[core] draft-ietf-core-oscore-groupcomm: Question signature length
Jim Schaad <ietf@augustcellars.com> Thu, 10 January 2019 03:44 UTC
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From: Jim Schaad <ietf@augustcellars.com>
To: draft-ietf-core-oscore-groupcomm@ietf.org
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Date: Wed, 09 Jan 2019 19:44:13 -0800
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Subject: [core] draft-ietf-core-oscore-groupcomm: Question signature length
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I want to verify that you understand the following is true. It is not possible based on just the content of the message to determine where the encrypted body ends and the signature begins. To see why this is the case, if the signature algorithm in the context is EdDSA then it could be either signed with the x25519 curve or the x448 curve. The same thing is true with ECDSA signatures as the value ES256 implies that the hash used is SHA-256 but it does not require that the curve used to sign is P-256. It can be any of the curves that would be valid for this hash function. It might be nicer if there was a signature length encoded someplace so that the two values can easily be separated. Jim