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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 742
CHAP. 9
PROBLEMS
711
52.
Section 9.10.1 describes a set of firewall rules that limit outside access to only three
services. Describe another set of rules that you can add to this firewall to further
restrict access to these services.
53.
On some machines, the
SHR
instruction used in Fig. 9-38(b) fills the unused bits with
zeros; on others the sign bit is extended to the right. For the correctness of Fig. 9-38(b),
does it matter which kind of shift instruction is used?
If so, which is better?
54.
To verify that an applet has been signed by a trusted vendor, the applet vendor may in-
clude a certificate signed by a trusted third party that contains its public key. However,
to read the certificate, the user needs the trusted third party’s public key. This could be
provided by a trusted fourth party, but then the user needs that public key.
It appears
that there is no way to bootstrap the verification system, yet existing browsers use it.
How could it work?
55.
Describe three features that make Java a better programming language than C to write
secure programs.
56.
Assume that your system is using JDK 1.2. Show the rules (similar to those in Figure
9-40) you will use to allow an applet from
www.appletsRus.com
to run on your ma-
chine. This applet may download additional files from
www.appletsRus.com
, read/write
files in
/usr/tmp/
, and also read files from
/usr/me/appletdir
.
57.
How are applets different from applications? How does this difference relate to secu-
rity?
58.
Write a pair of programs, in C or as shell scripts, to send and receive a message by a
covert channel on a UNIX system.
(
Hint
: A permission bit can be seen even when a
file is otherwise inaccessible, and the
sleep
command or system call is guaranteed to
delay for a fixed time, set by its argument.) Measure the data rate on an idle system.
Then create an artificially heavy load by starting up numerous different background
processes and measure the data rate again.
59.
Several UNIX systems use the DES algorithm for encrypting passwords. These sys-
tems typically apply DES 25 times in a row to obtain the encrypted password. Down-
load an implementation of DES from the Internet and write a program that encrypts a
password and checks if a password is valid for such a system.
Generate a list of 10 en-
crypted passwords using the Morris-Thomson protection scheme.
Use 16-bit salt for
your program.
60.
Suppose a system uses ACLs to maintain its protection matrix.
Write a set of man-
agement functions to manage the ACLs when (1) a new object is created; (2) an object
is deleted; (3) a new domain is created; (4) a domain is deleted; (5) new access rights
(a combination of
r
,
w
,
x
) are granted to a domain to access an object; (6) existing ac-
cess rights of a domain to access an object are revoked; (7) new access rights are grant-
ed to all domains to access an object; (8) access rights to access an object are revoked
from all domains.
61.
Implement the program code outlined in Sec. 9.7.1 to see what happens when there is
buffer overflow. Experiment with different string sizes.
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