密码学习题--仿射变换cpp代码实现

密码学习题–仿射变换cpp代码实现

#include 
using namespace std;
int mod(int num, int m)
{
	while(num<0) num+=m;
    int tmp=num/m;
    return num-tmp*m;
}  //求模
int get_reverse(int num, int m)
{
    for(int i=1; i<=m; i++)
    {
        if(mod(num*i, m)==1) return i;
    }
    return -1;
}  //求逆
void get_int_Arr(char word[], int num[])
{
    for(int i=0; word[i]!=0; i++)
    {
        num[i]=mod(word[i]-'A'+1, 26);
    }
}
int get_TotalNumber(char word[])
{
    int cnt=0;
    for(int i=0; word[i]!=0; i++) cnt++;
    return cnt;
}
void Code(char word[], int a, int b)
{
    int* num=new int[get_TotalNumber(word)];

	for(int i=0; i<=get_TotalNumber(word)-1; i++)
	{
		num[i]=word[i]-'a';
		int c=mod(a*num[i]+b, 26);
		char tmp=c+'a';
		cout<<tmp<<' ';
	}

	delete[] num;
}  //编码
void Decode(char word[], int a, int b)
{
	int* num=new int[get_TotalNumber(word)];
	int r=get_reverse(a, 26);

	for(int i=0; i<=get_TotalNumber(word)-1; i++)
	{
		num[i]=word[i]-'a';
		int m=mod(r*(num[i]-b), 26);
		char tmp=m+'a';
		cout<<tmp<<' ';
	}

	delete[] num;
}  //解码
void main()
{
	char word4[]="thenationalsecurityagency";
	Code(word4, 11, 23);  //ywpkxyhvkxonptjchybxlpktb
	cout<<endl;
	char word5[]="edsgickxhuklzveqzvkxwkzukvcuh";
	Decode(word5, 9, 10);
}