At 10:18 PM +0000 9/13/03, David Wagner wrote:
One could reasonably ask how often it is in practice that we have a
physical channel whose authenticity we trust, but where eavesdropping
is a threat.  I don't know.

I think there is another problem with quantum cryptography. Putting aside the question of the physical channel, there is the black box at either end that does all this magical quantum stuff. One has to trust that black box.

- Its design has to thoroughly audited and the integrity of each unit verified

- It has to be shipped securely from some factory or depot to each end point

- It has to be continuously protected from tampering.

It seems to me one could just as well ship a 160 GB hard drive filled with random keying material to each endpoint. The disk drive would receive the same level of physical security as the quantum black boxes. At one AES256 key per second, a 160GB hard drive holds 150 years of keying material. For forward security one can erase used keys. (If you don't trust disk erasing, ship a carton of CD-Rs or DVD-Rs and burn them as they are used up).

The 160 GB hard drive has a couple of advantages over quantum key exchange:

- No special assumptions about the channel are needed. One can use the existing Internet, telephone, satellite and even shortwave infrastructure.

- The hard drives and the PCs to use with them can be purchased off the shelf from a random computer store. No one is alerted that you are engaging in secret communications so no one is likely to tamper with your equipment before you get it.

- The necessary software is easy to write and audit

- I expect a quantum crypto box to cost far more than a160 GB disk drive, not to mention the cost of the dedicated fiber channel.

What am I missing?

Arnold Reinhold

The Cryptography Mailing List
Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]

Reply via email to