加密程序代码：
#include<stdio.h>
main()
{
char
c,filename[20]
FILE
*fp1,*fp2
scanf("%s",filename)
fp1=fopen(filename,"r")
fp2=fopen("miwen.txt","w")
do
{
c=fgetc(fp1)
if(c>=32&&c<=126)
{
c=c-32
c=126-c
}
if(c!=-1)
fprintf(fp2,"%c",c)
}
while(c!=-1)
}
解密程序代码：
#include<stdio.h>
#include<string.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>=32&&c<=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)
}
}
根据你的需要，修改了之前的代码。
#include <stdio.h>#include <string.h>
#include <stdlib.h>
#include <time.h>
const unsigned int MAX_KEY_LENGTH = 1000
int encode(char const *datafile, char const *keyfill)
int decode(char const *datafile, char const *keyfile)
int loadKey(char const *keyfile, int *keys, unsigned int size)
int saveKey(char const *keyfile, int *keys, unsigned int size)
int generateKey(int *keys, unsigned int size)
int main(int argc, char const *argv[])
{
char datafile[] = "encrypted.txt"
char keyfile[] = "key.txt"
int retcode, choice, loop = 1
char ch[5] = {'\0'}
while(1)
{
printf("1. Encryption.\n")
printf("2. Decryption.\n")
printf("3. Exit.\n")
printf("Selection (1,2,3):")
fgets(ch, sizeof(ch), stdin)
sscanf(ch, "%d", &choice)
switch(choice)
{
case 1:
retcode = encode(datafile, keyfile)
if (retcode != 0) printf("error, %d\0", retcode)
break
case 2:
retcode = decode(datafile, keyfile)
if (retcode != 0) printf("error, %d\0", retcode)
break
case 3:
loop = 0
break
default:
break
}
if (0 == loop) break
}
return 0
}
int generateKey(int *keys, unsigned int size)
{
char str[]="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz,./\"'<>?"
size_t str_len = sizeof(str)/sizeof(str[0])
int i
srand(time(NULL))
for (i = 0 i < size ++i)
keys[i] = str[rand() % str_len]
return 0
}
int loadKey(char const *keyfile, int *keys, unsigned int size)
{
int i = 0
FILE *pfile
int retcode = 0
pfile = fopen(keyfile, "r")
if (pfile == NULL) return -1
while ( !feof(pfile) ) {
if (i < size)
fscanf(pfile, "%d ", &keys[i++])
else
break
}
fclose(pfile)
return i
}
int saveKey(char const *keyfile, int *keys, unsigned int size)
{
FILE *pfile
int i
pfile = fopen(keyfile, "w")
if (pfile == NULL) return -1
for(i = 0 i < size ++i) {
fprintf(pfile, "%d ", keys[i])
}
fclose(pfile)
return 0
}
int encode(char const *datafile, char const *keyfile)
{
char original[MAX_KEY_LENGTH] = {'\0'}
char encrypted[MAX_KEY_LENGTH] = {'\0'}
int i, size
int keys[MAX_KEY_LENGTH]
FILE *pdatafile, *pkeyfile
pkeyfile = fopen(keyfile, "w")
if (NULL == pkeyfile) return -1
fclose(pkeyfile)
puts(" input message:")
gets(original)
size = strlen(original)
if (0 != generateKey(keys, size)) return -2
if (0 != saveKey(keyfile, keys, size) ) return -3
pdatafile = fopen(datafile, "w")
if (NULL == pdatafile) return -4
for (i = 0 i < size ++i) {
encrypted[i] = original[i] + keys[i]
fputc(encrypted[i], pdatafile)
fputc(encrypted[i], stdout)
}
printf("\n")
fclose(pdatafile)
return 0
}
int decode(char const *datafile, char const *keyfile)
{
FILE *pdatafile, *pkeyfile
int keys[MAX_KEY_LENGTH] = {0}
char original[MAX_KEY_LENGTH] = {'\0'}
char encrypted[MAX_KEY_LENGTH] = {'\0'}
int i, size
pkeyfile = fopen(keyfile, "r")
if (NULL == pkeyfile) return -1
fclose(pkeyfile)
pdatafile = fopen(datafile, "r")
if (NULL == pdatafile) return -2
fscanf(pdatafile,"%s",encrypted)
fclose(pdatafile)
size = loadKey(keyfile, keys, MAX_KEY_LENGTH)
if (size < 1) return -3
for (i = 0 i < strlen(encrypted) ++i) {
original[i] = encrypted[i]-keys[i]
fputc(original[i], stdout)
}
printf("\n")
return 0
}
运行结果：
1. Encryption.
2. Decryption.
3. Exit.
Selection (1,2,3):1
input message:
this is A test!
╓┐»╞Lñ╗ù|t▄╬╢╒è
1. Encryption.
2. Decryption.
3. Exit.
Selection (1,2,3):2
this is A test!
1. Encryption.
2. Decryption.
3. Exit.
Selection (1,2,3):3
文件分为文本文件和二进制文件。加密方法也略有不同。1、文本文件
加密的主要是文本的内容，最简单的方法就是修改文档的内容，比如1.txt中的文件内容：
abcd
只要给每一个字符+1，就可以实现加密。文件内容即会变为
bcde
2、二进制文件加密
二进制文件加密也就是对应用程序加密，需要理解可执行文件格式，比如Windows平台的Exe文件它是PE结构，Linux上的可执行文件是ELF结构，要对这样的程序进行加密，实际上是开发一种叫做“壳”的程序，这种程序的开发，需要将扎实的底层基础，同时也需要对软件加密解密有细致的理解，比如流行的vmprotect、z壳以及早些年的upx壳、aspack等等。
3、无论哪种加密都牵涉到文件操作的问题，使用C语言进行文件操作时，极少使用C标准库中的I/O函数，大多数使用操作系统提供的内存文件映射相关的API函数，有兴趣，可以搜索相关的资料。
