On Fri, 28 Jan 1994, Yaroslav Faybishenko wrote:

i assume the message would be translated in blocks (instead of in a stream), and then those blocks would be compared to verify that no one is eavesdropping. So, if there is actually someone eavesdropping, then the very first block that is transmitted would be corrupt, so when Alice and Bob compare their versions of the block, they would discover that the channel is insecure, so they would stop the conversation.

I believe here you are kind of describing the private channel (the quantum channel) though I've never heard of it described in quite this way. When I refer to the Public Channel, I am referring to the channel that Alice and Bob talk on so that they may compare the blocks or bits that they have both received. Hence, a powerful enough Eve could insert herself in the private channel (this is very much discussed) as well as the public channel (which I haven't seen addressed.) Many of the papers discuss Eve inserting herself in the private channel and impersonating Alice (to Bob), and Bob (to Alice), but this results in a non-correlation of the measurements when compared over the public channel. But if Eve may impersonate both people on _both_ channels it may be possible to dupe Alice and Bob. I expect what is important is the definition of what a public channel is? (Still haven't got access to my original thoughts on this, will say more later.) Regards, Joseph M. Reagle Jr. | reagle@umbc.edu | It is a good day to die! --Worf. jreagl1@umbc8.umbc.edu |