密碼學（playfair）

    

playfair.h

#ifndef PLAYFAIR_H
#define PLAYFAIR_H

#include <string>
#include <utility>
using namespace std;

class PlayFair
{
 private:
  char m_ch;
  int m_position;
  string m_key;
  string m_letter;
  void ToLower(string &str);
  bool emptyKey() const;
  void keySameLetter();
  void deleteLetter();
  void addLetter();
  void initialize();
  void changeMessage(string &str);
  bool sameRow(char lch, char rch, pair<int,int> &p) const;
  bool sameColumn(char lch, char rch, pair<int, int> &p) const;
  bool isRight(int po);
  bool isBottom(int po);
  void sameRowInsert(pair<int,int> &p, string &str);
  void sameColumnInsert(pair<int, int> &p, string &str);
  void nonSameInsert(pair<int, int> &p, string &str);
 public:
  explicit PlayFair(){};
  explicit PlayFair(const string &str);
  explicit PlayFair(const char *ch);
  PlayFair& operator = (const PlayFair &p);
  bool operator ==(const PlayFair &p);
  bool operator !=(const PlayFair &p);
  string encrypt(string str);

  void setKey(string &key);
  void setKey(char *ch);
};
#endif

pffun.cpp

#include <iostream>
#include <cctype>
#include "playfair.h"

PlayFair::PlayFair(const string &str):m_key(str)
{
 initialize();
}

PlayFair::PlayFair(const char *ch):m_key(ch)
{
 initialize();
}

void PlayFair::ToLower(string &str)
{
 string::iterator ite = str.begin();

 for (; ite != str.end(); ++ite)
 {
  if (isupper(*ite))
   *ite = tolower(*ite);
 }
}

bool PlayFair::emptyKey() const
{
 return m_key.empty();
}

void PlayFair::keySameLetter()
{
 if (!emptyKey())
 {
  string::iterator fite, site;
  fite = m_letter.begin();

  for (int i = 0; i < m_letter.size(); ++i)
  {
   fite = m_letter.begin() + i;
   site = fite + 1;

   for (int j = i + 1; j < m_letter.size(); ++j)
   {
    if (*fite != *site)
     ++site;
    else
    {
     site = m_letter.erase(site);
     fite = site - 1;
    }
   }
  }
 }

}

void PlayFair::deleteLetter()
{
 string::iterator ite = m_key.begin();

 for (; ite != m_key.end(); ++ite)
 {
  m_letter[*ite-97] = ' ';
 }
}

void PlayFair::addLetter()
{
 if (!emptyKey())
 {
  m_position = m_key.size();

  string::iterator ite = m_letter.begin();

  for (; ite != m_letter.end(); ++ite)
  {
   if (*ite != ' ')
    m_key.insert(m_key.end(), *ite);
  }
  m_ch = m_key[m_position];
  m_key.erase(&(m_key[m_position]));
 }

}

void PlayFair::initialize()
{
 m_letter = "abcdefghijklmnopqrstuvwxyz";
 ToLower(m_key);
 keySameLetter();
 deleteLetter();
 addLetter();
}

bool PlayFair::operator ==(const PlayFair &p) //左運算元不可以是常對象
{
 return (m_key == p.m_key);
}

bool PlayFair::operator != (const PlayFair &p)
{
 return !(m_key == p.m_key);
}
PlayFair& PlayFair::operator =(const PlayFair &p)
{
 if (*this == p)
  return *this;
 else
 {
  string::const_iterator ite = p.m_key.begin();

  for (; ite != p.m_key.end(); ++ite)
   m_key.insert(m_key.end(), *ite);
 }
 
 return *this;
}

void PlayFair::changeMessage(string &str)
{
 string::iterator fite, site;
 fite = str.begin();
 site = fite + 1;

 for (; fite != str.end() && site != str.end();)
 {
  if (*fite == *site)
  {
   if (*site == 'z')
    site = str.insert(site, 'a');
   else
    site = str.insert(site, *site+1);

   fite = site + 1;
   site = fite + 1;
  }

  else
  {
   ++fite;
   ++site;
  }
 }

 if (!str.empty() && str.size() % 2)
 {
  if (*(str.end() - 1) == 'z')
   str.insert(str.end(), 'a');
  else
   str.insert(str.end(), *(str.end()-1)+1);
 }
}

string PlayFair::encrypt(string str)
{
 if (!emptyKey())
 {
  string result;
  ToLower(str);
  changeMessage(str);
  
  pair<int, int> po;
  string::iterator fite, site;
  fite = str.begin();

  for (; fite != str.end(); fite += 2)
  {
   site = fite + 1;
   if (sameRow(*fite, *site, po))
    sameRowInsert(po, result);

   else
   {
    if (sameColumn(*fite, *site, po))
     sameColumnInsert(po, result);

    else
     nonSameInsert(po, result);
   }
  }
  return result;
 }
 else
  return "";
 
}

bool PlayFair::sameRow(char lch, char rch, pair<int,int> &p) const
{
 p.first = m_key.find(lch);
 if (p.first == string::npos)
  p.first = m_position;

 p.second = m_key.find(rch);
 if (p.second == string::npos)
  p.second = m_position;

 if (p.first / 5 == p.second / 5)
  return true;
 else
  return false;
}

bool PlayFair::sameColumn(char lch, char rch, pair<int, int> &p) const
{
 p.first = m_key.find(lch);
 if (p.first == string::npos)
  p.first = m_position;

 p.second = m_key.find(rch);
 if (p.second == string::npos)
  p.second = m_position;

 if (p.first % 5 == p.second % 5)
  return true;
 else
  return false;
}

inline bool PlayFair::isRight(int po)
{
 return (po % 5 == 4);
}

inline bool PlayFair::isBottom(int po)
{
 return (po / 5 == 4);
}

void PlayFair::sameRowInsert(pair<int,int> &p, string &str)
{
 if (isRight(p.first))
  str.insert(str.end(), m_key[p.first-4]);
 else
  str.insert(str.end(), m_key[p.first+1]);

 if (isRight(p.second))
  str.insert(str.end(), m_key[p.second-4]);
 else
  str.insert(str.end(), m_key[p.second+1]);
}

void PlayFair::sameColumnInsert(pair<int, int> &p, string &str)
{
 if (isBottom(p.first))
  str.insert(str.end(), m_key[p.first-20]);
 else
  str.insert(str.end(), m_key[p.first+5]);

 if (isBottom(p.second))
  str.insert(str.end(), m_key[p.second-20]);
 else
  str.insert(str.end(), m_key[p.second+5]);
}

inline void PlayFair::nonSameInsert(pair<int, int> &p, string &str)
{
 str.insert(str.end(), m_key[p.first/5*5+p.second%5]);
 str.insert(str.end(), m_key[p.second/5*5+p.first%5]);
}

void PlayFair::setKey(string &str)
{
 m_key = str;
 initialize();
}

void PlayFair::setKey(char *ch)
{
 m_key = ch;
 initialize();
}