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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
void decodeEmail(char encoded[])
{
int len = strlen(encoded);
char temp[3];
char email[len/2];//the encoded string/2 gives the length of the result email+1
memcpy(temp, encoded, 2);
temp[2] = '\0';
char xorKey = strtol(temp, NULL, 16);//the value of the xorKey is the first two bytes in hex, encoded in UTF-8
int j = 0;
for (int i = 2; i < len; i += 2, ++j)//decode the rest of the two bytes
{
memcpy(temp, encoded+i,2);
temp[2] = '\0';
email[j] = strtol(temp, NULL, 16) ^ xorKey;//xor two bytes with the xorkey to get a UTF-8 character
}
email[j] = '\0';//terminate the string
printf("Decoded email: %s\n", email);
}
int main(int argc, char *argv[])
{
if (!argv[1])
{
char input[512+1];//as the maximun length of an email should be 255 chars, we allocate 255*2+2 chars for the longest valid input (+1 for the newline)
fprintf(stderr,"Input email to decode (string within data-cfemail=\"\"): ");
ssize_t length = read(0, input, 512);
if (length < 5){fprintf(stderr,"Invalid input.\n"); exit(1);}
input[length-1] = '\0';//overwrite newline with null char
decodeEmail(input);
}
else
{
if (strlen(argv[1]) < 4 || strlen(argv[1]) > 512){fprintf(stderr,"Invalid input.\n"); exit(1);}
decodeEmail(argv[1]);
}
//test string: e4908d9497a4908b9696818a90829681858fca878b89
}
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