Re: [OAUTH-WG] Pete Resnick's No Objection on draft-ietf-oauth-assertions-17: (with COMMENT)

[Brian Campbell <[e-mail]>]

Fair point. I'll add some text saying that in the next revision.

On Wed, Oct 15, 2014 at 5:18 PM, Barry Leiba <[e-mail]>
wrote:

>
>>>    Assertions used in the protocol exchanges defined by this
>>>    specification MUST always be protected against tampering using a
>>>    digital signature or a keyed message digest applied by the issuer.
>>>
>>> Why is that? Aren't you using assertions over a protected channel (as
>>> required by the spec) and therefore not need to sign the assertions?
>>> Indeed, why would a self-issued Bearer Assertion need to be signed at
>>> all? Does that even make sense?
>>>
>>>
>> Yes, assertions are sent over a protected channel, which does provide
>> integrity protection for the transport form client to AS and also gives
>> server authentication. But it doesn't provide client authentication, which
>> is kind of the point of the Client Authentication part of this draft. And
>> for authorization the signing or MACing is what authenticates the issuer of
>> the assertion - sometimes the issuer is the client but often the issuer
>> will be a 3rd party system.
>>
>> I do agree with you in one specific case that, if the client is trusted
>> to be the assertion issuer and the client is properly authenticated, then
>> an unsigned assertion could be reasonably used as an authorization grant.
>> But it's a fairly rare and very specific case. And one that can be
>> accommodated in other ways. So it's not worth introducing the complexity
>> and potential security problems that having the signature be option would
>> bring.
>>
>
> In other words, the assertion must be protected against tampering *by the
> party that presents the assertion*.  That is a significant point, and you
> should say it.
>
> Barry
>