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<div class="moz-cite-prefix">On 12/12/2012 07:58 PM, Ian Goldberg
wrote:<br>
</div>
<blockquote cite="mid:20121212185841.GQ14026@thunk.cs.uwaterloo.ca"
type="cite">
<pre wrap="">On Wed, Dec 12, 2012 at 07:51:38PM +0100, . wrote:
</pre>
<blockquote type="cite">
<pre wrap="">On 12/12/2012 05:06 PM, Ian Goldberg wrote:
</pre>
<blockquote type="cite">
<pre wrap="">On Wed, Dec 12, 2012 at 02:48:51PM +0100, . wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Off-The-Record (OTR) encryption uses DSA 1024bit (DSA goes up to only
1024bit, equals ~1320bit RSA) and is not secure for the next 10years or
so, or do you want your messages to be readable/encryptable within your
lifetime?
</pre>
</blockquote>
<pre wrap="">DSA isn't used for encryption at all, but only for authentication. If
an OTR conversation uses DSA-1024 today, and DSA-1024 is broken next
year, today's conversation remains secure. The authentication crypto
only has to be secure *at the time of the conversation*.
The encryption used by OTR is DH-1536 and AES-128, both of which are
believed to be fine for a while.
- Ian
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</pre>
</blockquote>
<pre wrap="">
DH-1536 is RSA-1536 I guess (for exchanging the AES key, and use AES
then for speed reasons).
</pre>
</blockquote>
<pre wrap="">
No, RSA is not used at all in OTR.</pre>
</blockquote>
DH is Diffie–Hellman, right? I thought it uses RSA to exchange the
symmetric keys.<br>
Just read:<br>
<blockquote>Therefore, both DH and RSA recommended key sizes are the
same.<br>
</blockquote>
<blockquote cite="mid:20121212185841.GQ14026@thunk.cs.uwaterloo.ca"
type="cite">
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">But isn't the traffic captured anyway and if one can encrypt RSA-1536
and see the AES key, then the security is broken. Why not use
RSA-4096? Is it because of the computation time? Why is it not
possible to choose RSA-4096 in the pidgin-otr plugin?
</pre>
</blockquote>
<pre wrap="">
What's the advantage of RSA-4096 over RSA-1536? Are you really worried
that RSA-1536 will be easy to break soon? Remember also that it doesn't
make sense to make one piece of the crypto much stronger than other
pieces. So RSA-4096 (if OTR were to use RSA) would be quite mismatched
to AES-128 and SHA-256.</pre>
</blockquote>
1536bit is really not too much, even twitter uses 2048bit, facebook
& co will update to 2048 soon too.<br>
You know encryption should last a lifetime.<br>
Can I change the 1536 to higher values in the source code (looking
at the char* names I guess no)?<br>
libotr-4.0.0$ grep -r "1536" .<br>
dh.c:static const int DH1536_MOD_LEN_BITS = 1536;<br>
<blockquote cite="mid:20121212185841.GQ14026@thunk.cs.uwaterloo.ca"
type="cite">
<pre wrap="">
Why it's not possible to choose the crypto to use: that would cause
incompatibilities. If everyone could choose their own crypto, then some
people wouldn't be able to talk to other people, and there would
possibly even be rollback attacks where an adversary could trick you
into using a weaker cipher than you expect, by claiming not to support
strong ones.</pre>
</blockquote>
Claiming that one can only use 2048bit instead of 4096bit should not
be possible by the program :)<br>
Using 4096bit should at least be possible by doing ./configure
--dh4096 and it should be fixed and not claimable.<br>
I'd -- and others I guess -- even be happy (for the next 5years (in
reality 2048bit would last longer but it's about not be able to
decrypt something for a lifetime)) with 2048 ~AES-112, not AES-128,
and it's still fast to create a key. <br>
Please switch to 2048 <br>
<blockquote cite="mid:20121212185841.GQ14026@thunk.cs.uwaterloo.ca"
type="cite">
<pre wrap="">
- Ian
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</pre>
</blockquote>
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