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.

Addendum: This assumes that you're doing the base64-encoding thing to allow integrity protection.  If we do canonicalization, this issue goes away.  But then we have to do canonicalization.


> 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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