Re: [MLS] Purpose of path_secret in the Welcome message?

Théophile Wallez <theophile.wallez@inria.fr> Fri, 23 April 2021 18:17 UTC

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To: Richard Barnes <rlb@ipv.sx>
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From: =?UTF-8?Q?Th=c3=a9ophile_Wallez?= <theophile.wallez@inria.fr>
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Date: Fri, 23 Apr 2021 20:17:28 +0200
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Subject: Re: [MLS] Purpose of path_secret in the Welcome message?
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On 23/04/2021 03:24, Richard Barnes wrote:
> Ah, this might not be obvious from the spec, but the order of 
> operations for the committer and their tree is as follows:
>
> 1. Apply proposals - including adding joiners to unmerged_leaves
> 2. Generate and apply an UpdatePath
>
> In that stage 2, the nodes on the committer's direct path are 
> overwritten -- including clearing unmerged_leaves, because the 
> corresponding secret is sent to all the leaves underneath that node.  
> Continuing members get the path secret from the UpdatePath struct; new 
> members get it from GroupSecrets.path_secret.
>
> As usual, happy to clarify the spec if it can be clearer on this point.

Thank you, this clarifies the use of `path_secret`!

Indeed, I thought it was done in the reverse order (generate and apply 
an UpdatePath, then apply proposals).

Théophile.