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Re: Chartering work has started for a Linked Data Signature Working Group @W3C

From: Manu Sporny <msporny@digitalbazaar.com>
Date: Thu, 3 Jun 2021 11:49:20 -0400
To: semantic-web@w3.org
Message-ID: <866bfad3-54de-aebe-0918-7a2be0fe1a07@digitalbazaar.com>
Peter F. Patel-Schneider wrote:
> It appears to me that changing the data associated with the signature could
>  result in an unexpected true, as this data is not part of the graph that
> is verified.

Incorrect. The original RDF Dataset AND the signature options are both hashed
and signed. Adding/removing/modifying content in the signature options will
result in a different hash and cause the signature to fail.

> This does require that there be data in the signature that can be changed
> without affecting the verification function.  Alternatively, it might be
> possible to add an extra signature block, and still have the verification 
> succeed.

For signature sets, all signatures have to pass for the verify() call to
return true. If any signature fails, the verify() call will return false.

> These are both methods of subverting computer security that do not attack
> the core cryptographic functions but instead attack the association of the
>  signature with the payload.  But it is just as important to prevent these
>  attacks as other attacks.

Agree. These are well known attacks with well known solutions. It is true that
need more documentation on this in the specifications, but that's the job of a
WG to tease out what needs more documentation and what is best left to another
layer of abstraction.

-- manu

Manu Sporny - https://www.linkedin.com/in/manusporny/
Founder/CEO - Digital Bazaar, Inc.
blog: Veres One Decentralized Identifier Blockchain Launches
Received on Thursday, 3 June 2021 15:50:26 UTC

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