encryption driver SfReadcompletion() routine

NTFSD
1

Hi all

I have designed an
encryption filter driver, first I used a simple encryption algorithm, it works
well. I replace simple encrypt algorithm with the standard encryption algorithm
(DES) but decryption doesn’t work correct and I don’t retrieve the correct plain
data (I test des algorithm outside of my code and it works correct!?).

I Look thru the archives and FAQ.I found that
In??? read completion, we can decrypt
buffer in place (don’t need to create another buffer for this)so

?

My code as following:

NTSTATUS

SfReadCompletion(

IN PDEVICE_OBJECT
DeviceObject,

IN PIRP Irp,

IN PVOID Context

(

This function is the
read completion routine for this // file system driver?
?filter//

{

…

if(Found) //file is in
the protected place

{

if(Irp->Flags &(IRP_PAGING_IO
| IRP_NOCACHE | IRP_SYNCHRONOUS_PAGING_IO))

{

if(Irp->MdlAddress)

UserBuffer = MmGetSystemAddressForMdlSafe(

Irp->MdlAddress,HighPagePriority);

else

UserBuffer = Irp->UserBuffer;

//use des algorithm

decrypt(UserBuffer ,key ,UserBuffer
,size);

?

}

}

…

}

is this my code wrong? Or
my problem is because of bad implementation of des algorithm?

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2

Do you account for the fact that you may get I/O that is not aligned on an even block boundary for your chosen cipher?

If your “simple encryption algorithm” was to, say, simply xor every byte in the I/O with a constant, then that does not really represent the complexities inherent in an encryption filter particularly well.

  • S

From: fatima Gh
Sent: Saturday, October 18, 2008 11:08
To: Windows File Systems Devs Interest List
Subject: [ntfsd] encryption driver SfReadcompletion() routine

Hi all
I have designed an encryption filter driver, first I used a simple encryption algorithm, it works well. I replace simple encrypt algorithm with the standard encryption algorithm (DES) but decryption doesn’t work correct and I don’t retrieve the correct plain data (I test des algorithm outside of my code and it works correct!?).
I Look thru the archives and FAQ.I found that In read completion, we can decrypt buffer in place (don’t need to create another buffer for this)so

My code as following:
NTSTATUS
SfReadCompletion(
IN PDEVICE_OBJECT DeviceObject,
IN PIRP Irp,
IN PVOID Context
(
This function is the read completion routine for this // file system driver filter//
{
…
if(Found) //file is in the protected place
{
if(Irp->Flags &(IRP_PAGING_IO | IRP_NOCACHE | IRP_SYNCHRONOUS_PAGING_IO))
{
if(Irp->MdlAddress)
UserBuffer = MmGetSystemAddressForMdlSafe(
Irp->MdlAddress,HighPagePriority);
else
UserBuffer = Irp->UserBuffer;
//use des algorithm
decrypt(UserBuffer ,key ,UserBuffer ,size);

}
}
…
}
is this my code wrong? Or my problem is because of bad implementation of des algorithm?

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