Re: [DNSOP] Current DNSOP thread and why 1024 bits

S Moonesamy <sm+ietf@elandsys.com> Wed, 02 April 2014 16:13 UTC

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Date: Wed, 02 Apr 2014 09:06:32 -0700
To: Edward Lewis <edlewis.subscriber@cox.net>, dnsop@ietf.org
From: S Moonesamy <sm+ietf@elandsys.com>
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Subject: Re: [DNSOP] Current DNSOP thread and why 1024 bits
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Hi Ed,
At 06:30 02-04-2014, Edward Lewis wrote:
>I found that there are two primary reasons why 1024 bits is used in 
>zone signing keys.
>
>  One - peer pressure.  Most other operators start out with 1024 
> bits.  I know of some cases where operators wanted to choose other 
> sizes but were told to "follow the flock."
>
>Two - it works.  No one has ever demonstrated a failure of a 1024 
>bit key to provide as-expected protection.

My short comment would be Yes to the above.

The problem might be the "follow the flock" as there is an assumption 
that someone looked at the details before choosing the 1024 bit key.

>What does it matter from a security perspective?  DNS messages are 
>short lived.  It's not like we are encrypting a novel to be kept 
>secret for 100 years.  With zone signing keys lasting a month, 6 
>months, or so, and the ability to disallow them fairly quickly, 
>what's the difference between this so-called 80 or 112 bit strength 
>difference?  Yes, I understand the doomsday scenario that someone 
>might "guess" my private key and forge messages.  But an attack is 
>not as simple as forging messages, it takes the ability to inject 
>them too.  That can be done - but chaining all these things together 
>just makes the attack that much less prevalent.

For context, the discussion is about a ZSK.  There is a theory that 
it would take under a year and several million (U.S.) dollars to 
break 1024 bits.  It has been said (not on this mailing list) that an 
organization could do it within a shorter time.  It's not a good idea 
to wait for the demonstration as it can raise concerns about the 
entity which chose the key.

As a general comment I tried to find out which NIST recommendations 
are being discussed in respect to DNSSEC.  The requirements mentioned 
by Joe Abley refers to NIST SP 800-78.  That document is about 
"Cryptographic Algorithms and Key Sizes for Personal Identity
Verification".  Is that the NIST recommendation on which this 
discussion is based?

Regards,
S. Moonesamy