HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
Cary
Cant you use cyphertext stealing ?
Dan
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Monday, July 15, 2002 7:59 PM
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
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It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and
decryption on Windows XP NTFS file system. Due to using block cipher (16
bytes long). I need change file size to be 16 bytes boundary. It works
perfect on FAT, but on NTFS, file size after change always being resized
by file system to be 8 bytes boundary. Is there someone happend to know
what is wrong here? How can I change file size to 16 bytes boundary on
NTFS. Thanks for any input.
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Thank you. I don’t think so. I have to use same cipher as other products did.
Cary
----- Original Message -----
From: Dan Partelly
To: File Systems Developers
Sent: Monday, July 15, 2002 10:18 AM
Subject: [ntfsd] Re: Change file size on NTFS
Cant you use cyphertext stealing ?
Dan
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Monday, July 15, 2002 7:59 PM
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
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Thank you. But is wouldn’t work.
Cary
----- Original Message -----
From: Jamey Kirby
To: File Systems Developers
Sent: Monday, July 15, 2002 10:41 AM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
Cary
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I would suggest that no encryption of a general purpose modify the size of a file. That can and will create more problems than it solves. Step 1: a simple solution is to take the last remaining 1-15 bytes and add enough bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it again and do it last on encrypt and first on decrypt - that could be reversed if desired. You need someone, not me, who understands encryption - RSA comes to mind - and can help you maintain strong encryption over the entire file. I also hope you consider CBC so a 10MB file of all zeroes doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby
To: File Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
Cary
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Thank you. The step 1 as you mentioned is just what I did. The problem is, when pagging IO, I don’t have the file size, so, I have to change file size when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same experience?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a file. That can and will create more problems than it solves. Step 1: a simple solution is to take the last remaining 1-15 bytes and add enough bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it again and do it last on encrypt and first on decrypt - that could be reversed if desired. You need someone, not me, who understands encryption - RSA comes to mind - and can help you maintain strong encryption over the entire file. I also hope you consider CBC so a 10MB file of all zeroes doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby
To: File Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
Cary
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Let me try a diagram:
[Data nnnnnnnn bytes mod 16] [15 bytes of data]
Do NOT change file size as it just won’t work easily and is not needed for a general purpose directory based encryption program.
I think you have the filesize available in the FileObject. It is available from the FSD is you ask.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you. The step 1 as you mentioned is just what I did. The problem is, when pagging IO, I don’t have the file size, so, I have to change file size when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same experience?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a file. That can and will create more problems than it solves. Step 1: a simple solution is to take the last remaining 1-15 bytes and add enough bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it again and do it last on encrypt and first on decrypt - that could be reversed if desired. You need someone, not me, who understands encryption - RSA comes to mind - and can help you maintain strong encryption over the entire file. I also hope you consider CBC so a 10MB file of all zeroes doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby
To: File Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
Cary
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Thank you very much. But how does it work when nnnnnnnn < 16?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Tuesday, July 16, 2002 1:26 PM
Subject: [ntfsd] RE: Change file size on NTFS
Let me try a diagram:
[Data nnnnnnnn bytes mod 16] [15 bytes of data]
Do NOT change file size as it just won’t work easily and is not needed for a general purpose directory based encryption program.
I think you have the filesize available in the FileObject. It is available from the FSD is you ask.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you. The step 1 as you mentioned is just what I did. The problem is, when pagging IO, I don’t have the file size, so, I have to change file size when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same experience?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a file. That can and will create more problems than it solves. Step 1: a simple solution is to take the last remaining 1-15 bytes and add enough bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it again and do it last on encrypt and first on decrypt - that could be reversed if desired. You need someone, not me, who understands encryption - RSA comes to mind - and can help you maintain strong encryption over the entire file. I also hope you consider CBC so a 10MB file of all zeroes doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby
To: File Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
Cary
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A different encryption algorithm is required. You can’t encrypt files of < 16 bytes with any real security with any algorithm suited for block encryption. Each 16 byte block contributes to the next block and increases encryption strength. That is why most encryption algorithms are based upon 512, 2048, or 4096 blocks. There are stream ciphers, but they are a solution for a different problem.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 6:19 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much. But how does it work when nnnnnnnn < 16?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Tuesday, July 16, 2002 1:26 PM
Subject: [ntfsd] RE: Change file size on NTFS
Let me try a diagram:
[Data nnnnnnnn bytes mod 16] [15 bytes of data]
Do NOT change file size as it just won’t work easily and is not needed for a general purpose directory based encryption program.
I think you have the filesize available in the FileObject. It is available from the FSD is you ask.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you. The step 1 as you mentioned is just what I did. The problem is, when pagging IO, I don’t have the file size, so, I have to change file size when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same experience?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a file. That can and will create more problems than it solves. Step 1: a simple solution is to take the last remaining 1-15 bytes and add enough bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it again and do it last on encrypt and first on decrypt - that could be reversed if desired. You need someone, not me, who understands encryption - RSA comes to mind - and can help you maintain strong encryption over the entire file. I also hope you consider CBC so a 10MB file of all zeroes doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby
To: File Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
Cary
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Hi All,
I often see this question come up and often see poor responses from people
:). Most block ciphers can be used in many different modes, not just the
ones that are randomly pulled out of a hat (normally ECB + CBC). Have you
ever looked at “Counter Mode” this is a modified OFB method that uses an
initialisation vector (IV) + key to generate the next block for encryption.
You can use this mode to encrypt any size buffer/file and simply discard
what you don`t use. Counter Mode also has the ability of random access to
data as block x is not dependent on the successful decryption of block x-1.
There is heaps of information available on this kind of thing. May I suggest
investing in a copy of “Applied Cryptography”. All block cipher modes are
discussed in detail giving pros and cons of each.
Regards
Ben Curley
Data Encryption Systems Ltd.
Website: www.des.co.uk http: / www.deslock.com
http:
-----Original Message-----
From: David J. Craig [mailto:xxxxx@yoshimuni.com]
Sent: 17 July 2002 00:41
To: File Systems Developers
Subject: [ntfsd] RE: Change file size on NTFS
A different encryption algorithm is required. You can’t encrypt files of <
16 bytes with any real security with any algorithm suited for block
encryption. Each 16 byte block contributes to the next block and increases
encryption strength. That is why most encryption algorithms are based upon
512, 2048, or 4096 blocks. There are stream ciphers, but they are a
solution for a different problem.
----- Original Message -----
From: Cary Fu mailto:xxxxx
To: File Systems Developers mailto:xxxxx
Sent: Tuesday, July 16, 2002 6:19 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much. But how does it work when nnnnnnnn < 16?
Cary
----- Original Message -----
From: David mailto:xxxxx J. Craig
To: File Systems Developers mailto:xxxxx
Sent: Tuesday, July 16, 2002 1:26 PM
Subject: [ntfsd] RE: Change file size on NTFS
Let me try a diagram:
[Data nnnnnnnn bytes mod 16] [15 bytes of data]
1. Encrypt the Data nnnnnnnn bytes mod 16 first.
2. Take one byte from the end of the data encrypted in 1. and add to the
front of the 15 byte remainder.
3. Encrypt that 16 byte packet.
4. Write it to the file overlaying the one byte you took out.
5. Do the decryption in reverse order doing the last 16 bytes first and
then the mod 16 pieces of the file.
Do NOT change file size as it just won’t work easily and is not needed for a
general purpose directory based encryption program.
I think you have the filesize available in the FileObject. It is available
from the FSD is you ask.
----- Original Message -----
From: Cary Fu mailto:xxxxx
To: File Systems Developers mailto:xxxxx
Sent: Tuesday, July 16, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you. The step 1 as you mentioned is just what I did. The problem is,
when pagging IO, I don’t have the file size, so, I have to change file size
when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same
experience?
Cary
----- Original Message -----
From: David J. Craig mailto:xxxxx
To: File Systems Developers mailto:xxxxx
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a
file. That can and will create more problems than it solves. Step 1: a
simple solution is to take the last remaining 1-15 bytes and add enough
bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it
again and do it last on encrypt and first on decrypt - that could be
reversed if desired. You need someone, not me, who understands encryption -
RSA comes to mind - and can help you maintain strong encryption over the
entire file. I also hope you consider CBC so a 10MB file of all zeroes
doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby mailto:xxxxx
To: File mailto:xxxxx Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com
mailto:xxxxx
[mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and
decryption on Windows XP NTFS file system. Due to using block cipher (16
bytes long). I need change file size to be 16 bytes boundary. It works
perfect on FAT, but on NTFS, file size after change always being resized by
file system to be 8 bytes boundary. Is there someone happend to know what is
wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks
for any input.
Cary
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Thank you very much.
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Tuesday, July 16, 2002 4:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
A different encryption algorithm is required. You can’t encrypt files of < 16 bytes with any real security with any algorithm suited for block encryption. Each 16 byte block contributes to the next block and increases encryption strength. That is why most encryption algorithms are based upon 512, 2048, or 4096 blocks. There are stream ciphers, but they are a solution for a different problem.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 6:19 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much. But how does it work when nnnnnnnn < 16?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Tuesday, July 16, 2002 1:26 PM
Subject: [ntfsd] RE: Change file size on NTFS
Let me try a diagram:
[Data nnnnnnnn bytes mod 16] [15 bytes of data]
Do NOT change file size as it just won’t work easily and is not needed for a general purpose directory based encryption program.
I think you have the filesize available in the FileObject. It is available from the FSD is you ask.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you. The step 1 as you mentioned is just what I did. The problem is, when pagging IO, I don’t have the file size, so, I have to change file size when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same experience?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a file. That can and will create more problems than it solves. Step 1: a simple solution is to take the last remaining 1-15 bytes and add enough bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it again and do it last on encrypt and first on decrypt - that could be reversed if desired. You need someone, not me, who understands encryption - RSA comes to mind - and can help you maintain strong encryption over the entire file. I also hope you consider CBC so a 10MB file of all zeroes doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby
To: File Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
Cary
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The paging IO requests that are written to the disk are usually in 512 blocks or some multiple of 512. Of course, the file system may not pass all of the 512 bytes every time, but you might be able to do some investigation and use that fact. The only problems deal with something copying the file if the bytes beyond the EOF are needed for decryption. A program that bypasses the cache with the no cache flag might be a problem. Someone else suggested learning about encryption algorithms and determine one that will work in your environment. I know some who like blowfish 448, triple DES, RC5, and AES. You need to have a consultant from RSA or Counterpane help you with the algorithms.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Wednesday, July 17, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much.
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Tuesday, July 16, 2002 4:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
A different encryption algorithm is required. You can’t encrypt files of < 16 bytes with any real security with any algorithm suited for block encryption. Each 16 byte block contributes to the next block and increases encryption strength. That is why most encryption algorithms are based upon 512, 2048, or 4096 blocks. There are stream ciphers, but they are a solution for a different problem.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 6:19 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much. But how does it work when nnnnnnnn < 16?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Tuesday, July 16, 2002 1:26 PM
Subject: [ntfsd] RE: Change file size on NTFS
Let me try a diagram:
[Data nnnnnnnn bytes mod 16] [15 bytes of data]
Do NOT change file size as it just won’t work easily and is not needed for a general purpose directory based encryption program.
I think you have the filesize available in the FileObject. It is available from the FSD is you ask.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you. The step 1 as you mentioned is just what I did. The problem is, when pagging IO, I don’t have the file size, so, I have to change file size when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same experience?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a file. That can and will create more problems than it solves. Step 1: a simple solution is to take the last remaining 1-15 bytes and add enough bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it again and do it last on encrypt and first on decrypt - that could be reversed if desired. You need someone, not me, who understands encryption - RSA comes to mind - and can help you maintain strong encryption over the entire file. I also hope you consider CBC so a 10MB file of all zeroes doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby
To: File Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
Cary
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>> The paging IO requests that are written to the disk are usually in 512 blocks
minimum page size in IA32 architecture is 0x1024.
> You need to have a consultant from RSA or Counterpane help you with the algorithms.
What for ? Pay big US$ for a thing which is throughly discussed all over the NET ? All it takes is reading and a bit of research.
Dan
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Wednesday, July 17, 2002 10:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
The paging IO requests that are written to the disk are usually in 512 blocks or some multiple of 512. Of course, the file system may not pass all of the 512 bytes every time, but you might be able to do some investigation and use that fact. The only problems deal with something copying the file if the bytes beyond the EOF are needed for decryption. A program that bypasses the cache with the no cache flag might be a problem. Someone else suggested learning about encryption algorithms and determine one that will work in your environment. I know some who like blowfish 448, triple DES, RC5, and AES. You need to have a consultant from RSA or Counterpane help you with the algorithms.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Wednesday, July 17, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much.
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Tuesday, July 16, 2002 4:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
A different encryption algorithm is required. You can’t encrypt files of < 16 bytes with any real security with any algorithm suited for block encryption. Each 16 byte block contributes to the next block and increases encryption strength. That is why most encryption algorithms are based upon 512, 2048, or 4096 blocks. There are stream ciphers, but they are a solution for a different problem.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 6:19 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much. But how does it work when nnnnnnnn < 16?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Tuesday, July 16, 2002 1:26 PM
Subject: [ntfsd] RE: Change file size on NTFS
Let me try a diagram:
[Data nnnnnnnn bytes mod 16] [15 bytes of data]
Do NOT change file size as it just won’t work easily and is not needed for a general purpose directory based encryption program.
I think you have the filesize available in the FileObject. It is available from the FSD is you ask.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you. The step 1 as you mentioned is just what I did. The problem is, when pagging IO, I don’t have the file size, so, I have to change file size when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same experience?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a file. That can and will create more problems than it solves. Step 1: a simple solution is to take the last remaining 1-15 bytes and add enough bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it again and do it last on encrypt and first on decrypt - that could be reversed if desired. You need someone, not me, who understands encryption - RSA comes to mind - and can help you maintain strong encryption over the entire file. I also hope you consider CBC so a 10MB file of all zeroes doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby
To: File Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
Cary
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You get what you pay for and are willing to accept. Netscape discovered that even though they had good algorithms, a minor deficiency in their random number generator routine made brute force attacks very easy. I want someone with experience to look at my implementation and see if some mistake has made the encryption less secure than it should be. If you are using a toolkit from RSA, you should be able to write something that works well, but I still want someone else to look unless the toolkit implements all elements of the algorithm in a fool proof way - if that is even possible!
----- Original Message -----
From: Dan Partelly
To: File Systems Developers
Sent: Wednesday, July 17, 2002 5:21 PM
Subject: [ntfsd] RE: Change file size on NTFS
> The paging IO requests that are written to the disk are usually in 512 blocks
minimum page size in IA32 architecture is 0x1024.
> You need to have a consultant from RSA or Counterpane help you with the algorithms.
What for ? Pay big US$ for a thing which is throughly discussed all over the NET ? All it takes is reading and a bit of research.
Dan
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Wednesday, July 17, 2002 10:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
The paging IO requests that are written to the disk are usually in 512 blocks or some multiple of 512. Of course, the file system may not pass all of the 512 bytes every time, but you might be able to do some investigation and use that fact. The only problems deal with something copying the file if the bytes beyond the EOF are needed for decryption. A program that bypasses the cache with the no cache flag might be a problem. Someone else suggested learning about encryption algorithms and determine one that will work in your environment. I know some who like blowfish 448, triple DES, RC5, and AES. You need to have a consultant from RSA or Counterpane help you with the algorithms.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Wednesday, July 17, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much.
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Tuesday, July 16, 2002 4:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
A different encryption algorithm is required. You can’t encrypt files of < 16 bytes with any real security with any algorithm suited for block encryption. Each 16 byte block contributes to the next block and increases encryption strength. That is why most encryption algorithms are based upon 512, 2048, or 4096 blocks. There are stream ciphers, but they are a solution for a different problem.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 6:19 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much. But how does it work when nnnnnnnn < 16?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Tuesday, July 16, 2002 1:26 PM
Subject: [ntfsd] RE: Change file size on NTFS
Let me try a diagram:
[Data nnnnnnnn bytes mod 16] [15 bytes of data]
Do NOT change file size as it just won’t work easily and is not needed for a general purpose directory based encryption program.
I think you have the filesize available in the FileObject. It is available from the FSD is you ask.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you. The step 1 as you mentioned is just what I did. The problem is, when pagging IO, I don’t have the file size, so, I have to change file size when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same experience?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a file. That can and will create more problems than it solves. Step 1: a simple solution is to take the last remaining 1-15 bytes and add enough bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it again and do it last on encrypt and first on decrypt - that could be reversed if desired. You need someone, not me, who understands encryption - RSA comes to mind - and can help you maintain strong encryption over the entire file. I also hope you consider CBC so a 10MB file of all zeroes doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby
To: File Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
Cary
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Can “Counter Mode” be used to encrypt file of size< blocksize with out
changing the file size?
Could you please point me to some example?
Regards
Surendra
-----Original Message-----
From: xxxxx@des.co.uk [mailto:xxxxx@des.co.uk]
Sent: Wednesday, July 17, 2002 2:24 PM
To: File Systems Developers
Subject: [ntfsd] RE: Change file size on NTFS
Hi All,
I often see this question come up and often see poor responses from people
:). Most block ciphers can be used in many different modes, not just the
ones that are randomly pulled out of a hat (normally ECB + CBC). Have you
ever looked at “Counter Mode” this is a modified OFB method that uses an
initialisation vector (IV) + key to generate the next block for encryption.
You can use this mode to encrypt any size buffer/file and simply discard
what you don`t use. Counter Mode also has the ability of random access to
data as block x is not dependent on the successful decryption of block x-1.
There is heaps of information available on this kind of thing. May I suggest
investing in a copy of “Applied Cryptography”. All block cipher modes are
discussed in detail giving pros and cons of each.
Regards
Ben Curley
Data Encryption Systems Ltd.
Website: www.des.co.uk http: / www.deslock.com
http:
-----Original Message-----
From: David J. Craig [mailto:xxxxx@yoshimuni.com]
Sent: 17 July 2002 00:41
To: File Systems Developers
Subject: [ntfsd] RE: Change file size on NTFS
A different encryption algorithm is required. You can’t encrypt files of <
16 bytes with any real security with any algorithm suited for block
encryption. Each 16 byte block contributes to the next block and increases
encryption strength. That is why most encryption algorithms are based upon
512, 2048, or 4096 blocks. There are stream ciphers, but they are a
solution for a different problem.
----- Original Message -----
From: Cary Fu mailto:xxxxx
To: File Systems Developers mailto:xxxxx
Sent: Tuesday, July 16, 2002 6:19 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much. But how does it work when nnnnnnnn < 16?
Cary
----- Original Message -----
From: David mailto:xxxxx J. Craig
To: File Systems Developers mailto:xxxxx
Sent: Tuesday, July 16, 2002 1:26 PM
Subject: [ntfsd] RE: Change file size on NTFS
Let me try a diagram:
[Data nnnnnnnn bytes mod 16] [15 bytes of data]
1. Encrypt the Data nnnnnnnn bytes mod 16 first.
2. Take one byte from the end of the data encrypted in 1. and add to the
front of the 15 byte remainder.
3. Encrypt that 16 byte packet.
4. Write it to the file overlaying the one byte you took out.
5. Do the decryption in reverse order doing the last 16 bytes first and
then the mod 16 pieces of the file.
Do NOT change file size as it just won’t work easily and is not needed for a
general purpose directory based encryption program.
I think you have the filesize available in the FileObject. It is available
from the FSD is you ask.
----- Original Message -----
From: Cary Fu mailto:xxxxx
To: File Systems Developers mailto:xxxxx
Sent: Tuesday, July 16, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you. The step 1 as you mentioned is just what I did. The problem is,
when pagging IO, I don’t have the file size, so, I have to change file size
when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same
experience?
Cary
----- Original Message -----
From: David J. Craig mailto:xxxxx
To: File mailto:xxxxx Systems Developers
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a
file. That can and will create more problems than it solves. Step 1: a
simple solution is to take the last remaining 1-15 bytes and add enough
bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it
again and do it last on encrypt and first on decrypt - that could be
reversed if desired. You need someone, not me, who understands encryption -
RSA comes to mind - and can help you maintain strong encryption over the
entire file. I also hope you consider CBC so a 10MB file of all zeroes
doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby mailto:xxxxx
To: File mailto:xxxxx Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com
mailto:xxxxx
[mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and
decryption on Windows XP NTFS file system. Due to using block cipher (16
bytes long). I need change file size to be 16 bytes boundary. It works
perfect on FAT, but on NTFS, file size after change always being resized by
file system to be 8 bytes boundary. Is there someone happend to know what is
wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks
for any input.
Cary
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I am developing a encryption filter driver and have a question on how to
mark the file as selected for encryption?
I cannot use the file attribute field in the NTFS as it is used by the EFS.
I don’t want to add a header to maintain this information in the file as it
changes the size of file.
Currently I am storing it in system Registry. I know it is not the best way.
Can anyone suggest an alternative method ?
Regards
Surendra
-----Original Message-----
From: David J. Craig [mailto:xxxxx@yoshimuni.com]
Sent: Thursday, July 18, 2002 6:51 PM
To: File Systems Developers
Subject: [ntfsd] RE: Change file size on NTFS
You get what you pay for and are willing to accept. Netscape discovered
that even though they had good algorithms, a minor deficiency in their
random number generator routine made brute force attacks very easy. I want
someone with experience to look at my implementation and see if some mistake
has made the encryption less secure than it should be. If you are using a
toolkit from RSA, you should be able to write something that works well, but
I still want someone else to look unless the toolkit implements all elements
of the algorithm in a fool proof way - if that is even possible!
----- Original Message -----
From: Dan mailto:xxxxx Partelly
To: File Systems Developers mailto:xxxxx
Sent: Wednesday, July 17, 2002 5:21 PM
Subject: [ntfsd] RE: Change file size on NTFS
>> The paging IO requests that are written to the disk are usually in 512
blocks
minimum page size in IA32 architecture is 0x1024.
>> You need to have a consultant from RSA or Counterpane help you with the
algorithms.
What for ? Pay big US$ for a thing which is throughly discussed all over the
NET ? All it takes is reading and a bit of research.
Dan
----- Original Message -----
From: David mailto:xxxxx J. Craig
To: File Systems Developers mailto:xxxxx
Sent: Wednesday, July 17, 2002 10:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
The paging IO requests that are written to the disk are usually in 512
blocks or some multiple of 512. Of course, the file system may not pass all
of the 512 bytes every time, but you might be able to do some investigation
and use that fact. The only problems deal with something copying the file
if the bytes beyond the EOF are needed for decryption. A program that
bypasses the cache with the no cache flag might be a problem. Someone else
suggested learning about encryption algorithms and determine one that will
work in your environment. I know some who like blowfish 448, triple DES,
RC5, and AES. You need to have a consultant from RSA or Counterpane help
you with the algorithms.
----- Original Message -----
From: Cary Fu mailto:xxxxx
To: File Systems Developers mailto:xxxxx
Sent: Wednesday, July 17, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much.
Cary
----- Original Message -----
From: David J. Craig mailto:xxxxx
To: File Systems Developers mailto:xxxxx
Sent: Tuesday, July 16, 2002 4:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
A different encryption algorithm is required. You can’t encrypt files of <
16 bytes with any real security with any algorithm suited for block
encryption. Each 16 byte block contributes to the next block and increases
encryption strength. That is why most encryption algorithms are based upon
512, 2048, or 4096 blocks. There are stream ciphers, but they are a
solution for a different problem.
----- Original Message -----
From: Cary Fu mailto:xxxxx
To: File mailto:xxxxx Systems Developers
Sent: Tuesday, July 16, 2002 6:19 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much. But how does it work when nnnnnnnn < 16?
Cary
----- Original Message -----
From: David J. Craig mailto:xxxxx
To: File mailto:xxxxx Systems Developers
Sent: Tuesday, July 16, 2002 1:26 PM
Subject: [ntfsd] RE: Change file size on NTFS
Let me try a diagram:
[Data nnnnnnnn bytes mod 16] [15 bytes of data]
1. Encrypt the Data nnnnnnnn bytes mod 16 first.
2. Take one byte from the end of the data encrypted in 1. and add to the
front of the 15 byte remainder.
3. Encrypt that 16 byte packet.
4. Write it to the file overlaying the one byte you took out.
5. Do the decryption in reverse order doing the last 16 bytes first and
then the mod 16 pieces of the file.
Do NOT change file size as it just won’t work easily and is not needed for a
general purpose directory based encryption program.
I think you have the filesize available in the FileObject. It is available
from the FSD is you ask.
----- Original Message -----
From: Cary mailto:xxxxx Fu
To: File mailto:xxxxx Systems Developers
Sent: Tuesday, July 16, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you. The step 1 as you mentioned is just what I did. The problem is,
when pagging IO, I don’t have the file size, so, I have to change file size
when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same
experience?
Cary
----- Original Message -----
From: David J. Craig mailto:xxxxx
To: File Systems Developers mailto:xxxxx
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a
file. That can and will create more problems than it solves. Step 1: a
simple solution is to take the last remaining 1-15 bytes and add enough
bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it
again and do it last on encrypt and first on decrypt - that could be
reversed if desired. You need someone, not me, who understands encryption -
RSA comes to mind - and can help you maintain strong encryption over the
entire file. I also hope you consider CBC so a 10MB file of all zeroes
doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby mailto:xxxxx
To: File Systems mailto:xxxxx Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com
mailto:xxxxx
[mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and
decryption on Windows XP NTFS file system. Due to using block cipher (16
bytes long). I need change file size to be 16 bytes boundary. It works
perfect on FAT, but on NTFS, file size after change always being resized by
file system to be 8 bytes boundary. Is there someone happend to know what is
wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks
for any input.
Cary
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Yes it can be used to encrypt any length of file. If you are new to
encryption I can recommend “Applied Cryptography” (as I mentioned before) or
check out
http://www.eskimo.com/~weidai/cryptlib.html
http:
This is an excellent crypto library that covers just about everything you
will ever want to do. You will need to play around with the source to get it
to work in kernel mode though.
If you understand block ciphers though, and the various feedback modes, it
isnt hard to implement your own code using the reference code of the chosen<br>algorithm as a guide.<br><br>Ben Curley<br>Data Encryption Systems Ltd.<br><br>-----Original Message-----<br>From: SurendraI [mailto:xxxxx@esntechnologies.co.in] <br>Sent: 18 July 2002 14:52<br>To: File Systems Developers<br>Subject: [ntfsd] RE: Change file size on NTFS<br><br>Can "Counter Mode" be used to encrypt file of size< blocksize with out<br>changing the file size?<br>Could you please point me to some example?<br><br>Regards<br>Surendra<br>-----Original Message-----<br>From: xxxxx@des.co.uk [mailto:xxxxx@des.co.uk]<br>Sent: Wednesday, July 17, 2002 2:24 PM<br>To: File Systems Developers<br>Subject: [ntfsd] RE: Change file size on NTFS<br><br>Hi All,<br><br>I often see this question come up and often see poor responses from people<br>:). Most block ciphers can be used in many different modes, not just the<br>ones that are randomly pulled out of a hat (normally ECB + CBC). Have you<br>ever looked at "Counter Mode" this is a modified OFB method that uses an<br>initialisation vector (IV) + key to generate the next block for encryption.<br>You can use this mode to encrypt any size buffer/file and simply discard<br>what you dont use. Counter Mode also has the ability of random access to
data as block x is not dependent on the successful decryption of block x-1.
There is heaps of information available on this kind of thing. May I suggest
investing in a copy of “Applied Cryptography”. All block cipher modes are
discussed in detail giving pros and cons of each.
Regards
Ben Curley
Data Encryption Systems Ltd.
Website: www.des.co.uk http: / www.deslock.com
http:
-----Original Message-----
From: David J. Craig [mailto:xxxxx@yoshimuni.com]
Sent: 17 July 2002 00:41
To: File Systems Developers
Subject: [ntfsd] RE: Change file size on NTFS
A different encryption algorithm is required. You can’t encrypt files of <
16 bytes with any real security with any algorithm suited for block
encryption. Each 16 byte block contributes to the next block and increases
encryption strength. That is why most encryption algorithms are based upon
512, 2048, or 4096 blocks. There are stream ciphers, but they are a
solution for a different problem.
----- Original Message -----
From: Cary Fu mailto:xxxxx
To: File Systems Developers mailto:xxxxx
Sent: Tuesday, July 16, 2002 6:19 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much. But how does it work when nnnnnnnn < 16?
Cary
----- Original Message -----
From: David J. Craig mailto:xxxxx
To: File Systems Developers mailto:xxxxx
Sent: Tuesday, July 16, 2002 1:26 PM
Subject: [ntfsd] RE: Change file size on NTFS
Let me try a diagram:
[Data nnnnnnnn bytes mod 16] [15 bytes of data]
1. Encrypt the Data nnnnnnnn bytes mod 16 first.
2. Take one byte from the end of the data encrypted in 1. and add to the
front of the 15 byte remainder.
3. Encrypt that 16 byte packet.
4. Write it to the file overlaying the one byte you took out.
5. Do the decryption in reverse order doing the last 16 bytes first and
then the mod 16 pieces of the file.
Do NOT change file size as it just won’t work easily and is not needed for a
general purpose directory based encryption program.
I think you have the filesize available in the FileObject. It is available
from the FSD is you ask.
----- Original Message -----
From: Cary Fu mailto:xxxxx
To: File mailto:xxxxx Systems Developers
Sent: Tuesday, July 16, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you. The step 1 as you mentioned is just what I did. The problem is,
when pagging IO, I don’t have the file size, so, I have to change file size
when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same
experience?
Cary
----- Original Message -----
From: David J. Craig mailto:xxxxx
To: File mailto:xxxxx Systems Developers
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a
file. That can and will create more problems than it solves. Step 1: a
simple solution is to take the last remaining 1-15 bytes and add enough
bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it
again and do it last on encrypt and first on decrypt - that could be
reversed if desired. You need someone, not me, who understands encryption -
RSA comes to mind - and can help you maintain strong encryption over the
entire file. I also hope you consider CBC so a 10MB file of all zeroes
doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby mailto:xxxxx
To: File mailto:xxxxx Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com
mailto:xxxxx
[mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and
decryption on Windows XP NTFS file system. Due to using block cipher (16
bytes long). I need change file size to be 16 bytes boundary. It works
perfect on FAT, but on NTFS, file size after change always being resized by
file system to be 8 bytes boundary. Is there someone happend to know what is
wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks
for any input.
Cary
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MessageThank you for these information.
Cary
----- Original Message -----
From: xxxxx@des.co.uk
To: File Systems Developers
Sent: Thursday, July 18, 2002 7:23 AM
Subject: [ntfsd] RE: Change file size on NTFS
Yes it can be used to encrypt any length of file. If you are new to encryption I can recommend “Applied Cryptography” (as I mentioned before) or check out
http://www.eskimo.com/~weidai/cryptlib.html
This is an excellent crypto library that covers just about everything you will ever want to do. You will need to play around with the source to get it to work in kernel mode though.
If you understand block ciphers though, and the various feedback modes, it isn`t hard to implement your own code using the reference code of the chosen algorithm as a guide.
Ben Curley
Data Encryption Systems Ltd.
-----Original Message-----
From: SurendraI [mailto:xxxxx@esntechnologies.co.in]
Sent: 18 July 2002 14:52
To: File Systems Developers
Subject: [ntfsd] RE: Change file size on NTFS
Can “Counter Mode” be used to encrypt file of size< blocksize with out changing the file size?
Could you please point me to some example?
Regards
Surendra
-----Original Message-----
From: xxxxx@des.co.uk [mailto:xxxxx@des.co.uk]
Sent: Wednesday, July 17, 2002 2:24 PM
To: File Systems Developers
Subject: [ntfsd] RE: Change file size on NTFS
Hi All,
I often see this question come up and often see poor responses from people :). Most block ciphers can be used in many different modes, not just the ones that are randomly pulled out of a hat (normally ECB + CBC). Have you ever looked at “Counter Mode” this is a modified OFB method that uses an initialisation vector (IV) + key to generate the next block for encryption. You can use this mode to encrypt any size buffer/file and simply discard what you don`t use. Counter Mode also has the ability of random access to data as block x is not dependent on the successful decryption of block x-1.
There is heaps of information available on this kind of thing. May I suggest investing in a copy of “Applied Cryptography”. All block cipher modes are discussed in detail giving pros and cons of each.
Regards
Ben Curley
Data Encryption Systems Ltd.
Website: www.des.co.uk / www.deslock.com
-----Original Message-----
From: David J. Craig [mailto:xxxxx@yoshimuni.com]
Sent: 17 July 2002 00:41
To: File Systems Developers
Subject: [ntfsd] RE: Change file size on NTFS
A different encryption algorithm is required. You can’t encrypt files of < 16 bytes with any real security with any algorithm suited for block encryption. Each 16 byte block contributes to the next block and increases encryption strength. That is why most encryption algorithms are based upon 512, 2048, or 4096 blocks. There are stream ciphers, but they are a solution for a different problem.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 6:19 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you very much. But how does it work when nnnnnnnn < 16?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Tuesday, July 16, 2002 1:26 PM
Subject: [ntfsd] RE: Change file size on NTFS
Let me try a diagram:
[Data nnnnnnnn bytes mod 16] [15 bytes of data]
Do NOT change file size as it just won’t work easily and is not needed for a general purpose directory based encryption program.
I think you have the filesize available in the FileObject. It is available from the FSD is you ask.
----- Original Message -----
From: Cary Fu
To: File Systems Developers
Sent: Tuesday, July 16, 2002 12:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
Thank you. The step 1 as you mentioned is just what I did. The problem is, when pagging IO, I don’t have the file size, so, I have to change file size when IRP_MJ_CLOSE and IRP_MJ_SET_INFORMATION. Anyone happends to have same experience?
Cary
----- Original Message -----
From: David J. Craig
To: File Systems Developers
Sent: Monday, July 15, 2002 12:13 PM
Subject: [ntfsd] RE: Change file size on NTFS
I would suggest that no encryption of a general purpose modify the size of a file. That can and will create more problems than it solves. Step 1: a simple solution is to take the last remaining 1-15 bytes and add enough bytes from the block before it to make it 16 bytes. Encrypt/Decrypt it again and do it last on encrypt and first on decrypt - that could be reversed if desired. You need someone, not me, who understands encryption - RSA comes to mind - and can help you maintain strong encryption over the entire file. I also hope you consider CBC so a 10MB file of all zeroes doesn’t show a repeating pattern.
----- Original Message -----
From: Jamey Kirby
To: File Systems Developers
Sent: Monday, July 15, 2002 1:41 PM
Subject: [ntfsd] RE: Change file size on NTFS
It must be sector aligned (512)
-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Cary Fu
Sent: Monday, July 15, 2002 10:00 AM
To: File Systems Developers
Subject: [ntfsd] Change file size on NTFS
HI all,
I am developing a file system filter driver doing fly encryption and decryption on Windows XP NTFS file system. Due to using block cipher (16 bytes long). I need change file size to be 16 bytes boundary. It works perfect on FAT, but on NTFS, file size after change always being resized by file system to be 8 bytes boundary. Is there someone happend to know what is wrong here? How can I change file size to 16 bytes boundary on NTFS. Thanks for any input.
Cary
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