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C语言设计一个简单的加密解密程序如旦饥下：
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加密程序代码：
#include孝迟虚stdio.h
main()
{
char c,filename[20];
FILE *fp1,*fp2;
printf("请输入待加密的文件名巧燃:\n");
scanf("%s",filename);
fp1=fopen(filename,"r");
fp2=fopen("miwen.txt","w");
do
{
c=fgetc(fp1);
if(c=32c=126)
{
c=c-32;
c=126-c;
}
if(c!=-1)
fprintf(fp2,"%c",c);
}
while(c!=-1);
}
解密程序代码：
#includestdio.h
#includestring.h
main()
{
char c,filename[20];
char yanzhengma[20];
FILE *fp1,*fp2;
printf("请输入待解密文件名:\n");
scanf("%s",filename);
printf("请输入验证码:\n");
scanf("%s",yanzhengma);
if(strcmp(yanzhengma,"shan")==0)
{
fp1=fopen(filename,"r");
fp2=fopen("yuanwen.txt","w");
do
{
c=fgetc(fp1);
if(c=32c=126)
{
c=126-c;
c=32+c;
}
if(c!=-1)
fprintf(fp2,"%c",c);
}
while(c!=-1);
}
else
{
printf("验证码错误！请重新输入:\n");
scanf("%s",filename);
}
}
char* encode(const char* str)
{
int i, s;
s = 0;
for(i = 0; str[i]; i++) s += str[i] * str[i];
for(i = 0; str[i]; i++) {
if(str[i] = 'a' str[i] = 'z') {
str[i] = (str[i] + s) % 128;
}
}
return str;
}
不激皮能准确地恢明亩差耐岩复
1、主要就是调用库函数，MD5加密说到底也是函数计算，没有什么思路的问题，了解md5的发明算法，本质是一个数学问题。
2、例程：
#ifndef MD5_H
#define MD5_H
typedef struct
{
unsigned int count[2];
unsigned int state[4];
unsigned char buffer[64];
}MD5_CTX;
#define F(x,y,z) ((x y) | (~x z))
#define G(x,y,z) ((x z) | (y ~z))
#define H(x,y,z) (x^y^z)
#define I(x,y,z) (y ^ (x | ~z))
#define ROTATE_LEFT(x,n) ((x n) | (x (32-n)))
#define FF(a,b,c,d,x,s,ac) \
{ \
a += F(b,c,d) + x + ac; \
a = ROTATE_LEFT(a,s); \
a += b; \
}
#define GG(a,b,c,d,x,s,ac) \
{ \
稿亏 a += G(b,c,d) + x + ac; \
a = ROTATE_LEFT(a,s); \
a += b; 袜岩\
}
#define HH(a,b,c,d,x,s,ac) \
{ \
a += H(b,c,d) + x + ac; \
a = ROTATE_LEFT(a,s); \
a += b; \
}
#define II(a,b,c,d,x,s,ac) \
{ \
a += I(b,c,d) + x + ac; \
a = ROTATE_LEFT(a,s); \
a += b; \
}
void MD5Init(MD5_CTX *context);
void MD5Update(MD5_CTX *context,unsigned char *input,unsigned int inputlen);
void MD5Final(MD5_CTX *context,unsigned char digest[16]);
void MD5Transform(unsigned int state[4],unsigned char block[64]);
void MD5Encode(unsigned char *output,unsigned 告敬御int *input,unsigned int len);
void MD5Decode(unsigned int *output,unsigned char *input,unsigned int len);
#endif
源文件md5.c
#include memory.h
#include "md5.h"
unsigned char PADDING[]={0x80,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
void MD5Init(MD5_CTX *context)
{
context-count[0] = 0;
context-count[1] = 0;
context-state[0] = 0x67452301;
context-state[1] = 0xEFCDAB89;
context-state[2] = 0x98BADCFE;
context-state[3] = 0x10325476;
}
void MD5Update(MD5_CTX *context,unsigned char *input,unsigned int inputlen)
{
unsigned int i = 0,index = 0,partlen = 0;
index = (context-count[0] 3) 0x3F;
partlen = 64 - index;
context-count[0] += inputlen 3;
if(context-count[0] (inputlen 3))
context-count[1]++;
context-count[1] += inputlen 29;
if(inputlen = partlen)
{
memcpy(context-buffer[index],input,partlen);
MD5Transform(context-state,context-buffer);
for(i = partlen;i+64 = inputlen;i+=64)
MD5Transform(context-state,input[i]);
index = 0;
}
else
{
i = 0;
}
memcpy(context-buffer[index],input[i],inputlen-i);
}
void MD5Final(MD5_CTX *context,unsigned char digest[16])
{
unsigned int index = 0,padlen = 0;
unsigned char bits[8];
index = (context-count[0] 3) 0x3F;
padlen = (index 56)?(56-index):(120-index);
MD5Encode(bits,context-count,8);
MD5Update(context,PADDING,padlen);
MD5Update(context,bits,8);
MD5Encode(digest,context-state,16);
}
void MD5Encode(unsigned char *output,unsigned int *input,unsigned int len)
{
unsigned int i = 0,j = 0;
while(j len)
{
output[j] = input[i] 0xFF;
output[j+1] = (input[i] 8) 0xFF;
output[j+2] = (input[i] 16) 0xFF;
output[j+3] = (input[i] 24) 0xFF;
i++;
j+=4;
}
}
void MD5Decode(unsigned int *output,unsigned char *input,unsigned int len)
{
unsigned int i = 0,j = 0;
while(j len)
{
output[i] = (input[j]) |
(input[j+1] 8) |
(input[j+2] 16) |
(input[j+3] 24);
i++;
j+=4;
}
}
void MD5Transform(unsigned int state[4],unsigned char block[64])
{
unsigned int a = state[0];
unsigned int b = state[1];
unsigned int c = state[2];
unsigned int d = state[3];
unsigned int x[64];
MD5Decode(x,block,64);
FF(a, b, c, d, x[ 0], 7, 0xd76aa478); /* 1 */
FF(d, a, b, c, x[ 1], 12, 0xe8c7b756); /* 2 */
FF(c, d, a, b, x[ 2], 17, 0x242070db); /* 3 */
FF(b, c, d, a, x[ 3], 22, 0xc1bdceee); /* 4 */
FF(a, b, c, d, x[ 4], 7, 0xf57c0faf); /* 5 */
FF(d, a, b, c, x[ 5], 12, 0x4787c62a); /* 6 */
FF(c, d, a, b, x[ 6], 17, 0xa8304613); /* 7 */
FF(b, c, d, a, x[ 7], 22, 0xfd469501); /* 8 */
FF(a, b, c, d, x[ 8], 7, 0x698098d8); /* 9 */
FF(d, a, b, c, x[ 9], 12, 0x8b44f7af); /* 10 */
FF(c, d, a, b, x[10], 17, 0xffff5bb1); /* 11 */
FF(b, c, d, a, x[11], 22, 0x895cd7be); /* 12 */
FF(a, b, c, d, x[12], 7, 0x6b901122); /* 13 */
FF(d, a, b, c, x[13], 12, 0xfd987193); /* 14 */
FF(c, d, a, b, x[14], 17, 0xa679438e); /* 15 */
FF(b, c, d, a, x[15], 22, 0x49b40821); /* 16 */
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