[E-Lang] Quantum computing and capabilities

[hal@finney.org]

At 02:01 PM 1/31/01 -0500, Ralph Hartley wrote:
> What would be the effect of quantum computation on the basic design of
> security systems? It is clear that the effect would be substantial, but
> would it be total? That is, could old principles and designs still be
> used, with relatively small changes to block new threats and exploit new
> possibilities, or would you have to basically start over from scratch?
> Is the design of E one that would survive?

Quantum computers theoretically could break the public key cryptosystems
in use today.  There are systems based on coding theory and other
problems which would apparently not be broken, but they have not been
very heavily analyzed.  However symmetric crypto is not hampered much
by quantum computers; you just need to use keys twice as long.  256 bit
AES will be secure even if quantum computers come into existence.

Looking at the Granovetter diagram at
http://www.erights.org/elib/capability/ode/index.html, I wonder how
much E needs public key cryptography?  Could it get by with only
symmetric crypto, with symmetric keys embedded in the capabilities?

We would assume that all parties who are initially in communication start
off sharing keys.  Then when Alice passes Bob a capability to Carol,
this will give him a secret key that he can use in talking to Carol,
the same secret key Alice shared with Carol.

This would mean that Bob cannot set up a secure channel to Carol that
Alice cannot monitor, but I believe this is OK, as the security properties
of capabilities do not allow him to establish such a channel.

How far can we get in E with only symmetric crypto?

Hal