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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 738
CHAP. 9
PROBLEMS
707
10.
Modify the ACL from the previous problem for one file to grant or deny an access that
cannot be expressed using the UNIX
rwx
system. Explain this modification.
11.
Suppose there are four security levels, 1, 2 and 3.
Objects
A
and
B
are at level 1,
C
and
D
are at level 2, and
E
and
F
are at level 3.
Processes 1 and 2 are at level 1, 3 and
4 are at level 2, and 5 and 6 are at level 3.
For each of the following operations, spec-
ify whether they are permissible under Bell-LaPadula model, Biba model, or both.
(a) Process 1 writes object
D
(b) Process 4 reads object
A
(c) Process 3 reads object
C
(d) Process 3 writes object
C
(e) Process 2 reads object
D
(f) Process 5 writes object
F
(g) Process 6 reads object
E
(h) Process 4 write object
E
(i) Process 3 reads object
F
12.
In the Amoeba scheme for protecting capabilities, a user can ask the server to produce
a new capability with fewer rights, which can then be given to a friend. What happens
if the friend asks the server to remove even more rights so that the friend can give it to
someone else?
13.
In Fig. 9-11, there is no arrow from process
B
to object
1
.
Would such an arrow be al-
lowed? If not, what rule would it violate?
14.
If process-to-process messages were allowed in Fig. 9-11, what rules would apply to
them? For process
B
in particular, to which processes could it send messages and
which not?
15.
Consider the steganographic system of Fig. 9-14. Each pixel can be represented in a
color space by a point in the three-dimensional system with axes for the R, G, and B
values. Using this space, explain what happens to the color resolution when steganog-
raphy is employed as it is in this figure.
16.
Break the following monoalphabetic cipher. The plaintext, consisting of letters only, is
a well-known excerpt from a poem by Lewis Carroll.
kfd ktbd fzm eubd kfd pzyiom mztx ku kzyg ur bzha kfthcm
ur mfudm zhx mftnm zhx mdzythc pzq ur ezsszcdm zhx gthcm
zhx pfa kfd mdz tm sutythc fuk zhx pfdkfdi ntcm fzld pthcm
sok pztk z stk kfd uamkdim eitdx sdruid pd fzld uoi efzk
rui mubd ur om zid uok ur sidzkf zhx zyy ur om zid rzk
hu foiia mztx kfd ezindhkdi kfda kfzhgdx ftb boef rui kfzk
17.
Consider a secret-key cipher that has a 26
×
26 matrix with the columns headed by
ABC ... Z
and the rows also named
ABC ... Z
.
Plaintext is encrypted two characters at a
time. The first character is the column; the second is the row. The cell formed by the
intersection of the row and column contains two ciphertext characters. What constraint
must the matrix adhere to and how many keys are there?
18.
Consider the following way to encrypt a file. The encryption algorithm uses two
n
-byte
arrays,
A
and
B
.
The first
n
bytes are read from the file into
A
. Then
A
[0] is copied to
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