Lecture Notes in Computer Science 5185

24 S. Choi et al.
Table 1. Performance of Measurement and Verification (in sec)
Target Size Measurement Verification RIM Cert
ld-linux.so 115668, 72004 0.02 0.41 0.40
libm.so 780380, 442164 0.1 0.41 0.40
libssl.so 217324, 126848 0.03 0.42 0.40
libnss files.so 54324, 28032 0.00 0.42 0.40
wlanconfig 74720, 45304 0.01 0.43 0.40
tcsd 314032, 111756 0.04 0.41 0.40
attestation agent 76440, 41632 0.01 0.42 0.40
busybox 358536, 276312 0.05 0.43 0.40
The first number in the field of Size is the entire file size and the second one
is the size of text and data segments. RIM Cert field represents the time taken
from sending request of RIM Cert Verification and Extend to the MTM board
to getting the response from it. Each figure is the average time of running a
test 10 times using the do gettimeofday() function supported in Linux Kernel.
The delay by verification is almost static and most of the delay comes from
RIM Cert Verification and Extend. The signature verification with RSA 2048
public key and relatively slow data transmission speed of I 2 C may contribute
to the delay. The overhead due to measurement grows with the size of text and
data segments as the input for hash operation increases. Our experiment shows
that the initial loading of executables or libraries can be delayed up to 0.51 sec
and this overhead decreases to less than or equal to 0.1 sec with the introduction
of cache, since no verification is required. libm.so is one of the large libraries in
embedded Linux and the loading of it with cache takes 0.1 sec thus we believe
that the overhead shown is not critical.
We also perform an experimentation to assess the time taken for attestation.
The system for running Privacy CA and Challenger is the IBM ThinkPad
notebook which uses an Intel CPU running at 2 GHz and has 2 GB RAM. Privacy
CA and Challenger communicate with DMB device in the same subnet
over wireless LAN. Table 2 summarizes the performance of attestation with 4
measurement entries in ML and 14 measurement entries in ML. Each tests is
conducted 10 times and the result is the average of them. The meaning of each
fields is as follows: Attestation: the entire time taken for attestation, Client:
preparing attestation response message at mobile device, Quote: retrieving a
Quote message from a MTM, OIAP: creation of authorization session with a
MTM using Object-Independent Authorization Protocol (OIAP) , Challenge:
Table 2. Performance of Attestation (in sec)
Attestation Client Quote OIAP Challenge Verification
4entries 1.9416 1.63 0.856 0.36 0.0461 0.006
14 entries 1.9908 1.63 0.856 0.36 0.0497 0.0062