age,” a paper published earlier this
year, researchers Seny Kamara and
Kristin Lauter of Microsoft Research
described a virtual private storage service that aims to provide the security
of a private cloud and the cost savings
of a public cloud. Data in the cloud
remains encrypted, and hence protected from the cloud provider, court
subpoenas, and the like. Users index
their data, then upload the data and
the index, which are both encrypted, to
the cloud. As needed, users can generate tokens and credentials that control
who has access to what data.
Given a token for a keyword, an
authorized user can retrieve pointers to the encrypted files that contain
the keyword, and then search for and
download the desired data in encrypted form. Unauthorized observers can’t
know anything useful about the files or
The experimental Microsoft service
also offers users “proof of storage,” a
protocol by which a server can prove to
a client that it did not tamper with its
encrypted data. The client encodes the
data before uploading it and can verify
the data’s integrity at will.
Not all cloud security risks arise
from technology, says Radu Sion, a
computer science professor at Stony
Brook University. There is scant legal or regulatory framework, and few
precedents, to deal with issues of liability among the parties in cloud arrangements, he notes. “What happens
Kamara and Kristin
a virtual private
storage service that
provides the security
of a private cloud
and the cost savings
of a public cloud.
when your data is on a server in China
but you outsourced to a cloud service
in New York?” asks Sion. “Or what if
you have the legal resources to fight a
subpoena for your data, but they sub-
poena your cloud provider instead?
You will be under scrutiny for moving
to the cloud by your shareholders and
Nevertheless, Sion says all but the
most sophisticated enterprises will
be safer putting their computing re-
sources in the expert hands of one of
the major cloud providers. “Compa-
nies like Google and Amazon and Mi-
crosoft have hundreds of people de-
voted to security,” he says. “How many
do you have?”
Christodorescu, M., Sailer, R., Schales, D.,
Sgandurra, D., and Zamboni, D.
Cloud security is not (just) virtualization
security, Proceedings of the 2009 ACM
Workshop on Cloud Computing Security,
Chicago, IL, nov. 13, 2009.
Fully homomorphic encryption using ideal
lattices, Proceedings of the 41st Annual
ACM Symposium on Theory of Computing,
Bethesda, MD, May 31–June 2, 2009.
Kamara, S. and Lauter, K.
Cryptographic cloud storage, Proceedings
of Financial Cryptography: Workshop on
Real-Life Cryptographic Protocols and
Standardization, Tenerife, Canary Islands,
Spain, January 25–28, 2010.
Ristanpart, T., Tromer, E., Sacham, H.,
and Savage, S.
hey, you, get off of my cloud: exploring
information leakage in third-party
compute clouds, Proceedings of the
16th ACM Conference on Computer and
Communications Security, Chicago, IL,
nov. 9–13, 2009.
Shi, E., Bethencourt, J., Chan, T-H., Song, D.,
and Perrig, A.
Multi-dimensional range query over
encrypted data, Computer Science
Technical Report CMU-CS-06-135R,
Carnegie Mellon University, March 2007.
Gary Anthes is a technology writer and editor based in
© 2010 acm 0001-0782/10/1100 $10.00
Math at Web Speed
“Many hands make light work,”
goes the old adage. Now there’s
data to prove it.
In recent weeks, both yahoo!
and google have announced the
results of separate mathematical
experiments that demonstrate
the computational power of large
clusters of networked PCs.
at yahoo!, a team led by
researcher Tsz-Wo Sze broke
the world record for calculating
the digits of pi, crunching the
famously irrational number
to the two-quadrillionth bit by
stitching together more than
1,000 computers to complete the
calculation over a 23-day period.
The researchers estimate that
a typical computer would have
taken at least 500 years to carry
out the same operation.
another group of researchers
recently took advantage of
google’s distributed computing
infrastructure to tackle another
famously thorny computational
challenge: rubik’s Cube. The
team developed an algorithm
capable of solving any rubik’s
Cube configuration in 20
moves or less, resolving a
conundrum that has puzzled
mathematicians for three
decades. The computers
simulated all 43 quintillion
possible combinations of the
cube in just a few weeks, a task
the researchers estimate would
have taken a single computer
google has yet to release the
details of its technical solution,
but it probably bears some
resemblance to the approach
used at yahoo!, where the team
used apache hadoop, open-source software originally
developed at google (and later
developed extensively by yahoo!)
that allows developers to stitch
together thousands of computers
over the network into a powerful
“We believe that our hadoop
clusters are already more
powerful than many other
supercomputers,” says Sze, who
conceived of the project as part
of an internal yahoo! contest to
demonstrate the capabilities of
In both cases, the
mathematical problems proved
particularly well-suited to
distributed computing because
the calculations can be parceled
out over the network into much
smaller operations, capable of
running on a standard-issue PC.
Making light work indeed.