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/*
* Modular Exponentiator
* (C) 1999-2007 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#ifndef BOTAN_POWER_MOD_H__
#define BOTAN_POWER_MOD_H__
#include <botan/bigint.h>
namespace Botan {
/**
* Modular Exponentiator Interface
*/
class BOTAN_DLL Modular_Exponentiator
{
public:
virtual void set_base(const BigInt&) = 0;
virtual void set_exponent(const BigInt&) = 0;
virtual BigInt execute() const = 0;
virtual Modular_Exponentiator* copy() const = 0;
Modular_Exponentiator() = default;
Modular_Exponentiator(const Modular_Exponentiator&) = default;
Modular_Exponentiator & operator=(const Modular_Exponentiator&) = default;
virtual ~Modular_Exponentiator() = default;
};
/**
* Modular Exponentiator Proxy
*/
class BOTAN_DLL Power_Mod
{
public:
enum Usage_Hints {
NO_HINTS = 0x0000,
BASE_IS_FIXED = 0x0001,
BASE_IS_SMALL = 0x0002,
BASE_IS_LARGE = 0x0004,
BASE_IS_2 = 0x0008,
EXP_IS_FIXED = 0x0100,
EXP_IS_SMALL = 0x0200,
EXP_IS_LARGE = 0x0400
};
/*
* Try to choose a good window size
*/
static size_t window_bits(size_t exp_bits, size_t base_bits,
Power_Mod::Usage_Hints hints);
/**
* @param modulus the modulus
* @param hints Passed to set_modulus if modulus > 0
* @param disable_montgomery_arith Disables use of Montgomery
* representation. Likely only useful for testing.
*/
void set_modulus(const BigInt& modulus,
Usage_Hints = NO_HINTS,
bool disable_montgomery_arith = false) const;
/**
* Set the base
*/
void set_base(const BigInt& base) const;
/**
* Set the exponent
*/
void set_exponent(const BigInt& exponent) const;
/**
* All three of the above functions must have already been called.
* @return result of g^x%p
*/
BigInt execute() const;
Power_Mod& operator=(const Power_Mod&);
/**
* @param modulus Optionally call set_modulus
* @param hints Passed to set_modulus if modulus > 0
* @param disable_montgomery_arith Disables use of Montgomery
* representation. Likely only useful for testing.
*/
Power_Mod(const BigInt& modulus = 0,
Usage_Hints hints = NO_HINTS,
bool disable_montgomery_arith = false);
Power_Mod(const Power_Mod&);
virtual ~Power_Mod();
private:
mutable Modular_Exponentiator* m_core;
};
/**
* Fixed Exponent Modular Exponentiator Proxy
*/
class BOTAN_DLL Fixed_Exponent_Power_Mod : public Power_Mod
{
public:
BigInt operator()(const BigInt& b) const
{ set_base(b); return execute(); }
Fixed_Exponent_Power_Mod() = default;
Fixed_Exponent_Power_Mod(const BigInt& exponent,
const BigInt& modulus,
Usage_Hints hints = NO_HINTS);
};
/**
* Fixed Base Modular Exponentiator Proxy
*/
class BOTAN_DLL Fixed_Base_Power_Mod : public Power_Mod
{
public:
BigInt operator()(const BigInt& e) const
{ set_exponent(e); return execute(); }
Fixed_Base_Power_Mod() = default;
Fixed_Base_Power_Mod(const BigInt& base,
const BigInt& modulus,
Usage_Hints hints = NO_HINTS);
};
}
#endif
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