Security and Cost

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Security and Cost
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Security

• Means a variety of things
• Message gets through reliably
• Message doesnt get lost
• Message doesnt get garbled
• Message isnt overheard (information is one
  commodity which can be stolen in transit
  without being decreased noticeably)
• Each attempt to increase security causes a
  problem and entails a cost.

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General Communication Model
NOISE
We want the message to get through reliably with
as little loss and noise as possible. Ideally we
build barriers of noise and loss to intruders so
that they cannot enjoy our information.
Barrier
INTRU- DER
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Building Barriers-A Minimizing Message Exposure
Then again, so are the destinations!
SOURCE
EQUIVOCATION/LOSS
DESTI- NATION
PART OF ORIGINAL MESSAGE DELIVERED
By attenuating (silencing) the message, the
intruders chances of overhearing are lowered.
Barrier
INTRU- DER
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Building Barriers-B Masking the Message
However, destination has the same problem
SOURCE
DESTI- NATION
PART OF ORIGINAL MESSAGE DELIVERED
MASK
A mask makes it harder to hear the message
above the noise and raises the cost for the
intruder.
INTRU- DER
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Building Barriers-C Encoding the Message
Without a key, the destination has the same
problem
SOURCE
DESTI- NATION
Code
PART OF ORIGINAL MESSAGE DELIVERED
Encoding changes the apparent meaning of the
text, making it look like noise for the intruder
Barrier
INTRU- DER