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Date: Wed, 12 Mar 2014 15:37:35 -0500
Message-ID: <CAG8oi1OAYRgaMtoT8pMGNrcLomz9+dgi-7WKN285F0U4=LJSmQ@mail.gmail.com>
From: William Yager <will.yager@gmail.com>
To: Pavol Rusnak <stick@gk2.sk>
Content-Type: multipart/alternative; boundary=001a11c13c808e0d2504f46ecec7
Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] [RFC] Proposal: Base58 encoded HD Wallet
 root key with optional encryption
Precedence: list

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On Wed, Mar 12, 2014 at 3:24 PM, Pavol Rusnak <stick@gk2.sk> wrote:

> On 03/12/2014 09:10 PM, William Yager wrote:
> > implement this is to allow semi-trusted devices (like desktop PCs) to do
> > all the "heavy lifting". The way the spec is defined, it is easy to have
> a
> > more powerful device do all the tough key stretching work without
> > significantly compromising the security of the wallet.
>
> By disclosing "preH" to compromised computer (between steps 4 and 5) you
> make further steps 5-9 quite less important.
>
>
Yes, that was my chief complaint as well. A compromised computer removes
most of the extra security offered by key stretching (should you choose to
outsource the bulk of your key stretching).

However, I think we have a good compromise, which is the inclusion of a
number of PBKDF2-HMAC-SHA512 based KDFs. For anyone who doesn't want to
trust any external device, but also wants to use memory-contrained devices
(that group of people includes me), PBKDF2-HMAC-SHA512 is very easy to
implement even on devices that only have a few kB of RAM, and even though
our number of rounds is very aggressive (2^16 and 2^21), it will still run
in reasonable time even on very slow embedded ARM processors.

Will

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<div dir=3D"ltr">On Wed, Mar 12, 2014 at 3:24 PM, Pavol Rusnak <span dir=3D=
"ltr">&lt;<a href=3D"mailto:stick@gk2.sk" target=3D"_blank">stick@gk2.sk</a=
>&gt;</span> wrote:<br><div class=3D"gmail_extra"><div class=3D"gmail_quote=
"><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:=
1px #ccc solid;padding-left:1ex">
<div class=3D"">On 03/12/2014 09:10 PM, William Yager wrote:<br>
&gt; implement this is to allow semi-trusted devices (like desktop PCs) to =
do<br>
&gt; all the &quot;heavy lifting&quot;. The way the spec is defined, it is =
easy to have a<br>
&gt; more powerful device do all the tough key stretching work without<br>
&gt; significantly compromising the security of the wallet.<br>
<br>
</div>By disclosing &quot;preH&quot; to compromised computer (between steps=
 4 and 5) you<br>
make further steps 5-9 quite less important.<br><br>
<div class=3D"HOEnZb"><div class=3D"h5"><span style=3D"color:rgb(34,34,34)"=
></span></div></div></blockquote><div><br></div><div>Yes, that was my chief=
 complaint as well. A compromised computer removes most of the extra securi=
ty offered by key stretching (should you choose to outsource the bulk of yo=
ur key stretching).</div>
<div><br></div><div>However, I think we have a good compromise, which is th=
e inclusion of a number of PBKDF2-HMAC-SHA512 based KDFs. For anyone who do=
esn&#39;t want to trust any external device, but also wants to use memory-c=
ontrained devices (that group of people includes me), PBKDF2-HMAC-SHA512 is=
 very easy to implement even on devices that only have a few kB of RAM, and=
 even though our number of rounds is very aggressive (2^16 and 2^21), it wi=
ll still run in reasonable time even on very slow embedded ARM processors.<=
/div>
<div><br></div><div>Will</div></div><br></div></div>

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