size_type</tt>. In both cases <tt>ELEMS_MAX</tt> can be
    ///  used before objects are fully constructed, and it does not suffer the
    ///  limitations of class methods like <tt>max_size</tt>.
    /// \sa <A HREF="http://github.com/weidai11/cryptopp/issues/346">Issue 346/CVE-2016-9939</A>
    /// \since Crypto++ 6.0
#if defined(CRYPTOPP_DOXYGEN_PROCESSING)
    static const size_type ELEMS_MAX = ...;
#elif defined(_MSC_VER) && (_MSC_VER <= 1400)
    static const size_type ELEMS_MAX = (~(size_type)0)/sizeof(T);
#elif defined(CRYPTOPP_CXX11_STRONG_ENUM)
    enum : size_type {ELEMS_MAX = A::ELEMS_MAX};
#else
    static const size_type ELEMS_MAX = SIZE_MAX/sizeof(T);
#endif
 
    /// \brief Construct a SecBlock with space for size elements.
    /// \param size the size of the allocation, in elements
    /// \throw std::bad_alloc
    /// \details The elements are not initialized.
    /// \since Crypto++ 2.0
    /// \note size is the count of elements, and not the number of bytes
    explicit SecBlock(size_type size=0)
        : m_mark(ELEMS_MAX), m_size(size), m_ptr(m_alloc.allocate(size, NULLPTR)) { }
 
    /// \brief Copy construct a SecBlock from another SecBlock
    /// \param t the other SecBlock
    /// \throw std::bad_alloc
    /// \since Crypto++ 2.0
    SecBlock(const SecBlock<T, A> &t)
        : m_mark(t.m_mark), m_size(t.m_size), m_ptr(m_alloc.allocate(t.m_size, NULLPTR)) {
            CRYPTOPP_ASSERT((!t.m_ptr && !m_size) || (t.m_ptr && m_size));
            if (m_ptr && t.m_ptr)
                memcpy_s(m_ptr, m_size*sizeof(T), t.m_ptr, t.m_size*sizeof(T));
        }
 
    /// \brief Construct a SecBlock from an array of elements.
    /// \param ptr a pointer to an array of T
    /// \param len the number of elements in the memory block
    /// \throw std::bad_alloc
    /// \details If <tt>ptr!=NULL</tt> and <tt>len!=0</tt>, then the block is initialized from the pointer
    ///  <tt>ptr</tt>. If <tt>ptr==NULL</tt> and <tt>len!=0</tt>, then the block is initialized to 0.
    ///  Otherwise, the block is empty and not initialized.
    /// \since Crypto++ 2.0
    /// \note size is the count of elements, and not the number of bytes
    SecBlock(const T *ptr, size_type len)
        : m_mark(ELEMS_MAX), m_size(len), m_ptr(m_alloc.allocate(len, NULLPTR)) {
            CRYPTOPP_ASSERT((!m_ptr && !m_size) || (m_ptr && m_size));
            if (m_ptr && ptr)
                memcpy_s(m_ptr, m_size*sizeof(T), ptr, len*sizeof(T));
            else if (m_ptr && m_size)
                memset(m_ptr, 0, m_size*sizeof(T));
        }
 
    ~SecBlock()
        {m_alloc.deallocate(m_ptr, STDMIN(m_size, m_mark));}
 
#ifdef __BORLANDC__
    /// \brief Cast operator
    /// \return block pointer cast to non-const <tt>T *</tt>
    /// \since Crypto++ 2.0
    operator T *() const
        {return (T*)m_ptr;}
#else
    /// \brief Cast operator
    /// \return block pointer cast to <tt>const void *</tt>
    /// \since Crypto++ 2.0
    operator const void *() const
        {return m_ptr;}
 
    /// \brief Cast operator
    /// \return block pointer cast to non-const <tt>void *</tt>
    /// \since Crypto++ 2.0
    operator void *()
        {return m_ptr;}
 
    /// \brief Cast operator
    /// \return block pointer cast to <tt>const T *</tt>
    /// \since Crypto++ 2.0
    operator const T *() const
        {return m_ptr;}
 
    /// \brief Cast operator
    /// \return block pointer cast to non-const <tt>T *</tt>
    /// \since Crypto++ 2.0
    operator T *()
        {return m_ptr;}
#endif
 
    /// \brief Provides an iterator pointing to the first element in the memory block
    /// \return iterator pointing to the first element in the memory block
    /// \since Crypto++ 2.0
    iterator begin()
        {return m_ptr;}
    /// \brief Provides a constant iterator pointing to the first element in the memory block
    /// \return constant iterator pointing to the first element in the memory block
    /// \since Crypto++ 2.0
    const_iterator begin() const
        {return m_ptr;}
    /// \brief Provides an iterator pointing beyond the last element in the memory block
    /// \return iterator pointing beyond the last element in the memory block
    /// \since Crypto++ 2.0
    iterator end()
        {return m_ptr+m_size;}
    /// \brief Provides a constant iterator pointing beyond the last element in the memory block
    /// \return constant iterator pointing beyond the last element in the memory block
    /// \since Crypto++ 2.0
    const_iterator end() const
        {return m_ptr+m_size;}
 
    /// \brief Provides a pointer to the first element in the memory block
    /// \return pointer to the first element in the memory block
    /// \since Crypto++ 2.0
    typename A::pointer data() {return m_ptr;}
    /// \brief Provides a pointer to the first element in the memory block
    /// \return constant pointer to the first element in the memory block
    /// \since Crypto++ 2.0
    typename A::const_pointer data() const {return m_ptr;}
 
    /// \brief Provides the count of elements in the SecBlock
    /// \return number of elements in the memory block
    /// \note the return value is the count of elements, and not the number of bytes
    /// \since Crypto++ 2.0
    size_type size() const {return m_size;}
    /// \brief Determines if the SecBlock is empty
    /// \return true if number of elements in the memory block is 0, false otherwise
    /// \since Crypto++ 2.0
    bool empty() const {return m_size == 0;}
 
    /// \brief Provides a byte pointer to the first element in the memory block
    /// \return byte pointer to the first element in the memory block
    /// \since Crypto++ 2.0
    byte * BytePtr() {return (byte *)m_ptr;}
    /// \brief Return a byte pointer to the first element in the memory block
    /// \return constant byte pointer to the first element in the memory block
    /// \since Crypto++ 2.0
    const byte * BytePtr() const {return (const byte *)m_ptr;}
    /// \brief Provides the number of bytes in the SecBlock
    /// \return the number of bytes in the memory block
    /// \note the return value is the number of bytes, and not count of elements.
    /// \since Crypto++ 2.0
    size_type SizeInBytes() const {return m_size*sizeof(T);}
 
    /// \brief Set contents and size from an array
    /// \param ptr a pointer to an array of T
    /// \param len the number of elements in the memory block
    /// \details The array pointed to by <tt>ptr</tt> must be distinct
    ///  from this SecBlock because Assign() calls New() and then memcpy().
    ///  The call to New() will invalidate all pointers and iterators, like
    ///  the pointer returned from data().
    /// \details If the memory block is reduced in size, then the reclaimed
    ///  memory is set to 0. If an assignment occurs, then Assign() resets
    ///  the element count after the previous block is zeroized.
    /// \since Crypto++ 2.0
    void Assign(const T *ptr, size_type len)
    {
        New(len);
        if (m_ptr && ptr)  // GCC analyzer warning
            memcpy_s(m_ptr, m_size*sizeof(T), ptr, len*sizeof(T));
        m_mark = ELEMS_MAX;
    }
 
    /// \brief Set contents from a value
    /// \param count the number of values to copy
    /// \param value the value, repeated count times
    /// \details If the memory block is reduced in size, then the reclaimed
    ///  memory is set to 0. If an assignment occurs, then Assign() resets
    ///  the element count after the previous block is zeroized.
    /// \since Crypto++ 6.0
    void Assign(size_type count, T value)
    {
        New(count);
        for (size_t i=0; i<count; ++i)
            m_ptr[i] = value;
        m_mark = ELEMS_MAX;
    }
 
    /// \brief Copy contents from another SecBlock
    /// \param t the other SecBlock
    /// \details Assign checks for self assignment.
    /// \details If the memory block is reduced in size, then the reclaimed
    ///  memory is set to 0. If an assignment occurs, then Assign() resets
    ///  the element count after the previous block is zeroized.
    /// \since Crypto++ 2.0
    void Assign(const SecBlock<T, A> &t)
    {
        if (this != &t)
        {
            New(t.m_size);
            if (m_ptr && t.m_ptr)  // GCC analyzer warning
                memcpy_s(m_ptr, m_size*sizeof(T), t, t.m_size*sizeof(T));
        }
        m_mark = ELEMS_MAX;
    }
 
    /// \brief Append contents from an array
    /// \param ptr a pointer to an array of T
    /// \param len the number of elements in the memory block
    /// \throw InvalidArgument if resulting size would overflow
    /// \details The array pointed to by <tt>ptr</tt> must be distinct
    ///  from this SecBlock because Append() calls Grow() and then memcpy().
    ///  The call to Grow() will invalidate all pointers and iterators, like
    ///  the pointer returned from data().
    /// \details Append() may be less efficient than a ByteQueue because
    ///  Append() must Grow() the internal array and then copy elements.
    ///  The ByteQueue can copy elements without growing.
    /// \sa ByteQueue
    /// \since Crypto++ 8.6
    void Append(const T *ptr, size_type len)
    {
        if (ELEMS_MAX - m_size < len)
            throw InvalidArgument("SecBlock: buffer overflow");
 
        const size_type oldSize = m_size;
        Grow(m_size+len);
        if (m_ptr && ptr)  // GCC analyzer warning
            memcpy_s(m_ptr+oldSize, (m_size-oldSize)*sizeof(T), ptr, len*sizeof(T));
        m_mark = ELEMS_MAX;
    }
 
    /// \brief Append contents from another SecBlock
    /// \param t the other SecBlock
    /// \throw InvalidArgument if resulting size would overflow
    /// \details Internally, this SecBlock calls Grow() and then appends t.
    /// \details Append() may be less efficient than a ByteQueue because
    ///  Append() must Grow() the internal array and then copy elements.
    ///  The ByteQueue can copy elements without growing.
    /// \sa ByteQueue
    /// \since Crypto++ 8.6
    void Append(const SecBlock<T, A> &t)
    {
        if (ELEMS_MAX - m_size < t.m_size)
            throw InvalidArgument("SecBlock: buffer overflow");
 
        const size_type oldSize = m_size;
        if (this != &t)  // s += t
        {
            Grow(m_size+t.m_size);
            if (m_ptr && t.m_ptr)  // GCC analyzer warning
                memcpy_s(m_ptr+oldSize, (m_size-oldSize)*sizeof(T), t.m_ptr, t.m_size*sizeof(T));
        }
        else            // t += t
        {
            Grow(m_size*2);
            if (m_ptr)  // GCC analyzer warning
                memmove_s(m_ptr+oldSize, (m_size-oldSize)*sizeof(T), m_ptr, oldSize*sizeof(T));
        }
        m_mark = ELEMS_MAX;
    }
 
    /// \brief Append contents from a value
    /// \param count the number of values to copy
    /// \param value the value, repeated count times
    /// \throw InvalidArgument if resulting size would overflow
    /// \details Internally, this SecBlock calls Grow() and then appends value.
    /// \details Append() may be less efficient than a ByteQueue because
    ///  Append() must Grow() the internal array and then copy elements.
    ///  The ByteQueue can copy elements without growing.
    /// \sa ByteQueue
    /// \since Crypto++ 8.6
    void Append(size_type count, T value)
    {
        if (ELEMS_MAX - m_size < count)
            throw InvalidArgument("SecBlock: buffer overflow");
 
        const size_type oldSize = m_size;
        Grow(m_size+count);
        for (size_t i=oldSize; i<oldSize+count; ++i)
            m_ptr[i] = value;
        m_mark = ELEMS_MAX;
    }
 
    /// \brief Sets the number of elements to zeroize
    /// \param count the number of elements
    /// \details SetMark is a remediation for Issue 346/CVE-2016-9939 while
    ///  preserving the streaming interface. The <tt>count</tt> controls the number of
    ///  elements zeroized, which can be less than <tt>size</tt> or 0.
    /// \details An internal variable, <tt>m_mark</tt>, is initialized to the maximum number
    ///  of elements. The maximum number of elements is <tt>ELEMS_MAX</tt>. Deallocation
    ///  triggers a zeroization, and the number of elements zeroized is
    ///  <tt>STDMIN(m_size, m_mark)</tt>. After zeroization, the memory is returned to the
    ///  system.
    /// \details The ASN.1 decoder uses SetMark() to set the element count to 0
    ///  before throwing an exception. In this case, the attacker provides a large
    ///  BER encoded length (say 64MB) but only a small number of content octets
    ///  (say 16). If the allocator zeroized all 64MB, then a transient DoS could
    ///  occur as CPU cycles are spent zeroizing uninitialized memory.
    /// \details Generally speaking, any operation which changes the size of the SecBlock
    ///  results in the mark being reset to <tt>ELEMS_MAX</tt>. In particular, if Assign(),
    ///  New(), Grow(), CleanNew(), CleanGrow() are called, then the count is reset to
    ///  <tt>ELEMS_MAX</tt>. The list is not exhaustive.
    /// \since Crypto++ 6.0
    /// \sa <A HREF="http://github.com/weidai11/cryptopp/issues/346">Issue 346/CVE-2016-9939</A>
    void SetMark(size_t count) {m_mark = count;}
 
    /// \brief Assign contents from another SecBlock
    /// \param t the other SecBlock
    /// \return reference to this SecBlock
    /// \details Internally, operator=() calls Assign().
    /// \details If the memory block is reduced in size, then the reclaimed
    ///  memory is set to 0. If an assignment occurs, then Assign() resets
    ///  the element count after the previous block is zeroized.
    /// \since Crypto++ 2.0
    SecBlock<T, A>& operator=(const SecBlock<T, A> &t)
    {
        // Assign guards for self-assignment
        Assign(t);
        return *this;
    }
 
    /// \brief Append contents from another SecBlock
    /// \param t the other SecBlock
    /// \return reference to this SecBlock
    /// \details Internally, operator+=() calls Append().
    /// \since Crypto++ 2.0
    SecBlock<T, A>& operator+=(const SecBlock<T, A> &t)
    {
        // Append guards for overflow
        Append(t);
        return *this;
    }
 
    /// \brief Construct a SecBlock from this and another SecBlock
    /// \param t the other SecBlock
    /// \return a newly constructed SecBlock that is a concatenation of this
    ///  and t.
    /// \details Internally, a new SecBlock is created from this and a
    ///  concatenation of t.
    /// \since Crypto++ 2.0
    SecBlock<T, A> operator+(const SecBlock<T, A> &t)
    {
        CRYPTOPP_ASSERT((!m_ptr && !m_size) || (m_ptr && m_size));
        CRYPTOPP_ASSERT((!t.m_ptr && !t.m_size) || (t.m_ptr && t.m_size));
        if(!t.m_size) return SecBlock(*this);
 
        SecBlock<T, A> result(m_size+t.m_size);
        if (m_size)
            memcpy_s(result.m_ptr, result.m_size*sizeof(T), m_ptr, m_size*sizeof(T));
        if (result.m_ptr && t.m_ptr)  // GCC analyzer warning
            memcpy_s(result.m_ptr+m_size, (result.m_size-m_size)*sizeof(T), t.m_ptr, t.m_size*sizeof(T));
        return result;
    }
 
    /// \brief Bitwise compare two SecBlocks
    /// \param t the other SecBlock
    /// \return true if the size and bits are equal, false otherwise
    /// \details Uses a constant time compare if the arrays are equal size.
    ///  The constant time compare is VerifyBufsEqual() found in
    ///  <tt>misc.h</tt>.
    /// \sa operator!=()
    /// \since Crypto++ 2.0
    bool operator==(const SecBlock<T, A> &t) const
    {
        return m_size == t.m_size && VerifyBufsEqual(
            reinterpret_cast<const byte*>(m_ptr),
            reinterpret_cast<const byte*>(t.m_ptr), m_size*sizeof(T));
    }
 
    /// \brief Bitwise compare two SecBlocks
    /// \param t the other SecBlock
    /// \return true if the size and bits are equal, false otherwise
    /// \details Uses a constant time compare if the arrays are equal size.
    ///  The constant time compare is VerifyBufsEqual() found in
    ///  <tt>misc.h</tt>.
    /// \details Internally, operator!=() returns the inverse of operator==().
    /// \sa operator==()
    /// \since Crypto++ 2.0
    bool operator!=(const SecBlock<T, A> &t) const
    {
        return !operator==(t);
    }
 
    /// \brief Change size without preserving contents
    /// \param newSize the new size of the memory block
    /// \details Old content is not preserved. If the memory block is
    ///  reduced in size, then the reclaimed content is set to 0. If the
    ///  memory block grows in size, then the new memory is initialized
    ///  to 0. New() resets the element count after the previous block
    ///  is zeroized.
    /// \details Internally, this SecBlock calls reallocate().
    /// \sa New(), CleanNew(), Grow(), CleanGrow(), resize()
    /// \since Crypto++ 2.0
    void New(size_type newSize)
    {
        m_ptr = m_alloc.reallocate(m_ptr, m_size, newSize, false);
        m_size = newSize;
        m_mark = ELEMS_MAX;
    }
 
    /// \brief Change size without preserving contents
    /// \param newSize the new size of the memory block
    /// \details Old content is not preserved. If the memory block is
    ///  reduced in size, then the reclaimed content is set to 0. If the
    ///  memory block grows in size, then the new memory is initialized
    ///  to 0. CleanNew() resets the element count after the previous
    ///  block is zeroized.
    /// \details Internally, this SecBlock calls New().
    /// \sa New(), CleanNew(), Grow(), CleanGrow(), resize()
    /// \since Crypto++ 2.0
    void CleanNew(size_type newSize)
    {
        New(newSize);
        if (m_ptr) {memset_z(m_ptr, 0, m_size*sizeof(T));}
        m_mark = ELEMS_MAX;
    }
 
    /// \brief Change size and preserve contents
    /// \param newSize the new size of the memory block
    /// \details Old content is preserved. New content is not initialized.
    /// \details Internally, this SecBlock calls reallocate() when size must
    ///  increase. If the size does not increase, then CleanGrow() does not
    ///  take action. If the size must change, then use resize(). CleanGrow()
    ///  resets the element count after the previous block is zeroized.
    /// \sa New(), CleanNew(), Grow(), CleanGrow(), resize()
    /// \sa New(), CleanNew(), Grow(), CleanGrow(), resize()
    /// \since Crypto++ 2.0
    void Grow(size_type newSize)
    {
        if (newSize > m_size)
        {
            m_ptr = m_alloc.reallocate(m_ptr, m_size, newSize, true);
            m_size = newSize;
        }
        m_mark = ELEMS_MAX;
    }
 
    /// \brief Change size and preserve contents
    /// \param newSize the new size of the memory block
    /// \details Old content is preserved. New content is initialized to 0.
    /// \details Internally, this SecBlock calls reallocate() when size must
    ///  increase. If the size does not increase, then CleanGrow() does not
    ///  take action. If the size must change, then use resize(). CleanGrow()
    ///  resets the element count after the previous block is zeroized.
    /// \sa New(), CleanNew(), Grow(), CleanGrow(), resize()
    /// \since Crypto++ 2.0
    void CleanGrow(size_type newSize)
    {
        if (newSize > m_size)
        {
            m_ptr = m_alloc.reallocate(m_ptr, m_size, newSize, true);
            memset_z(m_ptr+m_size, 0, (newSize-m_size)*sizeof(T));
            m_size = newSize;
        }
        m_mark = ELEMS_MAX;
    }
 
    /// \brief Change size and preserve contents
    /// \param newSize the new size of the memory block
    /// \details Old content is preserved. If the memory block grows in size, then
    ///  new memory is not initialized. resize() resets the element count after
    ///  the previous block is zeroized.
    /// \details Internally, this SecBlock calls reallocate().
    /// \sa New(), CleanNew(), Grow(), CleanGrow(), resize()
    /// \since Crypto++ 2.0
    void resize(size_type newSize)
    {
        m_ptr = m_alloc.reallocate(m_ptr, m_size, newSize, true);
        m_size = newSize;
        m_mark = ELEMS_MAX;
    }
 
    /// \brief Swap contents with another SecBlock
    /// \param b the other SecBlock
    /// \details Internally, std::swap() is called on m_alloc, m_size and m_ptr.
    /// \since Crypto++ 2.0
    void swap(SecBlock<T, A> &b)
    {
        // Swap must occur on the allocator in case its FixedSize that spilled into the heap.
        std::swap(m_alloc, b.m_alloc);
        std::swap(m_mark, b.m_mark);
        std::swap(m_size, b.m_size);
        std::swap(m_ptr, b.m_ptr);
    }
 
protected:
    A m_alloc;
    size_type m_mark, m_size;
    T *m_ptr;
};
 
#ifdef CRYPTOPP_DOXYGEN_PROCESSING
/// \brief \ref SecBlock "SecBlock<byte>" typedef.
class SecByteBlock : public SecBlock<byte> {};
/// \brief \ref SecBlock "SecBlock<word>" typedef.
class SecWordBlock : public SecBlock<word> {};
/// \brief SecBlock using \ref AllocatorWithCleanup "AllocatorWithCleanup<byte, true>" typedef
class AlignedSecByteBlock : public SecBlock<byte, AllocatorWithCleanup<byte, true> > {};
#else
typedef SecBlock<byte> SecByteBlock;
typedef SecBlock<word> SecWordBlock;
typedef SecBlock<byte, AllocatorWithCleanup<byte, true> > AlignedSecByteBlock;
#endif
 
// No need for move semantics on derived class *if* the class does not add any
// data members; see http://stackoverflow.com/q/31755703, and Rule of {0|3|5}.
 
/// \brief Fixed size stack-based SecBlock
/// \tparam T class or type
/// \tparam S fixed-size of the stack-based memory block, in elements
/// \tparam A AllocatorBase derived class for allocation and cleanup
template <class T, unsigned int S, class A = FixedSizeAllocatorWithCleanup<T, S> >
class FixedSizeSecBlock : public SecBlock<T, A>
{
public:
    /// \brief Construct a FixedSizeSecBlock
    explicit FixedSizeSecBlock() : SecBlock<T, A>(S) {}
};
 
/// \brief Fixed size stack-based SecBlock with 16-byte alignment
/// \tparam T class or type
/// \tparam S fixed-size of the stack-based memory block, in elements
/// \tparam T_Align16 boolean that determines whether allocations should be
///  aligned on a 16-byte boundary
template <class T, unsigned int S, bool T_Align16 = true>
class FixedSizeAlignedSecBlock : public FixedSizeSecBlock<T, S, FixedSizeAllocatorWithCleanup<T, S, NullAllocator<T>, T_Align16> >
{
};
 
/// \brief Stack-based SecBlock that grows into the heap
/// \tparam T class or type
/// \tparam S fixed-size of the stack-based memory block, in elements
/// \tparam A AllocatorBase derived class for allocation and cleanup
template <class T, unsigned int S, class A = FixedSizeAllocatorWithCleanup<T, S, AllocatorWithCleanup<T> > >
class SecBlockWithHint : public SecBlock<T, A>
{
public:
    /// construct a SecBlockWithHint with a count of elements
    explicit SecBlockWithHint(size_t size) : SecBlock<T, A>(size) {}
};
 
template<class T, bool A, class V, bool B>
inline bool operator==(const CryptoPP::AllocatorWithCleanup<T, A>&, const CryptoPP::AllocatorWithCleanup<V, B>&) {return (true);}
template<class T, bool A, class V, bool B>
inline bool operator!=(const CryptoPP::AllocatorWithCleanup<T, A>&, const CryptoPP::AllocatorWithCleanup<V, B>&) {return (false);}
 
NAMESPACE_END
 
NAMESPACE_BEGIN(std)
 
/// \brief Swap two SecBlocks
/// \tparam T class or type
/// \tparam A AllocatorBase derived class for allocation and cleanup
/// \param a the first SecBlock
/// \param b the second SecBlock
template <class T, class A>
inline void swap(CryptoPP::SecBlock<T, A> &a, CryptoPP::SecBlock<T, A> &b)
{
    a.swap(b);
}
 
#if defined(_STLP_DONT_SUPPORT_REBIND_MEMBER_TEMPLATE) || (defined(_STLPORT_VERSION) && !defined(_STLP_MEMBER_TEMPLATE_CLASSES))
// working for STLport 5.1.3 and MSVC 6 SP5
template <class _Tp1, class _Tp2>
inline CryptoPP::AllocatorWithCleanup<_Tp2>&
__stl_alloc_rebind(CryptoPP::AllocatorWithCleanup<_Tp1>& __a, const _Tp2*)
{
    return (CryptoPP::AllocatorWithCleanup<_Tp2>&)(__a);
}
#endif
 
NAMESPACE_END
 
#if CRYPTOPP_MSC_VERSION
# pragma warning(pop)
#endif
 
#endif