when and where shall I encrypt dentry?

when and where shall I encrypt dentry?

[Vineet Joglekar]

Hi all,



I am trying to add some cryptographic functionality to ext2 file system for my masters project. I am working with kernel 2.4.21



Along with regular files, I intend to encrypt directory contents too. For reading I guess the function ext2_get_page in fs/ext2/dir.c is used. Hence I can put my decryption routine in that function. Is that correct?



I was trying to look for the routine which writes the dentry on disk, but was unable to find it. I found out that the function d_instantiate is used to fill in inode information for a dentry, but unable to see when it is written on disk. I suppose that I have to encrypt the dentry just before writing on to the disk, as if i encrypt it before, other functions using it wont be able to access until they decrypt. So please help me with this, that when and where shall I encrypt the directory contents.



Thanks and regards,



Vineet

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Re: when and where shall I encrypt dentry?

[linux-os]

The correct place to encrypt or decrypt ANYTHING is
just before access to the "outside" world, i.e., in the
case of a file-system, the reads and writes to the
storage device (disk drive). You are in a world of
hurt if you intend to encrypt 'data' and directories
separately.

If you need to use an existing file-system and then
encrypt it, you use the same technique but your
"storage device" is a "container file" that you mount
using the loop device. This allows you to have an
encrypted file-system below some mount-point and
a normal file-system above.

FYI, there are existing tools/code that allow one to
mount an encrypted file-system. Perhaps your masters
project just got easier?


On Wed, 2 Feb 2005, Vineet Joglekar wrote:

>
> Hi all,
>
> I am trying to add some cryptographic functionality to ext2 file system for my masters project. I am working with kernel 2.4.21
>
> Along with regular files, I intend to encrypt directory contents too. For reading I guess the function ext2_get_page in fs/ext2/dir.c is used. Hence I can put my decryption routine in that function. Is that correct?
>
> I was trying to look for the routine which writes the dentry on disk, but was unable to find it. I found out that the function d_instantiate is used to fill in inode information for a dentry, but unable to see when it is written on disk. I suppose that I have to encrypt the dentry just before writing on to the disk, as if i encrypt it before, other functions using it wont be able to access until they decrypt. So please help me with this, that when and where shall I encrypt the directory contents.
>
> Thanks and regards,
>
> Vineet
>
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Dick Johnson
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