RE: encrypted or decrypted several times?

NTFSD
1

Hi Slava Imameyev,

Do not try to encrypt/decrypt data steram in a filter, it is impossible to do correctly if an underlying
FSD communicates with the Cache Manager.
Can you give me a concrete explaination? You mean FSD get the file data by reading disk directly, and copywrite to cache? Does ntfs or fat32 have such operation?

2

> Can you give me a concrete explaination? You mean FSD get the file data by

reading disk directly, and copywrite to cache? Does ntfs or fat32 have such

On compressed or encrypted files, NTFS allocates the temporary memory, uses it
to send the disk IO IRPs down, and then decompresses/decrypts the data from the
temporary memory to the main (noncached) IO IRP’s buffer.

So, the cache always contains cleartext, and you can use memory-mapped
compressed and encrypted files.

Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
xxxxx@storagecraft.com
http://www.storagecraft.com

3

>Can you give me a concrete explaination?

I meant that it is impossible to foresee whether the cache will be used for
user’s non-cached requests or data will be read directly from the disk for
user’s cached requests.

–
Slava Imameyev, xxxxx@hotmail.com

wrote in message news:xxxxx@ntfsd…
> Hi Slava Imameyev,
>
>>Do not try to encrypt/decrypt data steram in a filter, it is impossible to
>>do correctly if an underlying
> FSD communicates with the Cache Manager.
> Can you give me a concrete explaination? You mean FSD get the file data by
> reading disk directly, and copywrite to cache? Does ntfs or fat32 have
> such operation?
>