bitlocker does diffuser work

How does the diffuser work under BitLocker encryption?
Is the diffuser applied to each block of cyphertext within a sector, or is it somehow applied across several blocks concurrently or across the entire sector at once, some how?
I'm assuming that for an AES-256 bit key, BitLocker encrypts the entire 512-byte sector using 32-byte blocks of data. The Cypher Block Chaining (CBC), XOR's the cyphertext output of the previous block with the plaintext of the current block. How is diffusion applied, and how is the diffuser generated?
Some nice references on good ol' wikipedia: http://en.wikipedia.org/wiki/Confusion_and_diffusion http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation
Thanks!

Tavis, you keep firing good questions at me :)
The FVEK (Full Volume Encryption Key) contains 2 keys, one for the AES algorithm, and one for the Diffuser algorithm. This ensures the diffuser cannot weaken AES (a shared key would be an architecture concern). The diffuser is applied to an entire sector before encryption and can be described as "mixing the bits of the sector prior to encryption". The IV (initial vector) for both algorithms is derived from the sector number to ensure that sectors cannot be swapped.
Consider this in reverse, a single bit change will result in a moderate change c/o CBC, however this change gets diffused throughout all the bits of the sector resulting in an entire sector change. This mitigates creative attacks where someone would try to introduce a minor change into some code or data to change OS behavior in a desirable way.
A paper giving the details of the Diffuser (and other low level details) is forthcoming, before RTM. - Jamie Hunter [MS]
"tavis" wrote in message

How does the diffuser work under BitLocker encryption?
Is the diffuser applied to each block of cyphertext within a sector, or is it somehow applied across several blocks concurrently or across the entire sector at once, some how?
I'm assuming that for an AES-256 bit key, BitLocker encrypts the entire 512-byte sector using 32-byte blocks of data. The Cypher Block Chaining (CBC), XOR's the cyphertext output of the previous block with the plaintext of the current block. How is diffusion applied, and how is the diffuser generated?
Some nice references on good ol' wikipedia: http://en.wikipedia.org/wiki/Confusion_and_diffusion http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation
Thanks!

Hi Jamie,
Has the paper you mention below providing details of Diffuser and the overall encryption algorithm available yet?
If not, a question: Can you describe a bit more about how a 256-bit AES key is used to "mix up the bits" (all 512 bytes) of an *entire* sector, when the key itself is only 32 bytes long?
Thanks!
"Jamie Hunter [MS]" wrote:

Tavis, you keep firing good questions at me :)
The FVEK (Full Volume Encryption Key) contains 2 keys, one for the AES algorithm, and one for the Diffuser algorithm. This ensures the diffuser cannot weaken AES (a shared key would be an architecture concern). The diffuser is applied to an entire sector before encryption and can be described as "mixing the bits of the sector prior to encryption". The IV (initial vector) for both algorithms is derived from the sector number to ensure that sectors cannot be swapped.
Consider this in reverse, a single bit change will result in a moderate change c/o CBC, however this change gets diffused throughout all the bits of the sector resulting in an entire sector change. This mitigates creative attacks where someone would try to introduce a minor change into some code or data to change OS behavior in a desirable way.
A paper giving the details of the Diffuser (and other low level details) is forthcoming, before RTM. - Jamie Hunter [MS]
"tavis" wrote in message How does the diffuser work under BitLocker encryption?
Is the diffuser applied to each block of cyphertext within a sector, or is it somehow applied across several blocks concurrently or across the entire sector at once, some how?
I'm assuming that for an AES-256 bit key, BitLocker encrypts the entire 512-byte sector using 32-byte blocks of data. The Cypher Block Chaining (CBC), XOR's the cyphertext output of the previous block with the plaintext of the current block. How is diffusion applied, and how is the diffuser generated?
Some nice references on good ol' wikipedia: http://en.wikipedia.org/wiki/Confusion_and_diffusion http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation
Thanks!