6 \section*{Homework 6}

     6 

     7 % For Alice to cheat, she has to get her transaction into the blockchain.

     8 % For this she has to solve proof-of-work puzzles faster than anybody

     9 % else. Is it possible for her to precompute several blocks that would

    10 % validate a fraudulent transaction by her? Give a short explanation

    11 % for your reasoning.  

    12 

    13 \section*{Homework 7}

    14 

    15 \HEADER

     9 \item What are good uses of anonymity services like Tor?

    18 \item How can the hardness of the proof-of-work puzzles in

    19       Bitcoins be adjusted? What is parameter that determines

    20       how the hardness is adjusted?

    11 \item What is meant by the notion \emph{forward privacy}?

    22 \item What is the main data that is stored in Bitcoin's

    23       blockchain? 

    24       

    25 \item What is is the purpose of the proof-of-work puzzle in

    26       Bitcoins?      

    13 \item What is a \emph{re-identification attack}?

    28 \item The department has large labs full of computers that are

    29       pretty much idle over night. Why is it a bad idea to let

    30       them mine for Bitcoins?

    15 \item Imagine you have a completely `innocent' email message,

    32 \item Is it possible that Bitcoins can get lost (be

    16       like birthday wishes to your grandmother. Why should you

    33       irretrievable)?

    17       still encrypt this message and your grandmother take the

    18       effort to decrypt it? 

    20       (Hint: The answer has nothing to do with preserving the

    35 \item \POSTSCRIPT      

    21       privacy of your grandmother and nothing to do with

    36 \end{enumerate}

    22       keeping her birthday wishes supersecret. Also nothing to

    23       do with you and grandmother testing the latest

    24       encryption technology, nor just for the sake of it.)

    25 

    26 \item One part of achieving privacy (but not the only one) is to

    27   properly encrypt your conversations on the Internet.  But this is

    28   fiercely resisted by some spy agencies.  These agencies (and some

    29   politicians for that matter) argue that, for example, ISIL's

    30   recruiters broadcast messages on, say, Twitter, and get people to

    31   follow them. Then they move potential recruits to Twitter Direct

    32   Messaging to evaluate if they are a legitimate recruit. If yes, they

    33   move them to an encrypted mobile-messaging app. The spy agencies

    34   argue that although they can follow the conversations on Twitter,

    35   they ``go dark'' on the encrypted message app. To counter this

    36   ``going-dark problem'', the spy agencies push for the implementation

    37   of back-doors in iMessage and Facebook and Skype and everything else

    38   UK or US-made, which they can use eavesdrop on conversations without

    39   the conversants' knowledge or consent.\medskip

    40    

    41       What is the fallacy in the spy agencies going-dark argument?

    42       (Hint: Think what would happen if the spy agencies and certain

    43       politicians get their wish.)

    44        

    45 \item DNA data is very sensitive and can easily violate the privacy of

    46   (living) people. To get around this, two scientists from Denmark

    47   proposed to create a \emph{necrogenomic database} which would record

    48   the DNA data of all Danish citizens and residents at the time of

    49   their \emph{death}. By matching these to information about illnesses

    50   and ailments in life, helpful evidence could be gathered about the

    51   genetic origins of diseases.  The idea is that the privacy of dead

    52   people cannot be violated.

    53 

    54       What is the fallacy behind this reasoning?

    55 

    56 \item A few years ago a Google executive tried to allay worries about

    57   Google pooring over all your emails on Gmail. He said something

    58   along the lines: you are watched by an algorithm; this is like being

    59   naked in front of your dog. What is wrong with this argument?

    60 

    61 \item \POSTSCRIPT  

    62 \end{enumerate}