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#1
September 28th, 2011, 06:22 PM
 Smoothe19
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Non-digital watermarking/Key diversification

First of all it is not HW.. I am self-teaching myself cryptography but have troubles with these two concepts:

- Suppose that you have a text file and you plan to distribute it to several different people. Describe a simple non-digital watermarking method that you could use to place a distinct invisible watermark in each copy of the file. Note that in this context, “invisible” does not imply that the watermark is literally invisible—instead, it means that the watermark is not obvious to the reader

- Suppose that Sally (a server) needs access to a symmetric key for user Alice andanother symmetric key for Bob and another symmetric key for Charlie. Then Sallycould generate symmetric keys KA,KB, and KC and store these in a database. An alternative is key diversi?cation, where Sally generates and stores a singlekey KS . Then Sally generates the key KA when required as KA = h(Alice,KS ),with keys KB and KC generated in a similar manner. Describe one advantage andone disadvantage of key diversification

#2
September 29th, 2011, 10:26 PM
 OmegaZero
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Quote:
 Originally Posted by Smoothe19 First of all it is not HW.. I am self-teaching myself cryptography but have troubles with these two concepts:

Regardless of if it actually is homework or not, people on these forums avoid questions that look like someone just dumped their work into a forum post. To get better (or any) answers, show what you've done so far, and ask specific questions about what you don't understand.

Quote:
 Originally Posted by Smoothe19 Suppose that you have a text file and you plan to distribute it to several different people...

What are some different ways to format the same text? Is there anything in a text file not visible to a reader? In a plain text file, how is "justified text" (text flush with both the left and right margins) produced?

Quote:
 Originally Posted by Smoothe19 Suppose that Sally (a server) needs access to a symmetric key for user Alice andanother symmetric key for Bob and another symmetric key for Charlie....

What resources/operations are involved for each person in each scenario? What options are available to an attacker? What impact does a security breach have in each scenario? How is the key management going to operate in each case?
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