Re: [jose] New Version Notification for draft-barnes-jose-jsms-00.txt

["Richard L. Barnes" <[e-mail]>]

Sure, multiple signature is easier than multiple recipients.  But I wouldn't call it simple.  I have to base64url-decode each header to figure out which one to use (but keep around the encoded version, so I can verify the signature), keep track of the corresponding signature value, and reconstruct the signed body -- all before I can do the actual signature verification.

OTOH, without integrity-protection, you can just have the signature beside all the other parameters, in plain JSON, so that you can just grab stuff and go.

From <https://raw.github.com/bifurcation/jsms/master/jose.js>:

    verify: function(object) {
        var jsms = JSON.parse(object);
        if (!_JOSE_Support.isSignedData(jsms)) {
            throw "Invalid SignedData object";
        }

        // Figure out which signatures are valid
        var validPublicKeys = [];
        var sigs = jsms.signatures;
        for (var i=0; i<sigs.length; ++i) {
            var result = _JOSE_Crypto.verify_pkcs1_sha256(
                sigs[i].key.n, sigs[i].key.e, jsms.content, sigs[i].signature)
            if (result = "True") {
                validPublicKeys.push(sigs[i].key);
            }
        }

        return validPublicKeys;
    }




On Jun 26, 2012, at 6:03 PM, Mike Jones wrote:

> http://tools.ietf.org/html/draft-jones-json-web-signature-json-serialization-01 is an existence proof that it's not hard to sign the parameters and have multiple signatures.
> 
> 				-- Mike
> 
> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]] On Behalf Of Richard L. Barnes
> Sent: Tuesday, June 26, 2012 10:46 AM
> To: Brian Campbell
> Cc: John Bradley; [e-mail]
> Subject: Re: [jose] New Version Notification for draft-barnes-jose-jsms-00.txt
> 
> I agree with that goal!  I disagree that JWS is a good solution.  
> 
> It is true that JWS provides a relatively simple mechanism for a single signature, but:
> 1. It could be simpler (see below)
> 2. JWS header protection is useless for the single-signature case, and makes the multiple-signature/recipient case harder
> 
> --Richard
> 
> 
> 
> On Jun 26, 2012, at 12:16 PM, Brian Campbell wrote:
> 
>> I wasn't suggesting that integrity-protecting the header itself makes 
>> things simpler. Rather that a desirable goal is for support of a 
>> relatively simple model utilizing a single signature over the whole 
>> message. And that we already have that in JWS.
>> 
>> On Mon, Jun 25, 2012 at 3:55 PM, Richard L. Barnes <[e-mail]> wrote:
>>> 
>>> On Jun 25, 2012, at 5:53 PM, Richard L. Barnes wrote:
>>> 
>>>>>> I think part of this is that as one of the openID Connect authors I look at this as a necessary security token format, for OAuth and Connect.
>>>>>> For that simple processing with one signature is a high priority for adoption.
>>>>> 
>>>>> +1.
>>>>> 
>>>>> A simple JSON friendly model supporting a single signature over the 
>>>>> entire message (including headers) is an important case for 
>>>>> adoption (and security). JWS provides that now and there are 
>>>>> already numerous interoperable JWS implementations available or in the works.
>>>> 
>>>> I'm not sure how people think that integrity-protecting the header makes things *simpler*, especially since it adds a whole new decoding step and makes the parsing more complicated.
>>>> 
>>>> Pseudocode without integrity protection (assuming JSMS format, but JWS could be made to look similar):
>>>> function verify(json) {
>>>>   jose = JSON.parse(json);
>>>>   // Check algorithm values
>>>>   return Crypto.SignatureAlgorithm.verify(jose.content, 
>>>> jose.keys[0].signature, jose.keys[0].key); }
>>>> 
>>>> Pseudocode with integrity protection (assuming JWS format):
>>>> function verify(jws) {
>>>>   (txtHeader, content, signature) = jws.split("\.");
>>>>   protectedBody = header + "." + content
>>>>   jsonHeader = base64url.decode(txtHeader);
>>>>   header = JSON.parse(jsonHeader);
>>>>   return Crypto.SignatureAlgorithm.verify(content, signature, 
>>>> header.jwk); }
>>>> 
>>> 
>>> Err, sorry, that should read:
>>>   protectedBody = txtHeader + "." + content; and
>>>   return Crypto.SignatureAlgorithm.verify(protectedBody, signature, 
>>> header.jwk);
>>> 
>>> See how hard it is to get right?  :)
>>> 
>>> --Richard
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