![](bg6.png)
Figure 6: Memory Access.
coefficients and ciphers are also shown in that figure.
5 OPEN ISSUES & FUTURE
WORK
The environmentpresented in this paper has proof-of-
concept capabilities and a dependency between mem-
ory size and performance, which makes it suitable for
small problem sizes. By extending the capabilities of
our concept to interact with the host system, we will
be able to perform calculations on portions of secret
data or secret algorithms, that are part of a larger sys-
tem. It is possible to inject encrypted data into the
encrypted environment, which is sufficient to receive
process data from outside the cipher-space. However,
this induces further problems, like the correctness and
consistency of the encrypted code and data. A pos-
sible field of application is Cloud Computing, where
small- and medium-scale compute jobs are performed
which have high privacy requirements. The estab-
lishment of an appropriate system- and application-
architecture will be the key to integrate our concept
into existing cloud applications and environments, to
face new security requirements of mobile code and
distributed applications.
6 SUMMARY
In this paper we presented the first method to per-
form the execution of arbitrary encrypted programs,
operating on encrypted data. In contrast to other so-
lutions, the code as well as the processed data, held
entirely in the cipher-space, still remain dynamic and
can be provided with data after having been transmit-
ted to the executing host. We described a method to
represent circuits by means of homomorphically en-
crypted arithmetics. Applying the basic logic func-
tion representations, we sketched how to build dif-
ferent microprocessor primitives, like memory-access
logic and arithmetic operations. We then developed
a simple CPU- and system-model and presented the
reference implementation of our model on top of the
Smart-Gentry encryption scheme. An analysis deter-
mined the relationship between our system model and
the underlying encryption scheme. We provided per-
formance figures for different key sizes and showed
that our system is suitable to act as a sound basis for
further empirical investigation of applied homomor-
phic encryption.
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