简单加密--C++实现单表置换、双表置换加密解密

        大一时学习C++，觉得密码学的一些东西挺有意思，因此为了练习c++，实现了一些简单的加密解密过程（非专业，目的仅仅是当时为了熟悉c++）。

1.实现一个简单的单表置换加密与解密功能。

单表置换加密即让原符号与新符号一一对应，进而对用原符号组成的符号串进行加密。 

下面实现了让abcdefghijklmnopqrstuvwxyz中的元素依次对应qazwsxedcrfvtgbyhnujmikolp中的元素，进而加密与解密

输入：abcde

加密后输出：qazws

1. 加密函数
2. 解密函数
3. 主函数

2.实现一个双表置换的加密解密功能。

双表置换加密即让一串原文与两张表进行映射，并按照某种规律进行加密。

原符号：Abcdefghijklmnopqrstuvwxyz

对应的置换表：

（1）Qwertyuiopasdfghjklzxcvbnm(句子中的某一字母第1.3.5……次出现用该加密方式)

（2）Lkjhgfdsaqwertyuiopmnbzxcv（句子中的某一字母第2.4.6……次出现用该加密方式）

1. 加密方式1函数
2. 加密方式2函数
3. 选择加密方式函数
4. 实现加密函数
5. 对应解密方式一函数
6. 对应解密方式二函数
7. 解密函数
8. 主函数

输入：AAbbcc

加密后输出：QLwkej

单表加密代码

//单表置换密码
、
//加密
int first_change(string& sentence)
{
	int location;
	string key1 = "qazwsxedcrfvtgbyhnujmikolp";
	string alphabet = "abcdefghijklmnopqrstuvwxyz";//对应的置换单表，可进行修改
	for (int i = 0;i < sentence.length();i++)
	{	
		if (sentence[i] != ' ')
		{
			location = alphabet.find_first_of(sentence[i]);
			sentence[i] = key1[location];
		}
	}
	return 1;

}


//解密

int first_decode(string& sentence)
{
	int location;
	string key1 = "qazwsxedcrfvtgbyhnujmikolp";
	string alphabet = "abcdefghijklmnopqrstuvwxyz";
	for (int i = 0;i < sentence.length();i++)
	{
		if (sentence[i] != ' ')
		{
			location = key1.find_first_of(sentence[i]);
			sentence[i] = alphabet[location];
		}
	}
	return 1;
}
//单表置换密码

int main()
{
	string sentence;
	cout << "please input what you want to encrypt:" << endl;
	getline(cin, sentence);
	first_change(sentence);
	cout << "加密后" << endl;
	cout << sentence << endl;
	first_decode(sentence);
	cout << "解密后" << endl;
	cout << sentence << endl;

}

运行结果：

双表加密代码

//双表置换加密

//第一种加密
int first_change( char &letter)
{
	int location;
	string key1 = "qwertyuiopasdfghjklzxcvbnm";
	string alphabet = "abcdefghijklmnopqrstuvwxyz";
	if (letter!= ' ')
	{
		location = alphabet.find_first_of(letter);
		letter = key1[location];
	}
	return 1;
}

//第二种加密
int second_change(char& letter)
{
	int location;
	string key2 = "lkjhgfdsaqwertyuiopmnbzxcv";
	string alphabet = "abcdefghijklmnopqrstuvwxyz";
	if (letter != ' ')
	{
		location = alphabet.find_first_of(letter);
		letter = key2[location];
	}
	return 1;
}
//加密时：判断该字母第几次出现在句子当中
int judeg_encryption(const char letter)
{
	static map letter_nums
	{
		{'a',0},{'b',0},{'c',0},{'d',0},{'e',0},{'f',0},
		{'g',0},{'h',0},{'i',0},{'g',0},{'k',0},{'l',0},
		{'m',0},{'n',0},{'o',0},{'p',0},{'q',0},{'r',0},
		{'s',0},{'t',0},{'u',0},{'v',0},{'w',0},{'x',0},
		{'y',0},{'z',0}
	};
	if (letter != ' ')
	{
		letter_nums[letter]++;
	}

	 return letter_nums[letter]%2;
	 //若返回值为1，对应第一次加密方法
	 //若返回值为二，对应第二次加密方法
}

//加密
string encryption(string& sentence,vector &record )
{
	char letter;
	int option;//接受选择判断函数的返回值
	for (int i = 0;i < sentence.length();i++)
	{
		if (sentence[i] != ' ')
		{
			letter = sentence[i];
			option = judeg_encryption(letter);
			if (option ==1)
			{
				first_change(letter);
				sentence[i] = letter;
				record.push_back(1);
				
			}
			if (option == 0)
			{
				second_change(letter);
				sentence[i] = letter;
				record.push_back(0);
			}
		}
	}
	return sentence;
}

//重载第一种解密
int first_decode(char& letter)
{
	int location;
	string key1 = "qwertyuiopasdfghjklzxcvbnm";
	string alphabet = "abcdefghijklmnopqrstuvwxyz";
	if (letter != ' ')
	{
		location = key1.find_first_of(letter);
		letter = alphabet[location];
	}
	return 1;
}
//第二种解密
int second_decode(char& letter)
{
	int location;
	string key2 = "lkjhgfdsaqwertyuiopmnbzxcv";
	string alphabet = "abcdefghijklmnopqrstuvwxyz";
	if (letter != ' ')
	{
		location = key2.find_first_of(letter);
		letter = alphabet[location];
	}
	return 1;
}


string decode(string& sentence, const vector record)
{
	char letter;
	int j = 0;
	for (int i = 0;i < sentence.length();i++)
	{
		if (sentence[i] != ' ')
		{
			if (record[j] == 1)
			{	
				letter = sentence[i];
				first_decode(letter);
				sentence[i] = letter;
			}
			if (record[j] == 0)
			{
				letter = sentence[i];
				second_decode(letter);
				sentence[i] = letter;
			}
			j++;
		}
	}
	return sentence;
}

//双表置换加密


int main()
{	
	static vector record;
	
	string sentence;
	cout << "please input what you want to encrypt:" << endl;
	getline(cin, sentence);
	encryption(sentence,record);
	cout << "加密后" << endl;
	cout << sentence << endl;
	cout << "解密后" << endl;
	cout << decode(sentence, record);
}

运行结果：