Suppose N people want to communicate with each of N-1 other people using symmetric key encryption. All communication between any two people, i and j, is visible to all other people in this group of N, and no other person in this group should be able to decode their communication. How many keys are needed in the system as a whole? For a sample scenario for this problem, if there are N=3 people, Bob, Alice, Trudy, then one symmetric key is shared by each pair: Bob-Alice, Alice-Trudy, Bob-Trudy, giving a total count of keys= 3. You need to give the general expression for N nodes, which must clearly also satisfy this example.

My favorite is "be concise."have you ever received an email and had to read a page full of information? by the time you finished reading it, you had to re-read it? i have even hit "reply" so that i could break it down into separate paragraphs and send it back to myself.what is concise? get to the point, fast. when opening an email like this, some will close it or print it to read later.i learned to use the subject line to prepare the reader for content. such as, "need on (blank), " "info only re: (blank)," "request input on (blank)," "read before (blank) meeting." these are just some.if you are asking for something, make that your first sentence. follow this by who, what, when, where, and how. use these, as necessary. example; (1) who (who needs it and or who does it), (2) what (specific description of what is needed), (3) when (specific, i need this by 8: 00 am monday or i need this by 10: 00 am today), (4) where (does it have to be printed and taken to someone, maybe the place of the meeting), (5) how (i need it scanned or faxed back to me at this email address, provide me with a hard copy).do not send yet. re-read it. did some spell check change a word? maybe let someone else read it for understanding. you want to avoid multiple emails asking for clarification. if important, put a read receipt on it. you will know it was opened, not necessarily read.end with a you.

When setting up a domain controller in a remote branch office

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By default, powerpoint opens in normal view, displaying the thumbnails, notes and slide view. if you prefer, however, you can specify that powerpoint open in a different view, such as slide sorter view, slide show view, notes page view, and variations on normal view.