Need this question done asap plz. Thanks! Q) If F is an error-detection function
ID: 3592349 • Letter: N
Question
Need this question done asap plz. Thanks!
Q) If F is an error-detection function, either internal or external use. If any bit of the transmitted message is altered, this will be reflected in a mismatch of the received FCS and the calculated FCS, whether the FCS function is performed inside or outside the encryption function. Some codes also provide an error-correction capability. Depending on the nature of the function, if one or a small number of bits is altered in transit, the error-correction code contains sufficient redundant information to determine the errored bit or bits and correct them. Clearly, an error-correction code will provide error correction capability when used external to the encryption function. Will it also provide this capability if used internal to the encryption function?
Explanation / Answer
The error-correction code will not provide error correction capability when used internal to the encryption function because the propagation of errors in the conversion mechanism generates a large number of errors that are difficult to correct by the error control code.
In internal error control the message M and F(M), both are encrypted [E(K,(M,F(M)))] and sent to the receiver. The receiver then decrypts the message and generates M and F(M). It then applies F on M and compares it with the received F(M).
On the other hand, in external error control first the message is encrypted and then F is applied on E(K,M).Finally E(K,M) and F(E(K,M)) are sent to the receiver. The receiver applies F on received E(K,M) and compares it with received F(E(K,M)).
Clearly we can see in internal error control errors are propagated more than in external as the receiver here(in internal) first needs to apply decryption mechanism before it can proceed further and more is the error propagation more are the number of errors generated and thus more difficult to be corrected.
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