bigint.h

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/*
* BigInt
* (C) 1999-2008,2012 Jack Lloyd
*     2007 FlexSecure
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#ifndef BOTAN_BIGINT_H_
#define BOTAN_BIGINT_H_

#include <botan/types.h>
#include <botan/secmem.h>
#include <botan/exceptn.h>
#include <botan/loadstor.h>
#include <iosfwd>

namespace Botan {

class RandomNumberGenerator;

/**
* Arbitrary precision integer
*/
class BOTAN_PUBLIC_API(2,0) BigInt final
   {
   public:
     /**
     * Base enumerator for encoding and decoding
     */
     enum Base { Decimal = 10, Hexadecimal = 16, Binary = 256 };

     /**
     * Sign symbol definitions for positive and negative numbers
     */
     enum Sign { Negative = 0, Positive = 1 };

     /**
     * DivideByZero Exception
     */
     class BOTAN_PUBLIC_API(2,0) DivideByZero final : public Exception
        {
        public:
           DivideByZero() : Exception("BigInt divide by zero") {}
        };

     /**
     * Create empty BigInt
     */
     BigInt() = default;

     /**
     * Create BigInt from 64 bit integer
     * @param n initial value of this BigInt
     */
     BigInt(uint64_t n);

     /**
     * Copy Constructor
     * @param other the BigInt to copy
     */
     BigInt(const BigInt& other);

     /**
     * Create BigInt from a string. If the string starts with 0x the
     * rest of the string will be interpreted as hexadecimal digits.
     * Otherwise, it will be interpreted as a decimal number.
     *
     * @param str the string to parse for an integer value
     */
     explicit BigInt(const std::string& str);

     /**
     * Create a BigInt from an integer in a byte array
     * @param buf the byte array holding the value
     * @param length size of buf
     */
     BigInt(const uint8_t buf[], size_t length);

     /**
     * Create a BigInt from an integer in a byte array
     * @param buf the byte array holding the value
     * @param length size of buf
     * @param base is the number base of the integer in buf
     */
     BigInt(const uint8_t buf[], size_t length, Base base);

     /**
     * Create a BigInt from an integer in a byte array
     * @param buf the byte array holding the value
     * @param length size of buf
     * @param max_bits if the resulting integer is more than max_bits,
     *        it will be shifted so it is at most max_bits in length.
     */
     BigInt(const uint8_t buf[], size_t length, size_t max_bits);

     /**
     * Create a BigInt from an array of words
     * @param words the words
     * @param length number of words
     */
     BigInt(const word words[], size_t length);

     /**
     * \brief Create a random BigInt of the specified size
     *
     * @param rng random number generator
     * @param bits size in bits
     * @param set_high_bit if true, the highest bit is always set
     *
     * @see randomize
     */
     BigInt(RandomNumberGenerator& rng, size_t bits, bool set_high_bit = true);

     /**
     * Create BigInt of specified size, all zeros
     * @param sign the sign
     * @param n size of the internal register in words
     */
     BigInt(Sign sign, size_t n);

     /**
     * Move constructor
     */
     BigInt(BigInt&& other)
        {
        this->swap(other);
        }

     /**
     * Move assignment
     */
     BigInt& operator=(BigInt&& other)
        {
        if(this != &other)
           this->swap(other);

        return (*this);
        }

     /**
     * Copy assignment
     */
     BigInt& operator=(const BigInt&) = default;

     /**
     * Swap this value with another
     * @param other BigInt to swap values with
     */
     void swap(BigInt& other)
        {
        m_reg.swap(other.m_reg);
        std::swap(m_signedness, other.m_signedness);
        }

     void swap_reg(secure_vector<word>& reg)
        {
        m_reg.swap(reg);
        }

     /**
     * += operator
     * @param y the BigInt to add to this
     */
     BigInt& operator+=(const BigInt& y);

     /**
     * -= operator
     * @param y the BigInt to subtract from this
     */
     BigInt& operator-=(const BigInt& y);

     /**
     * *= operator
     * @param y the BigInt to multiply with this
     */
     BigInt& operator*=(const BigInt& y);

     /**
     * *= operator
     * @param y the word to multiply with this
     */
     BigInt& operator*=(word y);

     /**
     * /= operator
     * @param y the BigInt to divide this by
     */
     BigInt& operator/=(const BigInt& y);

     /**
     * Modulo operator
     * @param y the modulus to reduce this by
     */
     BigInt& operator%=(const BigInt& y);

     /**
     * Modulo operator
     * @param y the modulus (word) to reduce this by
     */
     word    operator%=(word y);

     /**
     * Left shift operator
     * @param shift the number of bits to shift this left by
     */
     BigInt& operator<<=(size_t shift);

     /**
     * Right shift operator
     * @param shift the number of bits to shift this right by
     */
     BigInt& operator>>=(size_t shift);

     /**
     * Increment operator
     */
     BigInt& operator++() { return (*this += 1); }

     /**
     * Decrement operator
     */
     BigInt& operator--() { return (*this -= 1); }

     /**
     * Postfix increment operator
     */
     BigInt  operator++(int) { BigInt x = (*this); ++(*this); return x; }

     /**
     * Postfix decrement operator
     */
     BigInt  operator--(int) { BigInt x = (*this); --(*this); return x; }

     /**
     * Unary negation operator
     * @return negative this
     */
     BigInt operator-() const;

     /**
     * ! operator
     * @return true iff this is zero, otherwise false
     */
     bool operator !() const { return (!is_nonzero()); }

     /**
     * Multiply this with y
     * @param y the BigInt to multiply with this
     * @param ws a temp workspace
     */
     BigInt& mul(const BigInt& y, secure_vector<word>& ws);

     /**
     * Square value of *this
     * @param ws a temp workspace
     */
     BigInt& square(secure_vector<word>& ws);

     /**
     * Set *this to y - *this
     * @param y the BigInt to subtract from as a sequence of words
     * @param y_size length of y in words
     * @param ws a temp workspace
     */
     BigInt& rev_sub(const word y[], size_t y_size, secure_vector<word>& ws);

     /**
     * Return *this below mod
     *
     * Assumes that *this is (if anything) only slightly larger than
     * mod and performs repeated subtractions. It should not be used if
     * *this is much larger than mod, instead of modulo operator.
     */
     void reduce_below(const BigInt& mod, secure_vector<word> &ws);

     /**
     * Zeroize the BigInt. The size of the underlying register is not
     * modified.
     */
     void clear() { zeroise(m_reg); }

     /**
     * Compare this to another BigInt
     * @param n the BigInt value to compare with
     * @param check_signs include sign in comparison?
     * @result if (this<n) return -1, if (this>n) return 1, if both
     * values are identical return 0 [like Perl's <=> operator]
     */
     int32_t cmp(const BigInt& n, bool check_signs = true) const;

     /**
     * Test if the integer has an even value
     * @result true if the integer is even, false otherwise
     */
     bool is_even() const { return (get_bit(0) == 0); }

     /**
     * Test if the integer has an odd value
     * @result true if the integer is odd, false otherwise
     */
     bool is_odd()  const { return (get_bit(0) == 1); }

     /**
     * Test if the integer is not zero
     * @result true if the integer is non-zero, false otherwise
     */
     bool is_nonzero() const { return (!is_zero()); }

     /**
     * Test if the integer is zero
     * @result true if the integer is zero, false otherwise
     */
     bool is_zero() const
        {
        const size_t sw = sig_words();

        for(size_t i = 0; i != sw; ++i)
           if(m_reg[i])
              return false;
        return true;
        }

     /**
     * Set bit at specified position
     * @param n bit position to set
     */
     void set_bit(size_t n);

     /**
     * Clear bit at specified position
     * @param n bit position to clear
     */
     void clear_bit(size_t n);

     /**
     * Clear all but the lowest n bits
     * @param n amount of bits to keep
     */
     void mask_bits(size_t n)
        {
        if(n == 0) { clear(); return; }

        const size_t top_word = n / BOTAN_MP_WORD_BITS;
        const word mask = (static_cast<word>(1) << (n % BOTAN_MP_WORD_BITS)) - 1;

        if(top_word < size())
           {
           const size_t len = size() - (top_word + 1);
           if (len > 0)
              {
              clear_mem(&m_reg[top_word+1], len);
              }
           m_reg[top_word] &= mask;
           }
        }

     /**
     * Return bit value at specified position
     * @param n the bit offset to test
     * @result true, if the bit at position n is set, false otherwise
     */
     bool get_bit(size_t n) const
        {
        return ((word_at(n / BOTAN_MP_WORD_BITS) >> (n % BOTAN_MP_WORD_BITS)) & 1);
        }

     /**
     * Return (a maximum of) 32 bits of the complete value
     * @param offset the offset to start extracting
     * @param length amount of bits to extract (starting at offset)
     * @result the integer extracted from the register starting at
     * offset with specified length
     */
     uint32_t get_substring(size_t offset, size_t length) const;

     /**
     * Convert this value into a uint32_t, if it is in the range
     * [0 ... 2**32-1], or otherwise throw an exception.
     * @result the value as a uint32_t if conversion is possible
     */
     uint32_t to_u32bit() const;

     /**
     * @param n the offset to get a byte from
     * @result byte at offset n
     */
     uint8_t byte_at(size_t n) const
        {
        return get_byte(sizeof(word) - (n % sizeof(word)) - 1,
                        word_at(n / sizeof(word)));
        }

     /**
     * Return the word at a specified position of the internal register
     * @param n position in the register
     * @return value at position n
     */
     word word_at(size_t n) const
        { return ((n < size()) ? m_reg[n] : 0); }

     void set_word_at(size_t i, word w)
        {
        if(i >= m_reg.size())
           grow_to(i + 1);
        m_reg[i] = w;
        }

     /**
     * Tests if the sign of the integer is negative
     * @result true, iff the integer has a negative sign
     */
     bool is_negative() const { return (sign() == Negative); }

     /**
     * Tests if the sign of the integer is positive
     * @result true, iff the integer has a positive sign
     */
     bool is_positive() const { return (sign() == Positive); }

     /**
     * Return the sign of the integer
     * @result the sign of the integer
     */
     Sign sign() const { return (m_signedness); }

     /**
     * @result the opposite sign of the represented integer value
     */
     Sign reverse_sign() const
        {
        if(sign() == Positive)
           return Negative;
        return Positive;
        }

     /**
     * Flip the sign of this BigInt
     */
     void flip_sign()
        {
        set_sign(reverse_sign());
        }

     /**
     * Set sign of the integer
     * @param sign new Sign to set
     */
     void set_sign(Sign sign)
        {
        if(is_zero())
           m_signedness = Positive;
        else
           m_signedness = sign;
        }

     /**
     * @result absolute (positive) value of this
     */
     BigInt abs() const;

     /**
     * Give size of internal register
     * @result size of internal register in words
     */
     size_t size() const { return m_reg.size(); }

     /**
     * Return how many words we need to hold this value
     * @result significant words of the represented integer value
     */
     size_t sig_words() const
        {
        const word* x = m_reg.data();
        size_t sig = m_reg.size();

        while(sig && (x[sig-1] == 0))
           sig--;
        return sig;
        }

     /**
     * Give byte length of the integer
     * @result byte length of the represented integer value
     */
     size_t bytes() const;

     /**
     * Get the bit length of the integer
     * @result bit length of the represented integer value
     */
     size_t bits() const;

     /**
     * Return a mutable pointer to the register
     * @result a pointer to the start of the internal register
     */
     word* mutable_data() { return m_reg.data(); }

     /**
     * Return a const pointer to the register
     * @result a pointer to the start of the internal register
     */
     const word* data() const { return m_reg.data(); }

     secure_vector<word>& get_word_vector() { return m_reg; }
     const secure_vector<word>& get_word_vector() const { return m_reg; }

     /**
     * Increase internal register buffer to at least n words
     * @param n new size of register
     */
     void grow_to(size_t n);

     /**
     * Resize the vector to the minimum word size to hold the integer, or
     * min_size words, whichever is larger
     */
     void shrink_to_fit(size_t min_size = 0);

     /**
     * Fill BigInt with a random number with size of bitsize
     *
     * If \p set_high_bit is true, the highest bit will be set, which causes
     * the entropy to be \a bits-1. Otherwise the highest bit is randomly chosen
     * by the rng, causing the entropy to be \a bits.
     *
     * @param rng the random number generator to use
     * @param bitsize number of bits the created random value should have
     * @param set_high_bit if true, the highest bit is always set
     */
     void randomize(RandomNumberGenerator& rng, size_t bitsize, bool set_high_bit = true);

     /**
     * Store BigInt-value in a given byte array
     * @param buf destination byte array for the integer value
     */
     void binary_encode(uint8_t buf[]) const;

     /**
     * Read integer value from a byte array with given size
     * @param buf byte array buffer containing the integer
     * @param length size of buf
     */
     void binary_decode(const uint8_t buf[], size_t length);

     /**
     * Read integer value from a byte array (secure_vector<uint8_t>)
     * @param buf the array to load from
     */
     void binary_decode(const secure_vector<uint8_t>& buf)
        {
        binary_decode(buf.data(), buf.size());
        }

     /**
     * @param base the base to measure the size for
     * @return size of this integer in base base
     */
     size_t encoded_size(Base base = Binary) const;

     /**
     * Place the value into out, zero-padding up to size words
     * Throw if *this cannot be represented in size words
     */
     void encode_words(word out[], size_t size) const;

     /**
     * @param rng a random number generator
     * @param min the minimum value
     * @param max the maximum value
     * @return random integer in [min,max)
     */
     static BigInt random_integer(RandomNumberGenerator& rng,
                                  const BigInt& min,
                                  const BigInt& max);

     /**
     * Create a power of two
     * @param n the power of two to create
     * @return bigint representing 2^n
     */
     static BigInt power_of_2(size_t n)
        {
        BigInt b;
        b.set_bit(n);
        return b;
        }

     /**
     * Encode the integer value from a BigInt to a std::vector of bytes
     * @param n the BigInt to use as integer source
     * @param base number-base of resulting byte array representation
     * @result secure_vector of bytes containing the integer with given base
     */
     static std::vector<uint8_t> encode(const BigInt& n, Base base = Binary);

     /**
     * Encode the integer value from a BigInt to a secure_vector of bytes
     * @param n the BigInt to use as integer source
     * @param base number-base of resulting byte array representation
     * @result secure_vector of bytes containing the integer with given base
     */
     static secure_vector<uint8_t> encode_locked(const BigInt& n,
                                              Base base = Binary);

     /**
     * Encode the integer value from a BigInt to a byte array
     * @param buf destination byte array for the encoded integer
     * value with given base
     * @param n the BigInt to use as integer source
     * @param base number-base of resulting byte array representation
     */
     static void encode(uint8_t buf[], const BigInt& n, Base base = Binary);

     /**
     * Create a BigInt from an integer in a byte array
     * @param buf the binary value to load
     * @param length size of buf
     * @param base number-base of the integer in buf
     * @result BigInt representing the integer in the byte array
     */
     static BigInt decode(const uint8_t buf[], size_t length,
                          Base base = Binary);

     /**
     * Create a BigInt from an integer in a byte array
     * @param buf the binary value to load
     * @param base number-base of the integer in buf
     * @result BigInt representing the integer in the byte array
     */
     static BigInt decode(const secure_vector<uint8_t>& buf,
                          Base base = Binary)
        {
        return BigInt::decode(buf.data(), buf.size(), base);
        }

     /**
     * Create a BigInt from an integer in a byte array
     * @param buf the binary value to load
     * @param base number-base of the integer in buf
     * @result BigInt representing the integer in the byte array
     */
     static BigInt decode(const std::vector<uint8_t>& buf,
                          Base base = Binary)
        {
        return BigInt::decode(buf.data(), buf.size(), base);
        }

     /**
     * Encode a BigInt to a byte array according to IEEE 1363
     * @param n the BigInt to encode
     * @param bytes the length of the resulting secure_vector<uint8_t>
     * @result a secure_vector<uint8_t> containing the encoded BigInt
     */
     static secure_vector<uint8_t> encode_1363(const BigInt& n, size_t bytes);

     static void encode_1363(uint8_t out[], size_t bytes, const BigInt& n);

     /**
     * Encode two BigInt to a byte array according to IEEE 1363
     * @param n1 the first BigInt to encode
     * @param n2 the second BigInt to encode
     * @param bytes the length of the encoding of each single BigInt
     * @result a secure_vector<uint8_t> containing the concatenation of the two encoded BigInt
     */
     static secure_vector<uint8_t> encode_fixed_length_int_pair(const BigInt& n1, const BigInt& n2, size_t bytes);

     /**
     * Set output = vec[idx].m_reg in constant time
     * All words of vec must have the same size
     */
     static void const_time_lookup(
        secure_vector<word>& output,
        const std::vector<BigInt>& vec,
        size_t idx);

   private:
      secure_vector<word> m_reg;
      Sign m_signedness = Positive;
   };

/*
* Arithmetic Operators
*/
BigInt BOTAN_PUBLIC_API(2,0) operator+(const BigInt& x, const BigInt& y);
BigInt BOTAN_PUBLIC_API(2,0) operator-(const BigInt& x, const BigInt& y);
BigInt BOTAN_PUBLIC_API(2,0) operator*(const BigInt& x, const BigInt& y);
BigInt BOTAN_PUBLIC_API(2,0) operator/(const BigInt& x, const BigInt& d);
BigInt BOTAN_PUBLIC_API(2,0) operator%(const BigInt& x, const BigInt& m);
word   BOTAN_PUBLIC_API(2,0) operator%(const BigInt& x, word m);
BigInt BOTAN_PUBLIC_API(2,0) operator<<(const BigInt& x, size_t n);
BigInt BOTAN_PUBLIC_API(2,0) operator>>(const BigInt& x, size_t n);

/*
* Comparison Operators
*/
inline bool operator==(const BigInt& a, const BigInt& b)
   { return (a.cmp(b) == 0); }
inline bool operator!=(const BigInt& a, const BigInt& b)
   { return (a.cmp(b) != 0); }
inline bool operator<=(const BigInt& a, const BigInt& b)
   { return (a.cmp(b) <= 0); }
inline bool operator>=(const BigInt& a, const BigInt& b)
   { return (a.cmp(b) >= 0); }
inline bool operator<(const BigInt& a, const BigInt& b)
   { return (a.cmp(b) < 0); }
inline bool operator>(const BigInt& a, const BigInt& b)
   { return (a.cmp(b) > 0); }

/*
* I/O Operators
*/
BOTAN_PUBLIC_API(2,0) std::ostream& operator<<(std::ostream&, const BigInt&);
BOTAN_PUBLIC_API(2,0) std::istream& operator>>(std::istream&, BigInt&);

}

namespace std {

template<>
inline void swap<Botan::BigInt>(Botan::BigInt& x, Botan::BigInt& y)
   {
   x.swap(y);
   }

}

#endif