It's more likely that the NSA has devoted its efforts to key capture
and side-channel attacks rather than brute-forcing its way through
ciphertext en masse - but it's also true that our crypto maths won't
last forever.
Which draws attention to projects like
this one (PDF), which is looking at protection of multi-party computation (MPC) activities.
According to
Phys.org:
“The idea behind Multi-Party Computation is that it should enable two
or more people to compute any function of their choosing on their secret
inputs, without revealing their inputs to either party. One example is
an election; voters want their vote to be counted but they do not want
their vote made public.”
As
The Register understands the
system, this might also be useful in cloud-based collaboration, since it
would protect Average Joe's data against the rest of the world,
including Average Joe's boss, if it so happened that her machine were
compromised.
The aim of the work by a UK-Danish collaboration is
to strap the supercharger onto a protocol called SPDZ – pronounced
Speedz – to give it real-world performance.
In SPDZ, two machines
working on a multi-party computation problem can do so without revealing
their data to each other. They describe SPDZ as: “secure against active
static adversaries in the standard model, is actively secure, and
tolerates corruption of
n-1 of the
n parties. The SPDZ
protocol follows the preprocessing model: in an offline phase some
shared randomness is generated, but neither the function to be computed
nor the inputs need be known; in an online phase the actual secure
computation is performed.”
Let's unpick this a little. The claims
of security aren't remarkable, and the protocol is designed so that your
data will remain secure even if everybody else is compromised (“
n-1 of the
n parties”).
The
protocol relies on a message authentication code (MAC, just to make
sure there's a confusion with Media Access Control) – and this made it
computationally demanding. The MAC is partly shared between the parties,
and parties had to reveal their shares of the code to communicate.
The
problem with this is that revealing the code meant for every
communication it had to be renegotiated – hence its slow performance.
Other issues were that key generation was also demanding, covert
security was considered weak, and the proposed new system is more secure
“in the offline phase”.
The system as a whole is
described on Slashdot this way:
“MPC
is similar in concept to the “zero knowledge proof” – a set of rules
that would allow parties on one end of a transaction to verify that they
know a piece of information such as a password by offering a different
piece of information that could be known only to the other party. The
technique could allow secure password-enabled login without requiring
users to type in a password or send it across the Internet. Like many
other attempts at MPC, however, SPDZ was too slow and cumbersome to be
practical.”
If the paper – which will be presented at this week's
ESORICS 2013 conference – holds up, it'll eventually add a new string to
the bow of those that want to protect information, rather than snoop on
it. ®