XOR 仅部分解密文件

Question

我正在学习 C，而且进展缓慢，因为我在自学。我正在尝试创建一个读取文件的小函数，XOR 逐字节对其进行加密，然后将其吐出。好像可以加密，但是解密的时候只有一半清晰，剩下的都是乱码。

int encrypt_file(void)
{
         //declare variables used
         FILE *src_file_ptr;
         FILE *dst_file_ptr;
         char infilename[96];
         char key[50];
         char outfilename[96];
         char temp_store[50];
         int plen;
 
         printf("Please enter the name of the file to encrypt: ");
         scanf("%s", infilename);
         printf("Please enter the name of the output file: ");
         scanf("%s", outfilename);
         printf("Please enter the key to encrypt the file: ");
         scanf("%s", key);
         plen = strlen(key);
         
         //test for existence of input file
         src_file_ptr = fopen(infilename, "r");
         if (src_file_ptr == NULL)
         {
                 printf("File does not exist!");
                 return 1;
         }       
         
         dst_file_ptr = fopen(outfilename, "a");
         //read and process file 50 bytes at a time
         while(fgets(temp_store, 50, src_file_ptr) != NULL)
         {
                 int i;
                 //XOR n bytes with key
                 for ( i = 0; i < strlen(temp_store); i++)
                 {
                         temp_store[i] = temp_store[i] ^ key[i%plen];
                         fprintf(dst_file_ptr,"%c",temp_store[i]);
                 }
 
         }
         fclose(dst_file_ptr);
         fclose(src_file_ptr);
         return 0;
 
}

int main(void)
{
   encrypt_file();
   return 0;
}

我在这里对堆栈溢出进行了广泛的研究，我发现的所有内容都是用于 XOR 加密/解密设置值字符串的。我试图通过读取文件并向用户询问密码（密钥）来使其动态工作。任何帮助将不胜感激。

Answer 1

所以在头撞到墙上更加痛苦之后，在这里的人的帮助下，我找到了解决方案。

int encrypt_file(void)
   {
         //declare variables used
         FILE *src_file_ptr;
         FILE *dst_file_ptr;
         char infilename[96];
         char key[50];
         char outfilename[96];
         char temp_store[50];
         int plen;
 
         printf("Please enter the name of the input file: ");
         scanf("%s", infilename);
         printf("Please enter the name of the output file: ");
         scanf("%s", outfilename);
         printf("Please enter the key to perform encrypt / decrypt: ");
         scanf("%s", key);
         plen = strlen(key);
 
         //test for existence of input file
         src_file_ptr = fopen(infilename, "rb");
         if (src_file_ptr == NULL)
         {
                 printf("File does not exist!");
                 return 1;
         }
 
         dst_file_ptr = fopen(outfilename, "wb");
         //create and initialize iterator
         int i = 0;
         do
         {
                 //variable for new byte
                 char nb;
                 // check for end of file and exit if found
                 if (feof(src_file_ptr))
                         break;
                 //check where iterator is at. If same length as password, reset it.
                 if (i == plen)
                 {
                         i = 0;}
                 //read single character from file, in binary mode
                 char c = fgetc(src_file_ptr);
                 // combine file character with password character using XOR
                 nb = c ^ key[i];
                 //write new character to file as byte
                 fputc(nb, dst_file_ptr);
                 //increment to next letter in password
                 i++;
 
         } while(1);
         fclose(dst_file_ptr);
         fclose(src_file_ptr);
         return 0;
 }

int main(void)
{
encrypt_file();
return 0;
}

这对文本文件非常有效，还没有尝试过二进制文件，但到目前为止我只需要纯文本。

XOR 仅部分解密文件

XOR only partially decrypts file

c

xor