Re: [Acme] Hash algorithms for challenges

I would rather see new challenges defined with a new hash function
than introduce orthogonal hash negotiation.

On 8 March 2017 at 09:40, Logan Widick <logan.widick@gmail.com> wrote:
> I noticed that the challenges in the draft seem to be tied to the same
> hash algorithm (SHA-256). Would it be possible to have the the server
> include an array of supported hash algorithms, and then have the
> client specify which one of the server's supported algorithms is used
> in the response? This way, the hash algorithms can be changed when
> needed without changing the challenges themselves.
>
> For example, consider the following directory, modified to include the
> server's supported hash algorithms:
> {
>   "new-nonce": "https://example.com/acme/new-nonce",
>   //other standard URIs here
>   "meta": {
>     "terms-of-service": "https://example.com/acme/terms",
>     "website": "https://www.example.com/",
>     "caa-identities": ["example.com"],
>     "hash-algorithms": ["SHA-256", "SHA-512"]
> },
>
> Alternatively, the server's hash algorithms could be included in the
> challenges, like this:
> {
>    "type": "http-01",
>    "url": "https://example.com/authz/1234/0",
>    "token": "DGyRejmCefe7v4NfDGDKfA",
>    "hash-algorithms":["SHA-256", "SHA-512"]
> }
>
> Then, the client indicates the preferred hash algorithm (from the
> server's list) in the response:
> {
>   "protected": base64url({
>     "alg": "ES256",
>     "kid": "https://example.com/acme/acct/1",
>     "nonce": "Q_s3MWoqT05TrdkM2MTDcw",
>     "url": "https://example.com/acme/authz/asdf/0"
>   }),
>   "payload": base64url({
>     "type": "http-01",
>     "keyAuthorization": "IlirfxKKXA...vb29HhjjLPSggwiE",
>     "hash-algorithm": "SHA-256"
>   }),
>   "signature": "9cbg5JO1Gf5YLjjz...SpkUfcdPai9uVYYQ"
> }
>
> For compatibility with existing implementations, the default hash
> algorithm if none is specified could be SHA-256.
>
> Sincerely,
>
> Logan Widick
>
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