playfair.cpp

三种密码学中简单的加密算法：Playfair

#include <iostream.h>
#include <string.h>
void main()
{
	char text[200],key[50],matrix[5][5],code[200],ch,a,b,c,d;
	char abc[27]="abcdefghijklmnopqrstuvwxyz";
	int l1,l2,i,j,k,n,p1=1,p2=1,p3,s,t,u,v;
    cout<<"Please input the clear text (with lowercase letters):"<<endl;
    cin>>text;
	cout<<"Please input the cryptographic key (with lowercase letters):"<<endl;
	cin>>key;
	l1=strlen(text);
	l2=strlen(key);
	for (i=l2;i<l2+26;i++)
		key[i]=abc[i-l2];
	l2=l2+26;
	for (i=0;i<l1&&p1!=0;i++)
		if (int(text[i])-97<0 ||int(text[i])-97>25)
			p1=0;
    for (i=0;i<l2-26&&p1!=0;i++)
	{
		if (int(key[i])-97<0||int(key[i])-97>25)
			p1=0;
		if (key[i]=='j')
			p2=0;
	}
	if (p2==0)
	{
		for (i=0;i<l2;i++)
			if (key[i]=='i')
				key[i]='j';
	}
	else
	{
		for (i=0;i<l2;i++)
			if (key[i]=='j')
				key[i]='i';
	}
	if (p1==0)
		cout<<"Error!"<<endl;
	else
	{
		matrix[0][0]=key[0];
		n=1;
		for (i=1;i<l2&&n<25;i++)
		{
			ch=key[i];
			p3=1;
			for (j=0;j<n/5;j++)
				for (k=0;k<5;k++)
					if (ch==matrix[j][k])
						p3=0;
		    for (j=n/5;j<n/5+1;j++)
				for (k=0;k<n%5;k++)
					if (ch==matrix[j][k])
						p3=0;
			if (p3!=0)
			{
				matrix[n/5][n%5]=ch;
				n++;
			}
		}
		cout<<"The matrix is:"<<endl;
		for (i=0;i<5;i++)
		{
			for (j=0;j<5;j++)
				cout<<matrix[i][j]<<" ";
			cout<<endl;
		}
		cout<<"The cryptograph is:"<<endl;
		for (i=0;i<l1;i++)
		{
			a=text[i];
			if (i+1==l1)
				b='q';
			else
			{
				if (text[i+1]!=a)
				{
					b=text[i+1];
					i++;
				}
				else
					text[i+1]='q';
			}
			for (j=0;j<5;j++)
				for (k=0;k<5;k++)
				{
					if (a==matrix[j][k])
					{
						s=j;
						t=k;
					}
					if (b==matrix[j][k])
					{
						u=j;
						v=k;
					}
				}
			if (s==u)
			{
				c=matrix[s][(t+1)%5];
				d=matrix[u][(v+1)%5];
			}
			else
			{
				if (t==v)
				{
					c=matrix[(s+1)%5][t];
				    d=matrix[(u+1)%5][v];
				}
				else
				{
					c=matrix[s][v];
					d=matrix[u][t];
				}
			}
			cout<<c<<d;
		}
		cout<<endl;
	}
}