Peter Fairbrother wrote: > If the channel is authentic then a MitM is hard - but not impossible. The > "no-cloning" theorem is all very well, but physics actually allows imperfect > cloning of up to 5/6 of the photons while retaining polarisation, and this > should be allowed for as well as the noise calculations. I don't know of any > existing OTS equipment that does that. > > A lasing medium can in theory clone photons with up to 5/6 of them retaining > enough polarisation data to use as above, though in practice the noise is > usually high. > > There is also another less noisy cloning technique which has recently been > done in laboratories, though it doubles the photon's wavelength, which would > be noticeable, and I can't see ofhand how in practice to half the wavelength > again without losing polarisation (except perhaps using changing > gravitational fields and the like); but there is no theory that says that > that can't be done.
Had two requests for links (and some scepticism) about this already. Try: http://www.photonics.com/spectra/research/XQ/ASP/preaid.44/QX/read.htm for an article and some ref's (though I'm not even sure if the paper referred to is the one I'm thinking of, the one with wavelength doubling. I though it was published earlier this year). I'll try and post some better links later. -- Peter Fairbrother --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]