How to read pkcs#7 file properly - c++

Question

I have a file with detached pkcs#7 signature of size 267 bytes. I create it after executing
CryptSignMessage(
&SigParams,
TRUE,
1,
MessageArray,
MessageSizeArray,
pbSignedMessageBlob,
&cbSignedMessageBlob)
function and then I write content of pbSignedMessageBlob:
pbSignedMessageBlob[cbSignedMessageBlob] = '\0';
FILE *file;
file = fopen("c:\\path\\sign_pkcs7.pk7", "wb");
fwrite(pbSignedMessageBlob, sizeof(BYTE), cbSignedMessageBlob, file);
fclose(file);
Then I try to verify this signature and read this file:
BYTE *pkcsContent;
FILE *file3;
file3 = fopen("c:\\users\\timur\\desktop\\sign_pkcs7.pk7", "rb");
pkcsContent = MyReadFile(file3, cbArray);
BYTE* MyReadFile(FILE *f, DWORD &len)
{
size_t result;
BYTE *buffer;
if (f == NULL)
{
fputs ("File error", stderr);
exit (1);
}
fseek (f, 0, SEEK_END);
len = ftell (f);
rewind (f);
//buffer = (BYTE*) malloc (sizeof(char)*lSize);
buffer = new BYTE[len + 1];
if (buffer == NULL)
{
fputs ("Memory error", stderr);
exit (2);
}
result = fread (buffer, 1, len, f);
if (result != len)
{
fputs ("Reading error",stderr);
exit (3);
}
buffer[len] = '\0';
fclose (f);
return buffer;
}
But the file content I get into pkcsContent is only 37 bytes length.
I also tried to manage files using std::fstream, but result is the same. Maybe the way I'm writing file to disk is wrong?

Answer 1

Are you trying to compute the length of pkcsContent with strlen (this is my guess since you're null-terminating the buffer in MyReadFil)? You can't do that because PKCS#7 is binary data and it can contain 0 anywhere.