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Re: [webauthn] Floating-point values in the CTAP2 canonical CBOR encoding form (#1263)

From: Peter Occil via GitHub <sysbot+gh@w3.org>
Date: Fri, 26 Jul 2019 07:10:25 +0000
To: public-webauthn@w3.org
Message-ID: <issue_comment.created-515337246-1564125023-sysbot+gh@w3.org>
I see that currently, of the WebAuthn extensions, only the location extension uses floating-point values, namely `double`s encoded with the CBOR 64-bit encoding.  However, I didn't check whether any current attestations use floating-point values, or whether any other known user of the CTAP canonical CBOR encoding form uses floating-point values.

The issue I raised is important especially because the [draft revision of CBOR](https://tools.ietf.org/html/draft-ietf-cbor-7049bis-06#section-2) defines a data model that includes binary64 floating-point values regardless of how they were encoded in a CBOR document (whether with the 64-, 32-, or 16-bit encoding).  To encourage reuse of code implementing the CTAP canonical form, the matter of how to encode floating-point numbers should be left to the CTAP canonical form rather than delegated to extensions, attestations, etc., that may use such floating-point numbers.  Since only the location extension uses such numbers at the moment, that may be as simple as saying that "all floating-point values are encoded as 64-bit CBOR floating-point numbers" in the CTAP canonical form.

GitHub Notification of comment by peteroupc
Please view or discuss this issue at https://github.com/w3c/webauthn/issues/1263#issuecomment-515337246 using your GitHub account
Received on Friday, 26 July 2019 07:10:26 UTC

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