Thread: Problems with Xor encryption

vart

Amazing! It worked! Thank you =)

Here's the code in case someone wants it:

Code:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
    FILE *fp;
    long fSize;
    size_t result;
    char key[] = "123", *buffer;

    fp = fopen ("xor.txt", "rb+");
    
    if (fp == NULL)
       {fputs("File error",stderr); exit(1);}
       
    fseek (fp, 0, SEEK_END);
    fSize = ftell (fp);
    rewind (fp);
    
    buffer = malloc (sizeof(char)*fSize);
    
    if (buffer == NULL)
       {fputs ("Memory error",stderr); exit (2);}
       
    result = fread (buffer, 1, fSize, fp);
    
    if (result != fSize)
       {fputs ("Reading error",stderr); exit (3);}
       
    XorEncrypt(buffer, key);
    
    rewind (fp);
    fwrite (buffer, 1, fSize, fp);
    
    fclose(fp);
    free(buffer);
    getch();
    return 0;
}

int XorEncrypt (char *string, char *key)
{
    int i, j, mod;
    
    int StringLen = strlen(string); // 20
    int KeyLen = strlen(key); // 6

    for (i = 0; i < (StringLen / KeyLen); i++)
    {
        for (j = 0; j < KeyLen; j++)
        {
            string[i*KeyLen + j] ^= key[j];
        }
    }
    
    mod = StringLen &#37; KeyLen;
    
    if (mod != 0)
    {
         for (i = 0; i < mod; i++)
         {
             string[StringLen - mod + i] ^= key[i];
         }
    }
    
    return 0;
}

Well actually not really.....

When I use small strings in the file it works finely, but with larger texts and files...

Example: (using key "test43")

"This is a test!!!" -> " ZET@VRU" -> "This is a test!!!"

But when I placed the code (the same I just posted) and then passed the output I got:

Code:

#includ SHGGZ\
yoPZP]QZ
My>>~ ^\]] ESPXEUATOSE/8Zy>HyoST2,?1Hy>TES[]E']I^~~TE NV+SQ@
	O99TESTW[SQJ/8SIEW@V^RV^~~99TESTRCTXS[CS\K] LGVISVFQ_GZO99TEST99TEST]UTMIE=!x]hyTTESTOU2VFA]^SLZ MB]NyoSTTESy>TESGVS\RCXECX`1 8+q}0LHy>TESgZ SIU  ZO99TESTFVZO99TEST99TESTVFTX\E[]I
\W[Z^R`]>~EST>~ESTZE[AU 
T	T+&8xyoSTTESRC
 T9 FJT 
[AVI  PVZOVT
]^y>TESTyoST  
XGTXSFV
S\VFEISgZ _TRC]^~~TE~~TE  
XGTDNTR`]99TESTTAGE[VfV
S
FXQALHTQKS\O~~TEST>~ESTk6WA
\VF 
]>~EST>~ESTAP\]>~ESTU Q\RVISE6QT]>~EST>~ESTU	QZO99TESTRA [AU 
]>~ESTTOhyTT AAECO99	hyy>ZS,[A1MC E[\REY@AXP
TXZy>HyoSTT]T_TY\^~~TE~~TE@'
ZT8 T	
Q]\]]LHTTWCy>TESZGT.
xVENTGG	XZO[EEy>>~ESTUS\]IECOZTYS\gGxVE\TV
)TX_>~ESTHyoSTTESTR\E[TUHT^HE8MHT^_L~~TESThyTTESTTES@A/]? 
8Q]TNSi*XSQJ/.O99TESTTEy>TES	99TEST99TESTY\ENTgGxVEVTV
)>~EST>~ESTZE[[WTDNTyoSThyTTEST

TZTXSDEOTY\^S]hyTTESThyTTESTTESTGGo` SSY^
S_Z)E-IX(iyoSTTESTNyoST	hyTThyTT AAECO99

=S There must be something wrong with the algo right?

Originally Posted by Salem

Code:

#include
test43test43

What value do you get when you exclusive-or a letter with itself?
What do you think strlen() is going to do when it gets to that value?

If lala123 had been paying attention, he/she would have seen that I already pointed this out

Oh, thanks for that. The code is working now.

Code:

int XorEncrypt (char *string, char *key, long sLen)
{
    int i, j, mod;
    
    int KeyLen = strlen(key); // 6

    for (i = 0; i < (sLen / KeyLen); i++)
    {
        for (j = 0; j < KeyLen; j++)
        {
            string[i*KeyLen + j] ^= key[j];
        }
    }
    
    mod = sLen &#37; KeyLen;
    
    if (mod != 0)
    {
         for (i = 0; i < mod; i++)
         {
             string[sLen - mod + i] ^= key[i];
         }
    }
    
    return 0;
}

Oh and BTW Im a man...

Originally Posted by lala123

Oh and BTW Im a man...

Not like it matters, I just don't want to mistakenly refer to a woman as "he" or a man as "she" so I just use both

Ok