Dear All,
I am sorry to bother you...I need your help...
Have you faced such problem - loose some data at the end of a buffer...
The code is like this
I want to encrypt a file 1024 blocks by 1024 blocks
and at the final block which is not 1024 blocks will do the final management
like follows:
============================================================================
unsigned char inbuf[1024], outbuf[1024];
// Obtain the file size
fseek(fin, 0, SEEK_END);
size = ftell(fin);
rewind(fin);
buffer = (char *)malloc(size);
output = (char *)malloc(size);
int shift = 0;
int kBufferSize = 1024;
fread(buffer, 1, size, fin);
if (buffer == NULL) exit(2);
// THE PROBLEM STARTS HERE, TAKE 1024 BYTES SLIDINGLY
while (shift < size) {
inlen = 0;
for (int i=0; i<kBufferSize; i++) {
if (i+shift < size){
inbuf[i] = (unsigned)buffer[i+shift];
inlen++;
}
}
if (!EVP_DecryptUpdate(&ctx, outbuf, &outlen, inbuf, inlen)) {
printf("ERROR 1");
exit(-1);
}
for (int j=0; j<outlen; j++)
if (j+shift < size) {
output[j+shift] = (char)outbuf[j];
printf("%c", output[j+shift]); //PRINT 1
}
shift+=kBufferSize;
}
if (!EVP_DecryptFinal(&ctx, outbuf, &outlen)) {
printf("ERROR 2");
exit(-1);
}
for (int k=0; k<outlen; k++) {
output[k+shift] = (char)outbuf[k];
printf("%c", output[k+shift]); //PRINT 2
}
printf("\nsize:%d\n", size); // PRINT 3
printf("output size:%d\n", strlen(output)); // PRINT 4
for (int x=0; x<size; x++) {
printf("%c", output[x]); // PRINT 5
}
fwrite(output, 1, size, fout);
============================================================================
===
You don't have to look into the codes. When I try to deal with a file
"test.txt" which has a sentence "This is a test.". The problem is at the end
of the code, it prints out:
This is a test. //THIS IS THE CORRECT DATA IN OUTPUT BUFFER (PRINT 1 & 2)
size: 16 //THIS IS THE SIZE OF THE FILE WHICHI IS CORRECT TOO (PRINT 3)
output size: 8 //NOW I DON'T UNDERSTAND WHY HERE... (PRINT 4)
This is //THERE IS SOME DATA MISSED IN THE OUTPUT BUFFER (PRINT 5)
Please help me if you have the time. I don't know why there is some data
lost in the buffer...
Thousand thanks. Wish you all the best.
Best regards,
--------------------------------------------
Jordan Cheun Ngen, Chong
INF-4067 Universiteit Twente
Postbus 217
7500 AE Enschede
The Netherlands
Distributed and Embedded Systems (DIES)
--------------------------------------------
Office Phone: +31 53 4894655
Web site: http://www.cs.utwente.nl/~chong
Email Add.: [EMAIL PROTECTED]
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