can you please answer these two questions !! fall answer, please !! 1. Show that

Question

can you please answer these two questions !! fall answer, please !!

1. Show that if longitudinal parity is used as an error detection code, values in a database can still be modified without detection. (Longitudinal parity is computed for the nth bit of each byte; that is, one parity bit is computed and retained for all bits in the 0th position, another parity bit for all bits in the 1st position, etc.)

2. Disclosure of the sum of all financial aid for students in Smith dorm is not sensitive because no individual student is associated with an amount. Similarly, a list of names of students receiving financial aid is not sensitive because no amounts are specified. However, the combination of these two lists reveals the amount for an individual student if only one student in Smith dorm receives aid. What computation would a database management system have to perform to determine that the list of names might reveal sensitive data? What records would the database management system have to maintain on what different users know in order to determine that the list of names might reveal sensitive data?

Explanation / Answer

Another approach to deskewing is to consider the bit stream as a sequence of

non-overlapping groups of n bits each and output the parity of each group.That is,

if a group contains an odd number of ones, the output is 1; otherwise the output

is 0.

a. Express this operation in terms of a basic Boolean function.

THE ANSWER IS the input bits s1,s2, ....,sn and the output bits o as o = s1 + s2, .... sn

b. Assume that the probability of a 1 is 0.5 . If each group consists of 2 bits, what is the probability of an output of 1?

THE ANSWER IS 0.5- 2^2

c. If each group consists of 4 bits, what is the probability of an output of 1? THE ANSWER IS 0.5- 8^4

d. Generalize the result to find the probability of an output of 1 for input groups of n bits. The limit as n goes to infinity is 0.5

First we arrange the packet in a rectangular fashion as such:
1110 1011
1001 1101
Next we calculate the row and column even parity bits.
The even parity bit is 0 if the number of 1's is 0 or even.
1110 1011 0 Original #1 with row parity
1001 1101 1 Original #2 with row parity
0111 0110 Column parity
Then the result is the original data (with the row parities), followed by the column parities

Column parity

1110 1011 0 1001 1101 1 0111 0110
So grouping those in 4 bits is:
1110 1011 0100 1110 1101 1101 10

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