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Virtualmin supports a flurry of algorithms for DNSSEC: RSASHA1, RSASHA256, RSAMD5, DSA, DH, HMAC-MD5(???), NSEC3RSASHA1, NSEC3DSA.

If I understand correctly, there's Proof of Concept available for SHA1 being easy to compromise when used with DKIM, because of data length. So that would lead me to believe that the same applies to DNSSEC.

Which key algorithms are most appropriate for use in DNSSEC with production environments?

And what supporting technical papers are available to substantiate the reasoning for the algorithm choice?

There's a balance to be found here however, the same one that INFOSEC so often must find, in choosing an appropriately secure algorithim without zealously draining resources in production environments.

Still, an appropriate algorithm for vital cyber systems (financial or sensitive personal information) might vary from one for mission-critical systems.

Or is the threat from man-in-the-middle attacks too great in a global cyber diaster event, such that the strongest cryptography is warranted even for mission-critical systems without highly sensitive information?

  • 1
    Well, MD5 is broken. MD5 "should be considered cryptographically broken and unsuitable for further use." So that eliminates RSAMD5 and HMAC-MD5. The IETF mailing list where DNSSEC evolved is probably a good place to ask about this, assuming the RFCs are of no help. I would guess that the security consideration sections of the DNSSEC RFCs at least touch on this. Have you looked? – Matthew Elvey May 22 '14 at 1:08
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    I don't have mathematical or cryptographical arguments (which is why this is a comment), but it might be interesting to know that >90% of deployments use RSASHA256 with the occasional RSASHA512. Key sizes tend to vary between 1024 and 4096 bits. – Habbie Jun 22 '14 at 7:51
5

(Yes, the question is old, but it deserves an answer.)

Some rules for modern crypto:

Using an HMAC for DNSSEC makes no sense, an HMAC requires both parties to have access to the same secret; in the context of DNSSEC, this means clients could spoof the server, making it useless.

There's a lot of algorithms missing from your list, I don't know why Virtualmin gives you those options. ECDSA options give you smaller responses and somewhat lower CPU usage in signing operations.

Given the relatively short lifetime of DNSSEC keys & responses, I would favor shorter options after taking all of the above in to account. This means the use of RSASHA256 with a 2048-bit RSA key or ECDSAP256SHA256 (256-bit ECDSA with SHA256).

0

As of September 2018, Viktor Dukhovni reported the algorithms observed in use and the key lengths are:

DNSKEY parameter frequency (1000 or more instances), by zone count:

 kskalgs | flags | proto | alg
 --------+-------+-------+-----
    4780 |   257 |     3 |   3
  358979 |   257 |     3 |   5
 2210428 |   257 |     3 |   7
 4198328 |   257 |     3 |   8
   87469 |   257 |     3 |  10
 1844138 |   257 |     3 |  13
   62481 |   257 |     3 |  14
 --------+-------+-------+-----

 zskalgs | flags | proto | alg
 --------+-------+-------+-----
    4780 |   256 |     3 |   3
  132748 |   256 |     3 |   5
 2192269 |   256 |     3 |   7
 4142767 |   256 |     3 |   8
   87250 |   256 |     3 |  10
  791434 |   256 |     3 |  13
   61548 |   256 |     3 |  14
 --------+-------+-------+-----

RSA key size distribution (1000 or more instances), by zone count:

 kskdomains | bits
------------+------
      67580 | 4096
    5149822 | 2048
     302182 | 1536
       2992 | 1280
    1333428 | 1024
       8392 |  512
------------+------

 zskdomains | bits
 -----------+------
      13287 | 4096
     110595 | 2048
     306770 | 1280
    6115735 | 1024
       8169 |  512
 -----------+------

The link in David's answer to the RFC will translate the alg number to the actual algorithm.

Victor posts updates of this data to the dns-operations list on a regular basis. If you are involved in DNS operations for your organization, I highly recommend subscribing to the list.

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