物联网安全技术——凯撒密码

#include<iostream>
#include<string>
#include<vector>
#include<cctype>
#include<fstream>
#include<sstream>
using namespace std;
vector<string> EncryptedMessage;
vector<string> word;
vector<vector<string>> dic;

string encryption(const string message,int i) {
	string m = message;
	for (auto j = 0; j < m.length(); j++) {
		if (isalpha(m[j])) {
			if (isupper(m[j])) {
				m[j] = (m[j] - 'A' + i) % 26 + 'A';
			}
			else {
				m[j] = (m[j] - 'a' + i) % 26 + 'a';
			}
		}
	}
	//cout << message << endl;
	return m;
}

string decryption(string m,int i) {
	string c = m;
	for (auto j = 0; j < m.length(); j++) {
		if (isalpha(m[j])) {
			if (isupper(m[j])) {
				c[j] = (m[j] - 'A' + 26 - i) % 26 + 'A';
			}
			else {
				c[j] = (m[j] - 'a' + 26 - i) % 26 + 'a';
			}
		}
	}
	
	return c;
}

void readFile() {
	string path = "《英汉汉英词典》.txt";
	fstream file;
	string ReadMessage;
	file.open(path);
	string s;
	int count = 0;
	if (file.is_open()) {
		cout << "文件已打开" << endl;
		while (getline(file, s))
		{
			int tt = tolower(s[0]) - 'a';
			for (auto i = 0; i < s.length(); i++) {
				if (isspace(s[i])) {
					int index = i;
					s = s.substr(0, index);
					s[0] = tolower(s[0]);
					word.push_back(s);
					//cout << s << " " << s.length() << endl;
					/*if (tt != s[0] - 'a') {
						dic.push_back(word);
						word.clear();
						word.push_back(s);
						count++;
					}
					else {
						word.push_back(s);
						count++;
					}*/
					//cout << s << endl;
				}
			}
		}
	/*	cout << count << endl;*/
	}

}

vector<string> splitWord(string m) {
	vector<string> vec;
	int index1 = 0, index2;
	string word;
	for (auto i = 0; i < m.length(); i++) {
		if (m[i] == ' '||ispunct(m[i])||i==m.length()-1) {
			if (i == m.length() - 1) {
				index2 = i + 1;
			}
			else {
				index2 = i;
			}
			word = m.substr(index1, index2 - index1);
			index1 = index2+1;
			word[0] = tolower(word[0]);
			vec.push_back(word);
		}
	}
	return vec;
}

int searchWord(string w) {
	for (auto i = 0; i < word.size(); i++) {
		if (w == word[i]) {
			return 1;
		}
		
	}
	return 0;
}


double getRate(string m) {
	double count = 0.0;
	vector<string> vec = splitWord(m);
	for (auto i = 0; i < vec.size(); i++) {
		//cout << vec[i] << endl;
		if (searchWord(vec[i])) {
			count++;
		}
	}
	double rate = count / vec.size();
	return rate;
}


int main() {
	readFile();
	double rate = 0;
	string correctMessage;
	string message = "Liu Weifu, meet me at the party"; //明文
	int key = 5;
	string m = encryption(message, key);
	cout <<"密文 "<< m << endl;
	for (auto i = 1; i < 26; i++) {	
		EncryptedMessage.push_back(decryption(m, i));
	}
	for (auto k = 0; k < EncryptedMessage.size(); k++) {
		cout << "key = " << k+1 << " ";
		cout << EncryptedMessage[k] << " ";
		cout << getRate(EncryptedMessage[k]) << endl;
		if (rate < getRate(EncryptedMessage[k])) {
			rate = getRate(EncryptedMessage[k]);
			correctMessage = EncryptedMessage[k];
		}
	}
	cout << "明文为：" << correctMessage << endl;
	system("pause");
	return 0;
}