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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Akhil, <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>For clarification of questions it is best
that you ask your teacher, any help we could give you would be speculation on
our part not having access to your learning materials, your teacher, or the
context in which this was taught. If you have specific questions about
the theory of cryptography please let us know.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Ron<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> scal rahotguy
[mailto:scalrahotguy@gmail.com] <br>
<b><span style='font-weight:bold'>Sent:</span></b> Wednesday, May 03, 2006 1:17
PM<br>
<b><span style='font-weight:bold'>To:</span></b> Ron@usmedrec.com; <st1:PersonName
w:st="on">Cryptography Team Development List</st1:PersonName><br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Cryptography Team]
Hash function properties</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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face="Times New Roman"><span style='font-size:12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><span class=gmailquote><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>On 5/3/06, <b><span style='font-weight:bold'>Ron
Teitelbaum</span></b> <<a href="mailto:Ron@usmedrec.com">Ron@usmedrec.com</a>>
wrote:</span></font></span> <o:p></o:p></p>
<div>
<div>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Hi Scal,</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Can you give us some background of what you are doing?
Is this a school assignment? </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>yes. it is.<o:p></o:p></span></font></p>
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margin-left:4.8pt;margin-right:0in'>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>If it is then maybe you could give us an idea of what you do
understand and what you do not, so that we can help either with a discussion or
suggestions for other reference material. </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>yes. certainly for example in (b). I do not think I understood the question.
Eve knows the hash function and I also assumed she also knows the private key
of Bob. How can anybody knows once she sends a message with Bob's
signature? How can hash funtion's property help here? Can somebody throw light
here? <o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>thanks<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Akhil<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
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12.0pt'><o:p> </o:p></span></font></p>
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<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Ron Teitelbaum</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
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<p><b><font size=2 face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma;
font-weight:bold'>From:</span></font></b><font size=2 face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma'> <a
href="mailto:cryptography-bounces@lists.squeakfoundation.org" target="_blank">cryptography-bounces@lists.squeakfoundation.org</a>
[mailto:<a href="mailto:cryptography-bounces@lists.squeakfoundation.org"
target="_blank">cryptography-bounces@lists.squeakfoundation.org </a>] <b><span
style='font-weight:bold'>On Behalf Of </span></b>scal rahotguy<br>
<b><span style='font-weight:bold'>Sent:</span></b> Tuesday, May 02, 2006 11:17
PM<br>
<b><span style='font-weight:bold'>To:</span></b> <a
href="mailto:Cryptography@lists.squeakfoundation.org" target="_blank">Cryptography@lists.squeakfoundation.org</a><br>
<b><span style='font-weight:bold'>Subject:</span></b> [Cryptography Team] Hash
function properties</span></font><o:p></o:p></p>
</div>
</div>
<div><span id="q_10afa1e35f41e5f4_1">
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> <o:p></o:p></span></font></p>
<div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>For each
of the following applications of hash functions, explain which of hash
function properties (preimage resistant, second preimage resistant and
collision resistant) are needed and which are not. <br>
<br>
<br>
(a) Cryptographic signatures are produced by computing a hash of a message,
then applying a signature function to the hash of the message. Suppose Eve has
a list of messages m1,...mn, and their signatures computed using Bob's signing
key, but does not have Bob's signing key. Assuming that the signature function
is not susceptible to attack, it should not be possible for Eve to present
Bob's signature on any message other than m1,...mn. <br>
<br>
(b) Suppose that Eve works for a Certificate Authority. She does not have
access to the special harware that computes digital signatures, but she knows
the hash function. In addition, Eve can get messages signed, but every message
that is signed automatically goes into a log file that Eve cannot change. Eve
should not be able to produce a certificate signed by the Certificate Authority
that does not appear in the log file. <br>
<br>
Anybody can explain these to me?<br>
<br>
thanks<br>
Akhil<o:p></o:p></span></font></p>
</div>
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<o:p></o:p></span></font></p>
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