I am in the process of writing a decipher algorithm for Vegenere Variant Cipher and ran into some C specific issues(I am not too familiar with C).
I get
"Run-Time Check Failure #2 - Stack around the variable 'ch' was corrupted
" error.
If I understand the error right, ch
is not available when I try to read/write to it(ch
in this case represents a HEX value read from the text file, I have posted the code of the function below).
But, for the life of me, I can't figure out where it happens. I close the file way before the I exit the function(exception is thrown at the time I leave the function).
Can you take a look an let me know where I have it wrong? Thanks in advance.
P.S. I am tagging the question with C++ as well as it should pretty much be the same except, maybe, how we read the file in. Anyways, my code below:
int getKeyLength(char *cipherTxtF){
int potKeyL = 1;
float maxFreq = 0.00;
int winKL = 1;
for (potKeyL = 1; potKeyL <= 13; potKeyL++)// loop that is going through each key size startig at 1 and ending at 13
{
unsigned char ch;
FILE *cipherTxtFi;
cipherTxtFi = fopen(cipherTxtF, "r");
int fileCharCount = 0;
int freqCounter[256] = { 0 };
int nThCharCount = 0;
while (fscanf(cipherTxtFi, "%02X", &ch) != EOF) {
if (ch != '\n') {
if (fileCharCount % potKeyL == 0){
int asciiInd = (int)ch;
freqCounter[asciiInd] += 1;
nThCharCount++;
}
}
fileCharCount++;
}
fclose(cipherTxtFi);
float frequenciesArray[256] = { 0 };
float sumq_iSq = 0;
int k;
for (k = 0; k < 256; k++){
frequenciesArray[k] = freqCounter[k] / (float)nThCharCount;
}
for (k = 0; k < 256; k++){
sumq_iSq += frequenciesArray[k] * frequenciesArray[k];
printf("%f \n", sumq_iSq);
}
if (maxFreq < sumq_iSq) {
maxFreq = sumq_iSq;
winKL = potKeyL;
}
}
return winKL;
}
You are trying to read an hexadecimal integer with fscanf()
(format "%02X", where X means "integer in hex format") and store it into a char
.
Unfortuantely fscanf()
just receives the address of the char and doesn't know that you've not provided the address of an int
. As int
is larger than a char
, the memory gets corrupted.
A solution could be:
int myhex;
while (fscanf(cipherTxtFi, "%02X", &myhex) != EOF) {
ch = myhex;
...