[ietf-dkim] Re: Rating of the Attacks and Detection

[Jim Fenton]

Hector,

Good analysis.  There are a lot of dimensions along which one could rate
the attacks, so I just had to pick one (well, two).

I had some trouble interpreting from your message whether some of the
attacks should be rated differently (according to the two parameters I
used), or not.  Do you have any specific suggestions?

-Jim

Hector Santos wrote:
> ----- Original Message -----
> From: "Jim Fenton" <fenton at cisco.com>
>
>   
>> I do recognize my role on this is as a document editor, and
>> I will adjust the document to group consensus, but I wanted you
>> to know where I was coming from.
>>     
>
> I hate going crazy on people's documents. :-) So I will minimize my
> comments to illustrating how I view the Attacks and Ratings.
>
> With my manager hat on, I read this document and ask myself a few
> questions:
>
>     "I trust the work. But what is the summary?"
>
>     1) Which attacks do I need to be concern about?
>     2) Which attacks are addressed by DKIM/SSP?
>
> In the first question, I am interested in the "worst case" scenario.  To
> do this, I can associate the ratings with a value, lets say:
>
>     High     = 10
>     M/H      = 8
>     Medium   = 5
>     Low      = 1
>
> and get a rough rating for each attack by adding impact + likelihood.
>
> When you do this, you will see the top 4 attacks are:
>
> --------------------------------------------+--------+------------+
> Attack Name                                 | Impact | Likelihood |
> --------------------------------------------+--------+------------+
> Denial-of-service attack against verifier   |  High  |   Medium   |
> Denial-of-service attack against key service|  High  |   Medium   |
> Display name abuse                          | Medium |    High    |
> Compromised system within originator's net  |  High  |   Medium   |
>
> One might suggest or ask "Is this a true relection of a high concern
> attacks?"
>
> So I will analyze this a different way as well, by measuring the
> likehihood, i.e, how often do I have worry about these attacks?
>
> o Ordered by Likelihood/Impact
>
> --------------------------------------------+--------+------------+
> Attack Name                                 | Impact | Likelihood |
> --------------------------------------------+--------+------------+
> Display name abuse                          | Medium |    High    |
> Signed message replay                       |   Low  |    High    |
> Chosen message replay                       |   Low  |     M/H    |
> Denial-of-service attack against verifier   |  High  |   Medium   |
> Denial-of-service attack against key service|  High  |   Medium   |
> Compromised system within originator's net  |  High  |   Medium   |
> Theft of delegated private key              | Medium |   Medium   |
> Body length limit abuse                     | Medium |   Medium   |
> Falsification of key service replies        | Medium |   Medium   |
> Verification probe attack                   | Medium |   Medium   |
> Canonicalization abuse                      |   Low  |   Medium   |
> Theft of private key for domain             |  High  |     Low    |
> Private key recovery via side-channel attack|  High  |     Low    |
> Compromise of key server                    |  High  |     Low    |
> Publication of bad key records and/or sigs  |  High  |     Low    |
> Cryptographic weaknesses in sigs            |  High  |     Low    |
> Use of revoked key                          | Medium |     Low    |
> --------------------------------------------+--------+------------+
>
> When viewed in this perspective, one might begin to question the level
> of impact and also ask if the attack is detectable and if a system can
> recover from such an attack.
>
> One might suggest that all theft has a high impact.
>
> One might suggest that any high occurence attack will always have a high
> impact in some form or another as well, unless there is a detection
> concept implemented in order to minimize the impact.
>
> For example, one might suggest that if the Signed/Chosen message replay
> attacks have high likelihood of occurence, then the impact is high,
> rather than low.
>
> So from a DKIM/SSP perspective, I think what might be useful, if we had
> a 3rd column, called Detection/Recovery which also rates the
> effectiveness of DKIM/SSP to detect and/or recover from the attack.
>
> I know this can be highly subjective, but we can probably use a rating
> like:
>
>   MEDIUM - Detectable using deterministic non-DKIM/SSP method
>   HIGH   - Detectable using deterministic DKIM/SSP method
>   LOW    - Not detectable until reported by human/scoring
>
> By doing it this way,  we get to see an angle for the effective of the
> DKIM/SSP protocol and how it can also be assisted by other
> recommendations as well and also which ones we really have to worry
> about.
>
> This is the rough cut at this, so it could be wrong:
>
> o LOW - Not detectable until reported by human/scoring
>
> --------------------------------------------+--------+------------+
> Attack Name                                 | Impact | Likelihood |
> --------------------------------------------+--------+------------+
> Compromised system within originator's net  |  High  |   Medium   |
> Theft of delegated private key              | Medium |   Medium   |
> Theft of private key for domain             |  High  |     Low    |
> Compromise of key server                    |  High  |     Low    |
> Cryptographic weaknesses in sigs            |  High  |     Low    |
>
> o MEDIUM - Detectable using deterministic non-DKIM/SSP method
>
> --------------------------------------------+--------+------------+
> Attack Name                                 | Impact | Likelihood |
> --------------------------------------------+--------+------------+
> Signed message replay                       |   Low  |    High    |
> Chosen message replay                       |   Low  |     M/H    |
> Denial-of-service attack against verifier   |  High  |   Medium   |
> Denial-of-service attack against key service|  High  |   Medium   |
> Falsification of key service replies        | Medium |   Medium   |
> Verification probe attack                   | Medium |   Medium   |
> Private key recovery via side-channel attack|  High  |     Low    |
>
> o HIGH - Detectable using deterministic DKIM/SSP method
>
> --------------------------------------------+--------+------------+
> Attack Name                                 | Impact | Likelihood |
> --------------------------------------------+--------+------------+
> Display name abuse                          | Medium |    High    |
> Body length limit abuse                     | Medium |   Medium   |
> Canonicalization abuse                      |   Low  |   Medium   |
> Use of revoked key                          | Medium |     Low    |
> Publication of bad key records and/or sigs  |  High  |     Low    |
>
>
> --
> Hector Santos, Santronics Software, Inc.
> http://www.santronics.com
>
>