Re: [zcap-spec] Request for Clarification (Is it "what" or "why?" and cross-matching)

On Sun, Mar 5, 2023 at 6:37 PM Bob Wyman <bob@wyman.us> wrote:

> A capability system would do this differently.  Bob would present his
>> credentials, such as age and gender, and get back a capability authorizing
>> search with caveats limiting what he can find.  The return values would
>> include a capability to read Alice's profile.  Notice the difference?  Any
>> authorization is done up front in order to get a capability.  That
>> capability is then used to make a request.
>
> I think I now understand. Instead of including proofs with a request to
> "use Alice's 'read profile capability," Bob would provide his credentials
> as part of a request for a "read profile capability" for Alice's profile.
> Proofs are presented when requesting a capability, not when using one. Is
> that correct?
>

Correct.

But, that leaves me confused about Manu's statement:
>
>> (READ, "
>> https://docs.google.com/presentation/d/vYm4GDBZARndSKu-pMBC4RZTp5_WkAewggLo1623vnHd/edit
>> ",
>> did:key:z6MkqvajY2zUw866mQyY2LRwdPXKov1Q48Hw8RWxnKd1AeEt)
>> And whomever can do a digital signature as that did:key will learn the
>> secret of life.
>>
>> *That's a capability that requires cryptographic proofof some kind when
>> access to the document is requested. The requirementof a cryptographic
>> proof is called a "caveat"* -- that is, "You can
>> access X, as long as you meet requirements Y."
>
>
> Is this saying that the cryptographic proof is required when the
> capability is used, or that a new capability will be issued if the
> cryptographic proof is provided?
>

Manu was referring to a certificate capability system.  The certificate is
created with a public key, did:key in this case.  You must prove knowledge
of the corresponding private key to use the certificate as a capability.

--------------
Alan Karp


On Sun, Mar 5, 2023 at 6:37 PM Bob Wyman <bob@wyman.us> wrote:

> A capability system would do this differently.  Bob would present his
>> credentials, such as age and gender, and get back a capability authorizing
>> search with caveats limiting what he can find.  The return values would
>> include a capability to read Alice's profile.  Notice the difference?  Any
>> authorization is done up front in order to get a capability.  That
>> capability is then used to make a request.
>
> I think I now understand. Instead of including proofs with a request to
> "use Alice's 'read profile capability," Bob would provide his credentials
> as part of a request for a "read profile capability" for Alice's profile.
> Proofs are presented when requesting a capability, not when using one. Is
> that correct?
>
> But, that leaves me confused about Manu's statement:
>
>> (READ, "
>> https://docs.google.com/presentation/d/vYm4GDBZARndSKu-pMBC4RZTp5_WkAewggLo1623vnHd/edit
>> ",
>> did:key:z6MkqvajY2zUw866mQyY2LRwdPXKov1Q48Hw8RWxnKd1AeEt)
>> And whomever can do a digital signature as that did:key will learn the
>> secret of life.
>>
>> *That's a capability that requires cryptographic proofof some kind when
>> access to the document is requested. The requirementof a cryptographic
>> proof is called a "caveat"* -- that is, "You can
>> access X, as long as you meet requirements Y."
>
>
> Is this saying that the cryptographic proof is required when the
> capability is used, or that a new capability will be issued if the
> cryptographic proof is provided?
>
> bob wyman
>
>