Dean, thanks for the reply<div><br></div><div><br></div><div>Ah, I see. If I want to encrypt a 2mb file with a Symmetric Key, it just has to have a "16 byte padding" for AES, or do all the chunks need to be 16 bytes?<div>
<br></div><div>J<br><br><div class="gmail_quote">On Thu, Nov 10, 2011 at 5:17 AM, Dean Macinskas <span dir="ltr"><<a href="mailto:dmacinskas@geobridge.net">dmacinskas@geobridge.net</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
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<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D">John,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D">Unless the file is small, the typical way to encrypt a file is
to use a symmetric key, like TDES or AES. Asymmetric key crypto is
usually too slow for bulk encryption; you use a symmetric key for that, and
store/export the symmetric key using asymmetric key protection.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D">The block size of a public key is fixed by the length of the
key; in other words, if you generate a 2048 bit key, the block size is 2048
bits (256 bytes). Symmetric key block length is set by the algorithm: 8
bytes for TDES, 16 for AES. Any data you encrypt has to be padded to a
multiple of the block length.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D">If you use RSA, there are a couple of rules for encrypting data,
one of which is that the data has to be numerically less than the public modulus.
This is usually accomplished by setting the left-most bit (MSB) of the data
block to zero; another reason why using a public key directly is not a good
choice for bulk encryption.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D">HTH,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D">Dean<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D"><u></u> <u></u></span></p>
<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span style="font-size:10.0pt">From:</span></b><span style="font-size:10.0pt">
<a href="mailto:pycrypto-bounces@lists.dlitz.net" target="_blank">pycrypto-bounces@lists.dlitz.net</a> [mailto:<a href="mailto:pycrypto-bounces@lists.dlitz.net" target="_blank">pycrypto-bounces@lists.dlitz.net</a>] <b>On
Behalf Of </b>John Matthew<br>
<b>Sent:</b> Tuesday, November 08, 2011 11:59 AM<br>
<b>To:</b> <a href="mailto:pycrypto@lists.dlitz.net" target="_blank">pycrypto@lists.dlitz.net</a><br>
<b>Subject:</b> [pycrypto] Public Key encryption of files<u></u><u></u></span></p>
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<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">First off, pycrypto is awesome! Thank you for creating
it!<u></u><u></u></p>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal">I'd like to use Public Keys to encrypt files, is this
something that seems appropriate for file encryption?<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal">I've noticed that the encrypt method for RSA keys is only
256 bytes, which seems rather small.<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal">I know I could wrap that in a generator, but was hoping for
some feedback on another way or a configuration change to increase that number.<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">Thanks for your contribution, and help.<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal">J<u></u><u></u></p>
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</div>
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<br></blockquote></div><br></div></div>