Re: [Teep] OTrP Signature Security issue

On 2018-11-21 10:08, Hannes Tschofenig wrote:
> Hi Anders,
> 
> Thanks for raising this point.
> 
> I have been wondering whether a JSON encoding is the best choice for TEEP since web developers shouldn't actually be exposed to any of it.
> 
> Hence, my question to you is whether you have looked into COSE as well and whether your assessment would be different.

As far as I know (I'm not a COSE expert), COSE signatures have the same structure as JWS.  That is, they embed the signed data.
For systems depending on explicit object type identifiers like "TAInformation" in OTrP this becomes a bit of a nuisance.

I don't think the JOSE/COSE designers had anticipated this use case.  They would probably claim that OTrP is "misusing" JWS.

Since my own applications were based on the same idea as OTrP (explicit object types), I felt a need to do something about this.  After 5 years an 3 major revisions, I consider that done :-)

If you have a JCS implementation, combining it with JWS typically requires 10-20 lines of pretty trivial code.

Thanx,
Anders

> 
> Ciao
> Hannes
> 
> -----Original Message-----
> From: TEEP <teep-bounces@ietf.org> On Behalf Of Anders Rundgren
> Sent: Tuesday, November 20, 2018 9:57 PM
> To: teep@ietf.org
> Subject: [Teep] OTrP Signature Security issue
> 
> The following is a for brevity simplified version of the OTrP signature scheme.  That OTrP rather uses the JSON serialized version of JWS has no security advantages (or disadvantages) over the JWS compact notation shown here:
> {
>      "carObject":  "eyetc.eyetc.xyxetc"
> }
> 
> Since "carObject" isn't signed, you can replace it with anything else and the signature will still validate.
> 
> 
> Using detached JWS combined with JCS [1,2] you sign the entire JSON object as well as getting the "payload" in clear:
> {
>      "carObject": {
>         "brand":  "Ferrari",
>         "horsePower":  "450",
>         "weight":  "2357kg"
>      },
>      "signature": "eyetc..xyect"
> }
> 
> thanx,
> Anders
> 
> 1] https://tools.ietf.org/html/draft-rundgren-json-canonicalization-scheme-01
> 2] https://mobilepki.org/jws-jcs
> 
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