strciphr.h

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// strciphr.h - originally written and placed in the public domain by Wei Dai

/// \file strciphr.h
/// \brief Classes for implementing stream ciphers
/// \details This file contains helper classes for implementing stream ciphers.
///   All this infrastructure may look very complex compared to what's in Crypto++ 4.x,
///   but stream ciphers implementations now support a lot of new functionality,
///   including better performance (minimizing copying), resetting of keys and IVs, and
///   methods to query which features are supported by a cipher.
/// \details Here's an explanation of these classes. The word "policy" is used here to
///   mean a class with a set of methods that must be implemented by individual stream
///   cipher implementations. This is usually much simpler than the full stream cipher
///   API, which is implemented by either AdditiveCipherTemplate or CFB_CipherTemplate
///   using the policy. So for example, an implementation of SEAL only needs to implement
///   the AdditiveCipherAbstractPolicy interface (since it's an additive cipher, i.e., it
///   xors a keystream into the plaintext). See this line in seal.h:
/// <pre>
///     typedef SymmetricCipherFinal<ConcretePolicyHolder<SEAL_Policy<B>, AdditiveCipherTemplate<> > > Encryption;
/// </pre>
/// \details AdditiveCipherTemplate and CFB_CipherTemplate are designed so that they don't
///   need to take a policy class as a template parameter (although this is allowed), so
///   that their code is not duplicated for each new cipher. Instead they each get a
///   reference to an abstract policy interface by calling AccessPolicy() on itself, so
///   AccessPolicy() must be overridden to return the actual policy reference. This is done
///   by the ConceretePolicyHolder class. Finally, SymmetricCipherFinal implements the
///   constructors and other functions that must be implemented by the most derived class.

#ifndef CRYPTOPP_STRCIPHR_H
#define CRYPTOPP_STRCIPHR_H

#include "config.h"

#if CRYPTOPP_MSC_VERSION
# pragma warning(push)
# pragma warning(disable: 4127 4189 4231 4275)
#endif

#include "cryptlib.h"
#include "seckey.h"
#include "secblock.h"
#include "argnames.h"

NAMESPACE_BEGIN(CryptoPP)

/// \brief Access a stream cipher policy object
/// \tparam POLICY_INTERFACE class implementing AbstractPolicyHolder
/// \tparam BASE class or type to use as a base class
template <class POLICY_INTERFACE, class BASE = Empty>
class CRYPTOPP_NO_VTABLE AbstractPolicyHolder : public BASE
{
public:
    typedef POLICY_INTERFACE PolicyInterface;
    virtual ~AbstractPolicyHolder() {}

protected:
    virtual const POLICY_INTERFACE & GetPolicy() const =0;
    virtual POLICY_INTERFACE & AccessPolicy() =0;
};

/// \brief Stream cipher policy object
/// \tparam POLICY class implementing AbstractPolicyHolder
/// \tparam BASE class or type to use as a base class
template <class POLICY, class BASE, class POLICY_INTERFACE = typename BASE::PolicyInterface>
class ConcretePolicyHolder : public BASE, protected POLICY
{
public:
    virtual ~ConcretePolicyHolder() {}
protected:
    const POLICY_INTERFACE & GetPolicy() const {return *this;}
    POLICY_INTERFACE & AccessPolicy() {return *this;}
};

/// \brief Keystream operation flags
/// \sa AdditiveCipherAbstractPolicy::GetBytesPerIteration(), AdditiveCipherAbstractPolicy::GetOptimalBlockSize()
///   and AdditiveCipherAbstractPolicy::GetAlignment()
enum KeystreamOperationFlags {
    /// \brief Output buffer is aligned
    OUTPUT_ALIGNED=1,
    /// \brief Input buffer is aligned
    INPUT_ALIGNED=2,
    /// \brief Input buffer is NULL
    INPUT_NULL = 4
};

/// \brief Keystream operation flags
/// \sa AdditiveCipherAbstractPolicy::GetBytesPerIteration(), AdditiveCipherAbstractPolicy::GetOptimalBlockSize()
///   and AdditiveCipherAbstractPolicy::GetAlignment()
enum KeystreamOperation {
    /// \brief Wirte the keystream to the output buffer, input is NULL
    WRITE_KEYSTREAM             = INPUT_NULL,
    /// \brief Wirte the keystream to the aligned output buffer, input is NULL
    WRITE_KEYSTREAM_ALIGNED     = INPUT_NULL | OUTPUT_ALIGNED,
    /// \brief XOR the input buffer and keystream, write to the output buffer
    XOR_KEYSTREAM               = 0,
    /// \brief XOR the aligned input buffer and keystream, write to the output buffer
    XOR_KEYSTREAM_INPUT_ALIGNED = INPUT_ALIGNED,
    /// \brief XOR the input buffer and keystream, write to the aligned output buffer
    XOR_KEYSTREAM_OUTPUT_ALIGNED= OUTPUT_ALIGNED,
    /// \brief XOR the aligned input buffer and keystream, write to the aligned output buffer
    XOR_KEYSTREAM_BOTH_ALIGNED  = OUTPUT_ALIGNED | INPUT_ALIGNED
};

/// \brief Policy object for additive stream ciphers
struct CRYPTOPP_DLL CRYPTOPP_NO_VTABLE AdditiveCipherAbstractPolicy
{
    virtual ~AdditiveCipherAbstractPolicy() {}

    /// \brief Provides data alignment requirements
    /// \returns data alignment requirements, in bytes
    /// \details Internally, the default implementation returns 1. If the stream cipher is implemented
    ///   using an SSE2 ASM or intrinsics, then the value returned is usually 16.
    virtual unsigned int GetAlignment() const {return 1;}

    /// \brief Provides number of bytes operated upon during an iteration
    /// \returns bytes operated upon during an iteration, in bytes
    /// \sa GetOptimalBlockSize()
    virtual unsigned int GetBytesPerIteration() const =0;

    /// \brief Provides number of ideal bytes to process
    /// \returns the ideal number of bytes to process
    /// \details Internally, the default implementation returns GetBytesPerIteration()
    /// \sa GetBytesPerIteration()
    virtual unsigned int GetOptimalBlockSize() const {return GetBytesPerIteration();}

    /// \brief Provides buffer size based on iterations
    /// \returns the buffer size based on iterations, in bytes
    virtual unsigned int GetIterationsToBuffer() const =0;

    /// \brief Generate the keystream
    /// \param keystream the key stream
    /// \param iterationCount the number of iterations to generate the key stream
    /// \sa CanOperateKeystream(), OperateKeystream(), WriteKeystream()
    virtual void WriteKeystream(byte *keystream, size_t iterationCount)
        {OperateKeystream(KeystreamOperation(INPUT_NULL | static_cast<KeystreamOperationFlags>(IsAlignedOn(keystream, GetAlignment()))), keystream, NULLPTR, iterationCount);}

    /// \brief Flag indicating
    /// \returns true if the stream can be generated independent of the transformation input, false otherwise
    /// \sa CanOperateKeystream(), OperateKeystream(), WriteKeystream()
    virtual bool CanOperateKeystream() const {return false;}

    /// \brief Operates the keystream
    /// \param operation the operation with additional flags
    /// \param output the output buffer
    /// \param input the input buffer
    /// \param iterationCount the number of iterations to perform on the input
    /// \details OperateKeystream() will attempt to operate upon GetOptimalBlockSize() buffer,
    ///   which will be derived from GetBytesPerIteration().
    /// \sa CanOperateKeystream(), OperateKeystream(), WriteKeystream(), KeystreamOperation()
    virtual void OperateKeystream(KeystreamOperation operation, byte *output, const byte *input, size_t iterationCount)
        {CRYPTOPP_UNUSED(operation); CRYPTOPP_UNUSED(output); CRYPTOPP_UNUSED(input);
        CRYPTOPP_UNUSED(iterationCount); CRYPTOPP_ASSERT(false);}

    /// \brief Key the cipher
    /// \param params set of NameValuePairs use to initialize this object
    /// \param key a byte array used to key the cipher
    /// \param length the size of the key array
    virtual void CipherSetKey(const NameValuePairs &params, const byte *key, size_t length) =0;

    /// \brief Resynchronize the cipher
    /// \param keystreamBuffer the keystream buffer
    /// \param iv a byte array used to resynchronize the cipher
    /// \param length the size of the IV array
    virtual void CipherResynchronize(byte *keystreamBuffer, const byte *iv, size_t length)
        {CRYPTOPP_UNUSED(keystreamBuffer); CRYPTOPP_UNUSED(iv); CRYPTOPP_UNUSED(length);
        throw NotImplemented("SimpleKeyingInterface: this object doesn't support resynchronization");}

    /// \brief Flag indicating random access
    /// \returns true if the cipher is seekable, false otherwise
    /// \sa SeekToIteration()
    virtual bool CipherIsRandomAccess() const =0;

    /// \brief Seeks to a random position in the stream
    /// \sa CipherIsRandomAccess()
    virtual void SeekToIteration(lword iterationCount)
        {CRYPTOPP_UNUSED(iterationCount); CRYPTOPP_ASSERT(!CipherIsRandomAccess());
        throw NotImplemented("StreamTransformation: this object doesn't support random access");}

    /// \brief Retrieve the provider of this algorithm
    /// \return the algorithm provider
    /// \details The algorithm provider can be a name like "C++", "SSE", "NEON", "AESNI",
    ///    "ARMv8" and "Power8". C++ is standard C++ code. Other labels, like SSE,
    ///    usually indicate a specialized implementation using instructions from a higher
    ///    instruction set architecture (ISA). Future labels may include external hardware
    ///    like a hardware security module (HSM).
    /// \details Generally speaking Wei Dai's original IA-32 ASM code falls under "SSE2".
    ///    Labels like "SSSE3" and "SSE4.1" follow after Wei's code and use intrinsics
    ///    instead of ASM.
    /// \details Algorithms which combine different instructions or ISAs provide the
    ///    dominant one. For example on x86 <tt>AES/GCM</tt> returns "AESNI" rather than
    ///    "CLMUL" or "AES+SSE4.1" or "AES+CLMUL" or "AES+SSE4.1+CLMUL".
    /// \note Provider is not universally implemented yet.
    virtual std::string AlgorithmProvider() const { return "C++"; }
};

/// \brief Base class for additive stream ciphers
/// \tparam WT word type
/// \tparam W count of words
/// \tparam X bytes per iteration count
/// \tparam BASE AdditiveCipherAbstractPolicy derived base class
template <typename WT, unsigned int W, unsigned int X = 1, class BASE = AdditiveCipherAbstractPolicy>
struct CRYPTOPP_NO_VTABLE AdditiveCipherConcretePolicy : public BASE
{
    /// \brief Word type for the cipher
    typedef WT WordType;

    /// \brief Number of bytes for an iteration
    /// \details BYTES_PER_ITERATION is the product <tt>sizeof(WordType) * W</tt>.
    ///  For example, ChaCha uses 16 each <tt>word32</tt>, and the value of
    ///  BYTES_PER_ITERATION is 64. Each invocation of the ChaCha block function
    ///  produces 64 bytes of keystream.
    CRYPTOPP_CONSTANT(BYTES_PER_ITERATION = sizeof(WordType) * W)

    virtual ~AdditiveCipherConcretePolicy() {}

#if !(CRYPTOPP_BOOL_X86 || CRYPTOPP_BOOL_X64)
    /// \brief Provides data alignment requirements
    /// \returns data alignment requirements, in bytes
    /// \details Internally, the default implementation returns 1. If the stream
    ///  cipher is implemented using an SSE2 ASM or intrinsics, then the value
    ///  returned is usually 16.
    unsigned int GetAlignment() const {return GetAlignmentOf<WordType>();}
#endif

    /// \brief Provides number of bytes operated upon during an iteration
    /// \returns bytes operated upon during an iteration, in bytes
    /// \sa GetOptimalBlockSize()
    unsigned int GetBytesPerIteration() const {return BYTES_PER_ITERATION;}

    /// \brief Provides buffer size based on iterations
    /// \returns the buffer size based on iterations, in bytes
    unsigned int GetIterationsToBuffer() const {return X;}

    /// \brief Flag indicating
    /// \returns true if the stream can be generated independent of the
    ///  transformation input, false otherwise
    /// \sa CanOperateKeystream(), OperateKeystream(), WriteKeystream()
    bool CanOperateKeystream() const {return true;}

    /// \brief Operates the keystream
    /// \param operation the operation with additional flags
    /// \param output the output buffer
    /// \param input the input buffer
    /// \param iterationCount the number of iterations to perform on the input
    /// \details OperateKeystream() will attempt to operate upon GetOptimalBlockSize() buffer,
    ///   which will be derived from GetBytesPerIteration().
    /// \sa CanOperateKeystream(), OperateKeystream(), WriteKeystream(), KeystreamOperation()
    virtual void OperateKeystream(KeystreamOperation operation, byte *output, const byte *input, size_t iterationCount) =0;
};

/// \brief Helper macro to implement OperateKeystream
/// \param x KeystreamOperation mask
/// \param b Endian order
/// \param i index in output buffer
/// \param a value to output
#define CRYPTOPP_KEYSTREAM_OUTPUT_WORD(x, b, i, a)  \
    PutWord(bool(x & OUTPUT_ALIGNED), b, output+i*sizeof(WordType), (x & INPUT_NULL) ? (a) : (a) ^ GetWord<WordType>(bool(x & INPUT_ALIGNED), b, input+i*sizeof(WordType)));

/// \brief Helper macro to implement OperateKeystream
/// \param x KeystreamOperation mask
/// \param i index in output buffer
/// \param a value to output
#define CRYPTOPP_KEYSTREAM_OUTPUT_XMM(x, i, a)  {\
    __m128i t = (x & INPUT_NULL) ? a : _mm_xor_si128(a, (x & INPUT_ALIGNED) ? _mm_load_si128((__m128i *)input+i) : _mm_loadu_si128((__m128i *)input+i));\
    if (x & OUTPUT_ALIGNED) _mm_store_si128((__m128i *)output+i, t);\
    else _mm_storeu_si128((__m128i *)output+i, t);}

/// \brief Helper macro to implement OperateKeystream
#define CRYPTOPP_KEYSTREAM_OUTPUT_SWITCH(x, y)  \
    switch (operation)                          \
    {                                           \
        case WRITE_KEYSTREAM:                   \
            x(WRITE_KEYSTREAM)                  \
            break;                              \
        case XOR_KEYSTREAM:                     \
            x(XOR_KEYSTREAM)                    \
            input += y;                         \
            break;                              \
        case XOR_KEYSTREAM_INPUT_ALIGNED:       \
            x(XOR_KEYSTREAM_INPUT_ALIGNED)      \
            input += y;                         \
            break;                              \
        case XOR_KEYSTREAM_OUTPUT_ALIGNED:      \
            x(XOR_KEYSTREAM_OUTPUT_ALIGNED)     \
            input += y;                         \
            break;                              \
        case WRITE_KEYSTREAM_ALIGNED:           \
            x(WRITE_KEYSTREAM_ALIGNED)          \
            break;                              \
        case XOR_KEYSTREAM_BOTH_ALIGNED:        \
            x(XOR_KEYSTREAM_BOTH_ALIGNED)       \
            input += y;                         \
            break;                              \
    }                                           \
    output += y;

/// \brief Base class for additive stream ciphers with SymmetricCipher interface
/// \tparam BASE AbstractPolicyHolder base class
template <class BASE = AbstractPolicyHolder<AdditiveCipherAbstractPolicy, SymmetricCipher> >
class CRYPTOPP_NO_VTABLE AdditiveCipherTemplate : public BASE, public RandomNumberGenerator
{
public:
    virtual ~AdditiveCipherTemplate() {}
    AdditiveCipherTemplate() : m_leftOver(0) {}

    /// \brief Generate random array of bytes
    /// \param output the byte buffer
    /// \param size the length of the buffer, in bytes
    /// \details All generated values are uniformly distributed over the range specified
    ///   within the constraints of a particular generator.
    void GenerateBlock(byte *output, size_t size);

    /// \brief Apply keystream to data
    /// \param outString a buffer to write the transformed data
    /// \param inString a buffer to read the data
    /// \param length the size fo the buffers, in bytes
    /// \details This is the primary method to operate a stream cipher. For example:
    /// <pre>
    ///     size_t size = 30;
    ///     byte plain[size] = "Do or do not; there is no try";
    ///     byte cipher[size];
    ///     ...
    ///     ChaCha20 chacha(key, keySize);
    ///     chacha.ProcessData(cipher, plain, size);
    /// </pre>
    void ProcessData(byte *outString, const byte *inString, size_t length);

    /// \brief Resynchronize the cipher
    /// \param iv a byte array used to resynchronize the cipher
    /// \param length the size of the IV array
    void Resynchronize(const byte *iv, int length=-1);

    /// \brief Provides number of ideal bytes to process
    /// \returns the ideal number of bytes to process
    /// \details Internally, the default implementation returns GetBytesPerIteration()
    /// \sa GetBytesPerIteration() and GetOptimalNextBlockSize()
    unsigned int OptimalBlockSize() const {return this->GetPolicy().GetOptimalBlockSize();}

    /// \brief Provides number of ideal bytes to process
    /// \returns the ideal number of bytes to process
    /// \details Internally, the default implementation returns remaining unprocessed bytes
    /// \sa GetBytesPerIteration() and OptimalBlockSize()
    unsigned int GetOptimalNextBlockSize() const {return (unsigned int)this->m_leftOver;}

    /// \brief Provides number of ideal data alignment
    /// \returns the ideal data alignment, in bytes
    /// \sa GetAlignment() and OptimalBlockSize()
    unsigned int OptimalDataAlignment() const {return this->GetPolicy().GetAlignment();}

    /// \brief Determines if the cipher is self inverting
    /// \returns true if the stream cipher is self inverting, false otherwise
    bool IsSelfInverting() const {return true;}

    /// \brief Determines if the cipher is a forward transformation
    /// \returns true if the stream cipher is a forward transformation, false otherwise
    bool IsForwardTransformation() const {return true;}

    /// \brief Flag indicating random access
    /// \returns true if the cipher is seekable, false otherwise
    /// \sa Seek()
    bool IsRandomAccess() const {return this->GetPolicy().CipherIsRandomAccess();}

    /// \brief Seeks to a random position in the stream
    /// \param position the absolute position in the stream
    /// \sa IsRandomAccess()
    void Seek(lword position);

    /// \brief Retrieve the provider of this algorithm
    /// \return the algorithm provider
    /// \details The algorithm provider can be a name like "C++", "SSE", "NEON", "AESNI",
    ///    "ARMv8" and "Power8". C++ is standard C++ code. Other labels, like SSE,
    ///    usually indicate a specialized implementation using instructions from a higher
    ///    instruction set architecture (ISA). Future labels may include external hardware
    ///    like a hardware security module (HSM).
    /// \details Generally speaking Wei Dai's original IA-32 ASM code falls under "SSE2".
    ///    Labels like "SSSE3" and "SSE4.1" follow after Wei's code and use intrinsics
    ///    instead of ASM.
    /// \details Algorithms which combine different instructions or ISAs provide the
    ///    dominant one. For example on x86 <tt>AES/GCM</tt> returns "AESNI" rather than
    ///    "CLMUL" or "AES+SSE4.1" or "AES+CLMUL" or "AES+SSE4.1+CLMUL".
    /// \note Provider is not universally implemented yet.
    std::string AlgorithmProvider() const { return this->GetPolicy().AlgorithmProvider(); }

    typedef typename BASE::PolicyInterface PolicyInterface;

protected:
    void UncheckedSetKey(const byte *key, unsigned int length, const NameValuePairs &params);

    unsigned int GetBufferByteSize(const PolicyInterface &policy) const {return policy.GetBytesPerIteration() * policy.GetIterationsToBuffer();}

    inline byte * KeystreamBufferBegin() {return this->m_buffer.data();}
    inline byte * KeystreamBufferEnd() {return (PtrAdd(this->m_buffer.data(), this->m_buffer.size()));}

    AlignedSecByteBlock m_buffer;
    size_t m_leftOver;
};

/// \brief Policy object for feeback based stream ciphers
class CRYPTOPP_DLL CRYPTOPP_NO_VTABLE CFB_CipherAbstractPolicy
{
public:
    virtual ~CFB_CipherAbstractPolicy() {}

    /// \brief Provides data alignment requirements
    /// \returns data alignment requirements, in bytes
    /// \details Internally, the default implementation returns 1. If the stream cipher is implemented
    ///   using an SSE2 ASM or intrinsics, then the value returned is usually 16.
    virtual unsigned int GetAlignment() const =0;

    /// \brief Provides number of bytes operated upon during an iteration
    /// \returns bytes operated upon during an iteration, in bytes
    /// \sa GetOptimalBlockSize()
    virtual unsigned int GetBytesPerIteration() const =0;

    /// \brief Access the feedback register
    /// \returns pointer to the first byte of the feedback register
    virtual byte * GetRegisterBegin() =0;

    /// \brief TODO
    virtual void TransformRegister() =0;

    /// \brief Flag indicating iteration support
    /// \returns true if the cipher supports iteration, false otherwise
    virtual bool CanIterate() const {return false;}

    /// \brief Iterate the cipher
    /// \param output the output buffer
    /// \param input the input buffer
    /// \param dir the direction of the cipher
    /// \param iterationCount the number of iterations to perform on the input
    /// \sa IsSelfInverting() and IsForwardTransformation()
    virtual void Iterate(byte *output, const byte *input, CipherDir dir, size_t iterationCount)
        {CRYPTOPP_UNUSED(output); CRYPTOPP_UNUSED(input); CRYPTOPP_UNUSED(dir);
        CRYPTOPP_UNUSED(iterationCount); CRYPTOPP_ASSERT(false);
        throw Exception(Exception::OTHER_ERROR, "SimpleKeyingInterface: unexpected error");}

    /// \brief Key the cipher
    /// \param params set of NameValuePairs use to initialize this object
    /// \param key a byte array used to key the cipher
    /// \param length the size of the key array
    virtual void CipherSetKey(const NameValuePairs &params, const byte *key, size_t length) =0;

    /// \brief Resynchronize the cipher
    /// \param iv a byte array used to resynchronize the cipher
    /// \param length the size of the IV array
    virtual void CipherResynchronize(const byte *iv, size_t length)
        {CRYPTOPP_UNUSED(iv); CRYPTOPP_UNUSED(length);
        throw NotImplemented("SimpleKeyingInterface: this object doesn't support resynchronization");}

    /// \brief Retrieve the provider of this algorithm
    /// \return the algorithm provider
    /// \details The algorithm provider can be a name like "C++", "SSE", "NEON", "AESNI",
    ///    "ARMv8" and "Power8". C++ is standard C++ code. Other labels, like SSE,
    ///    usually indicate a specialized implementation using instructions from a higher
    ///    instruction set architecture (ISA). Future labels may include external hardware
    ///    like a hardware security module (HSM).
    /// \details Generally speaking Wei Dai's original IA-32 ASM code falls under "SSE2".
    ///    Labels like "SSSE3" and "SSE4.1" follow after Wei's code and use intrinsics
    ///    instead of ASM.
    /// \details Algorithms which combine different instructions or ISAs provide the
    ///    dominant one. For example on x86 <tt>AES/GCM</tt> returns "AESNI" rather than
    ///    "CLMUL" or "AES+SSE4.1" or "AES+CLMUL" or "AES+SSE4.1+CLMUL".
    /// \note Provider is not universally implemented yet.
    virtual std::string AlgorithmProvider() const { return "C++"; }
};

/// \brief Base class for feedback based stream ciphers
/// \tparam WT word type
/// \tparam W count of words
/// \tparam BASE CFB_CipherAbstractPolicy derived base class
template <typename WT, unsigned int W, class BASE = CFB_CipherAbstractPolicy>
struct CRYPTOPP_NO_VTABLE CFB_CipherConcretePolicy : public BASE
{
    typedef WT WordType;

    virtual ~CFB_CipherConcretePolicy() {}

    /// \brief Provides data alignment requirements
    /// \returns data alignment requirements, in bytes
    /// \details Internally, the default implementation returns 1. If the stream cipher is implemented
    ///   using an SSE2 ASM or intrinsics, then the value returned is usually 16.
    unsigned int GetAlignment() const {return sizeof(WordType);}

    /// \brief Provides number of bytes operated upon during an iteration
    /// \returns bytes operated upon during an iteration, in bytes
    /// \sa GetOptimalBlockSize()
    unsigned int GetBytesPerIteration() const {return sizeof(WordType) * W;}

    /// \brief Flag indicating iteration support
    /// \returns true if the cipher supports iteration, false otherwise
    bool CanIterate() const {return true;}

    /// \brief Perform one iteration in the forward direction
    void TransformRegister() {this->Iterate(NULLPTR, NULLPTR, ENCRYPTION, 1);}

    /// \brief Provides alternate access to a feedback register
    /// \tparam B enumeration indicating endianness
    /// \details RegisterOutput() provides alternate access to the feedback register. The
    ///   enumeration B is BigEndian or LittleEndian. Repeatedly applying operator()
    ///   results in advancing in the register.
    template <class B>
    struct RegisterOutput
    {
        RegisterOutput(byte *output, const byte *input, CipherDir dir)
            : m_output(output), m_input(input), m_dir(dir) {}

        /// \brief XOR feedback register with data
        /// \param registerWord data represented as a word type
        /// \returns reference to the next feedback register word
        inline RegisterOutput& operator()(WordType &registerWord)
        {
            //CRYPTOPP_ASSERT(IsAligned<WordType>(m_output));
            //CRYPTOPP_ASSERT(IsAligned<WordType>(m_input));

            if (!NativeByteOrderIs(B::ToEnum()))
                registerWord = ByteReverse(registerWord);

            if (m_dir == ENCRYPTION)
            {
                if (m_input == NULLPTR)
                {
                    CRYPTOPP_ASSERT(m_output == NULLPTR);
                }
                else
                {
                    // WordType ct = *(const WordType *)m_input ^ registerWord;
                    WordType ct = GetWord<WordType>(false, NativeByteOrder::ToEnum(), m_input) ^ registerWord;
                    registerWord = ct;

                    // *(WordType*)m_output = ct;
                    PutWord<WordType>(false, NativeByteOrder::ToEnum(), m_output, ct);

                    m_input += sizeof(WordType);
                    m_output += sizeof(WordType);
                }
            }
            else
            {
                // WordType ct = *(const WordType *)m_input;
                WordType ct = GetWord<WordType>(false, NativeByteOrder::ToEnum(), m_input);

                // *(WordType*)m_output = registerWord ^ ct;
                PutWord<WordType>(false, NativeByteOrder::ToEnum(), m_output, registerWord ^ ct);
                registerWord = ct;

                m_input += sizeof(WordType);
                m_output += sizeof(WordType);
            }

            // registerWord is left unreversed so it can be xor-ed with further input

            return *this;
        }

        byte *m_output;
        const byte *m_input;
        CipherDir m_dir;
    };
};

/// \brief Base class for feedback based stream ciphers with SymmetricCipher interface
/// \tparam BASE AbstractPolicyHolder base class
template <class BASE>
class CRYPTOPP_NO_VTABLE CFB_CipherTemplate : public BASE
{
public:
    virtual ~CFB_CipherTemplate() {}
    CFB_CipherTemplate() : m_leftOver(0) {}

    /// \brief Apply keystream to data
    /// \param outString a buffer to write the transformed data
    /// \param inString a buffer to read the data
    /// \param length the size fo the buffers, in bytes
    /// \details This is the primary method to operate a stream cipher. For example:
    /// <pre>
    ///     size_t size = 30;
    ///     byte plain[size] = "Do or do not; there is no try";
    ///     byte cipher[size];
    ///     ...
    ///     ChaCha20 chacha(key, keySize);
    ///     chacha.ProcessData(cipher, plain, size);
    /// </pre>
    void ProcessData(byte *outString, const byte *inString, size_t length);

    /// \brief Resynchronize the cipher
    /// \param iv a byte array used to resynchronize the cipher
    /// \param length the size of the IV array
    void Resynchronize(const byte *iv, int length=-1);

    /// \brief Provides number of ideal bytes to process
    /// \returns the ideal number of bytes to process
    /// \details Internally, the default implementation returns GetBytesPerIteration()
    /// \sa GetBytesPerIteration() and GetOptimalNextBlockSize()
    unsigned int OptimalBlockSize() const {return this->GetPolicy().GetBytesPerIteration();}

    /// \brief Provides number of ideal bytes to process
    /// \returns the ideal number of bytes to process
    /// \details Internally, the default implementation returns remaining unprocessed bytes
    /// \sa GetBytesPerIteration() and OptimalBlockSize()
    unsigned int GetOptimalNextBlockSize() const {return (unsigned int)m_leftOver;}

    /// \brief Provides number of ideal data alignment
    /// \returns the ideal data alignment, in bytes
    /// \sa GetAlignment() and OptimalBlockSize()
    unsigned int OptimalDataAlignment() const {return this->GetPolicy().GetAlignment();}

    /// \brief Flag indicating random access
    /// \returns true if the cipher is seekable, false otherwise
    /// \sa Seek()
    bool IsRandomAccess() const {return false;}

    /// \brief Determines if the cipher is self inverting
    /// \returns true if the stream cipher is self inverting, false otherwise
    bool IsSelfInverting() const {return false;}

    /// \brief Retrieve the provider of this algorithm
    /// \return the algorithm provider
    /// \details The algorithm provider can be a name like "C++", "SSE", "NEON", "AESNI",
    ///    "ARMv8" and "Power8". C++ is standard C++ code. Other labels, like SSE,
    ///    usually indicate a specialized implementation using instructions from a higher
    ///    instruction set architecture (ISA). Future labels may include external hardware
    ///    like a hardware security module (HSM).
    /// \details Generally speaking Wei Dai's original IA-32 ASM code falls under "SSE2".
    ///    Labels like "SSSE3" and "SSE4.1" follow after Wei's code and use intrinsics
    ///    instead of ASM.
    /// \details Algorithms which combine different instructions or ISAs provide the
    ///    dominant one. For example on x86 <tt>AES/GCM</tt> returns "AESNI" rather than
    ///    "CLMUL" or "AES+SSE4.1" or "AES+CLMUL" or "AES+SSE4.1+CLMUL".
    /// \note Provider is not universally implemented yet.
    std::string AlgorithmProvider() const { return this->GetPolicy().AlgorithmProvider(); }

    typedef typename BASE::PolicyInterface PolicyInterface;

protected:
    virtual void CombineMessageAndShiftRegister(byte *output, byte *reg, const byte *message, size_t length) =0;

    void UncheckedSetKey(const byte *key, unsigned int length, const NameValuePairs &params);

    size_t m_leftOver;
};

/// \brief Base class for feedback based stream ciphers in the forward direction with SymmetricCipher interface
/// \tparam BASE AbstractPolicyHolder base class
template <class BASE = AbstractPolicyHolder<CFB_CipherAbstractPolicy, SymmetricCipher> >
class CRYPTOPP_NO_VTABLE CFB_EncryptionTemplate : public CFB_CipherTemplate<BASE>
{
    bool IsForwardTransformation() const {return true;}
    void CombineMessageAndShiftRegister(byte *output, byte *reg, const byte *message, size_t length);
};

/// \brief Base class for feedback based stream ciphers in the reverse direction with SymmetricCipher interface
/// \tparam BASE AbstractPolicyHolder base class
template <class BASE = AbstractPolicyHolder<CFB_CipherAbstractPolicy, SymmetricCipher> >
class CRYPTOPP_NO_VTABLE CFB_DecryptionTemplate : public CFB_CipherTemplate<BASE>
{
    bool IsForwardTransformation() const {return false;}
    void CombineMessageAndShiftRegister(byte *output, byte *reg, const byte *message, size_t length);
};

/// \brief Base class for feedback based stream ciphers with a mandatory block size
/// \tparam BASE CFB_EncryptionTemplate or CFB_DecryptionTemplate base class
template <class BASE>
class CFB_RequireFullDataBlocks : public BASE
{
public:
    unsigned int MandatoryBlockSize() const {return this->OptimalBlockSize();}
};

/// \brief SymmetricCipher implementation
/// \tparam BASE AbstractPolicyHolder derived base class
/// \tparam INFO AbstractPolicyHolder derived information class
/// \sa Weak::ARC4, ChaCha8, ChaCha12, ChaCha20, Salsa20, SEAL, Sosemanuk, WAKE
template <class BASE, class INFO = BASE>
class SymmetricCipherFinal : public AlgorithmImpl<SimpleKeyingInterfaceImpl<BASE, INFO>, INFO>
{
public:
    virtual ~SymmetricCipherFinal() {}

    /// \brief Construct a stream cipher
    SymmetricCipherFinal() {}

    /// \brief Construct a stream cipher
    /// \param key a byte array used to key the cipher
    /// \details This overload uses DEFAULT_KEYLENGTH
    SymmetricCipherFinal(const byte *key)
        {this->SetKey(key, this->DEFAULT_KEYLENGTH);}

    /// \brief Construct a stream cipher
    /// \param key a byte array used to key the cipher
    /// \param length the size of the key array
    SymmetricCipherFinal(const byte *key, size_t length)
        {this->SetKey(key, length);}

    /// \brief Construct a stream cipher
    /// \param key a byte array used to key the cipher
    /// \param length the size of the key array
    /// \param iv a byte array used as an initialization vector
    SymmetricCipherFinal(const byte *key, size_t length, const byte *iv)
        {this->SetKeyWithIV(key, length, iv);}

    /// \brief Clone a SymmetricCipher
    /// \returns a new SymmetricCipher based on this object
    Clonable * Clone() const {return static_cast<SymmetricCipher *>(new SymmetricCipherFinal<BASE, INFO>(*this));}
};

NAMESPACE_END

#ifdef CRYPTOPP_MANUALLY_INSTANTIATE_TEMPLATES
#include "strciphr.cpp"
#endif

NAMESPACE_BEGIN(CryptoPP)
CRYPTOPP_DLL_TEMPLATE_CLASS AbstractPolicyHolder<AdditiveCipherAbstractPolicy, SymmetricCipher>;
CRYPTOPP_DLL_TEMPLATE_CLASS AdditiveCipherTemplate<AbstractPolicyHolder<AdditiveCipherAbstractPolicy, SymmetricCipher> >;
CRYPTOPP_DLL_TEMPLATE_CLASS CFB_CipherTemplate<AbstractPolicyHolder<CFB_CipherAbstractPolicy, SymmetricCipher> >;
CRYPTOPP_DLL_TEMPLATE_CLASS CFB_EncryptionTemplate<AbstractPolicyHolder<CFB_CipherAbstractPolicy, SymmetricCipher> >;
CRYPTOPP_DLL_TEMPLATE_CLASS CFB_DecryptionTemplate<AbstractPolicyHolder<CFB_CipherAbstractPolicy, SymmetricCipher> >;

NAMESPACE_END

#if CRYPTOPP_MSC_VERSION
# pragma warning(pop)
#endif

#endif