C语言实现：凯撒密码算法（加密 、解密 与 破译）

最近在读《图解密码技术(日)结城浩(著).pdf》，想着 打好基础 与 增加对密码学算法的理解

#include 
#include 
#include 

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=26)
			j-=26;

		dest[i] = src[j];
	}

	return 0;
}

int CaesarPassword_deCode(char *buf)
{
	int i;
	char deCode[26];
	char tempBuf[500];

	for (i=0; i<26; i++)
	{
		memset(&tempBuf, 0, sizeof(tempBuf));

		GenerateDecTable(deCode, alphabet, i);

		// Calculate clear
		CaesarPassword_DEC(buf, tempBuf, deCode, strlen(buf));
		printf("\nout deCode(%d):\n%s\n\n", i, tempBuf);
	}
	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, decTable, strlen(encData));
		printf("\nout DEC Data:\n%s\n\n", decData);

		if (memcmp(data, decData, strlen(data)) != 0)
			printf("\n\nError\n\n");

		CaesarPassword_deCode(encData);
	}
	
	return 0;
}

演示结果

可见只需 26 次解密，就一定能有一次成功，机密性太脆弱。

---

please input key:
3

please input data:
saji

out ENC Data:
vdml

out DEC Data:
saji

out deCode(0):
vdml

out deCode(1):
uclk

out deCode(2):
tbkj

out deCode(3):
saji

out deCode(4):
rzih

out deCode(5):
qyhg

out deCode(6):
pxgf

out deCode(7):
owfe

out deCode(8):
nved

out deCode(9):
mudc

out deCode(10):
ltcb

out deCode(11):
ksba

out deCode(12):
jraz

out deCode(13):
iqzy

out deCode(14):
hpyx

out deCode(15):
goxw

out deCode(16):
fnwv

out deCode(17):
emvu

out deCode(18):
dlut

out deCode(19):
ckts

out deCode(20):
bjsr

out deCode(21):
airq

out deCode(22):
zhqp

out deCode(23):
ygpo

out deCode(24):
xfon

out deCode(25):
wenm

---

please input key: