C语言实现：凯撒密码算法（加密 与 解密）

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最近在读《图解密码技术(日)结城浩(著).pdf》，想着为后续增加更深刻的印象与密码学算法的理解

#include <stdio.h>
#include <memory.h>
#include <intrin.h>

char alphabet[26] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i',
				     'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 
				     's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};

char decTable[26] = {0x00};


int CaesarPassword_ENC(char *dataBuf, char *passwordBuf, int dataLen)
{
	int i, j;

	for (i=0; i<dataLen; i++)
	{
		for (j=0; j<26; j++)
		{
			if (dataBuf[i] == alphabet[j])
			{
				passwordBuf[i] = decTable[j];
				break;
			}
		}
	}
	return 0;
}

int CaesarPassword_DEC(char *passwordBuf, char *dataBuf, int dataLen)
{
	int i, j;

	for (i=0; i<dataLen; i++)
	{
		for (j=0; j<26; j++)
		{
			if (passwordBuf[i] == decTable[j])
			{
				dataBuf[i] = alphabet[j];
				break;
			}
		}
	}
	return 0;
}

int GenerateDecTable(char *dest, char *src, int step)
{
	int i, j;

	for (i=0,j=0; i<26; i++)
	{
		j=i+step;
		
		if (j>=26)
			j-=26;

		decTable[i] = alphabet[j];
	}

	return 0;
}

int main(void)
{
	int key;
	char data[500];
	char encData[500];
	char decData[500];

	while(1)
	{
		key = 0;
		memset(&decTable, 0, sizeof(decTable));
		memset(&data, 0, sizeof(data));
		memset(&encData, 0, sizeof(encData));
		memset(&decData, 0, sizeof(decData));

		printf("-----------------------------------------------------\n");
		// Negotiate key 
		printf("please input key:\n");
		scanf("%d", &key);
		GenerateDecTable(decTable, alphabet, key);

		// get data
		printf("\nplease input data:\n");
		scanf("%s", &data);

		// Calculation of cipher
		CaesarPassword_ENC(data, encData, strlen(data));
		printf("\nout ENC Data:\n%s\n", encData);

		// Calculate clear
		CaesarPassword_DEC(encData, decData, strlen(encData));
		printf("\nout DEC Data:\n%s\n\n", decData);

		if (memcmp(data, decData, strlen(data)))
			printf("\n\nError\n\n");
	}
	
	return 0;
}