Re: Toshiba Quantum Key Server System

From: Alan (a__l__a__n_at_hotmail.com)
Date: 05/02/05 

Date: Mon, 2 May 2005 15:05:37 -0400

"Timoleon wrote:
>
> http://news.bbc.co.uk/2/hi/science/nature/4496893.stm
>
> Any implications for general cryptographic security?

Quantum cryptography does not in any way reduce the strength of conventional
cryptography. You may be thinking of quantum computing, which theoretically
could have a major impact, but is many years from feasibility.

Quantum cryptography enables secure transfer of an encryption key from
sender to receiver, assuming that effective authentication occurs during the
key exchange. If that key is used as a one-time pad to encrypt a plaintext
message, then it would be theoretically impossible for an evesdropper to
derive the plaintext by observing the resulting ciphertext. OTOH it would
be possible to flip bits in the ciphertext to alter the received plaintext,
unless effective integrity checking is also used.

So quantum cryptography may eliminate one weakness in encrypted
communication. Authentication and message integrity must be addressed using
conventional techniques, with whatever caveats apply to those techniques.

Alan

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