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Re: [openpgp] Backwards compatibility vs streaming verification of v6 clearsigned messages

Daniel Kahn Gillmor <dkg@fifthhorseman.net> Wed, 24 May 2023 20:42 UTC

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From: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
To: Andrew Gallagher <andrewg=40andrewg.com@dmarc.ietf.org>
Cc: IETF OpenPGP WG <openpgp@ietf.org>
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Autocrypt: addr=dkg@fifthhorseman.net; prefer-encrypt=mutual; keydata= mDMEX+i03xYJKwYBBAHaRw8BAQdACA4xvL/xI5dHedcnkfViyq84doe8zFRid9jW7CC9XBiI0QQf FgoAgwWCX+i03wWJBZ+mAAMLCQcJEOCS6zpcoQ26RxQAAAAAAB4AIHNhbHRAbm90YXRpb25zLnNl cXVvaWEtcGdwLm9yZ/tr8E9NA10HvcAVlSxnox6z62KXCInWjZaiBIlgX6O5AxUKCAKbAQIeARYh BMKfigwB81402BaqXOCS6zpcoQ26AADZHQD/Zx9nc3N2kj13AUsKMr/7zekBtgfSIGB3hRCU74Su G44A/34Yp6IAkndewLxb1WdRSokycnaCVyrk0nb4imeAYyoPtBc8ZGtnQGZpZnRoaG9yc2VtYW4u bmV0PojRBBMWCgCDBYJf6LTfBYkFn6YAAwsJBwkQ4JLrOlyhDbpHFAAAAAAAHgAgc2FsdEBub3Rh dGlvbnMuc2VxdW9pYS1wZ3Aub3JnL0Gwxvypz2tu1IPG+yu1zPjkiZwpscsitwrVvzN3bbADFQoI ApsBAh4BFiEEwp+KDAHzXjTYFqpc4JLrOlyhDboAAPkXAP0Z29z7jW+YzLzPTQML4EQLMbkHOfU4 +s+ki81Czt0WqgD/SJ8RyrqDCtEP8+E4ZSR01ysKqh+MUAsTaJlzZjehiQ24MwRf6LTfFgkrBgEE AdpHDwEBB0DkKHOW2kmqfAK461+acQ49gc2Z6VoXMChRqobGP0ubb4kBiAQYFgoBOgWCX+i03wWJ BZ+mAAkQ4JLrOlyhDbpHFAAAAAAAHgAgc2FsdEBub3RhdGlvbnMuc2VxdW9pYS1wZ3Aub3Jnfvo+ nHoxDwaLaJD8XZuXiaqBNZtIGXIypF1udBBRoc0CmwICHgG+oAQZFgoAbwWCX+i03wkQPp1xc3He VlxHFAAAAAAAHgAgc2FsdEBub3RhdGlvbnMuc2VxdW9pYS1wZ3Aub3JnaheiqE7Pfi3Atb3GGTw+ jFcBGOaobgzEJrhEuFpXREEWIQQttUkcnfDcj0MoY88+nXFzcd5WXAAAvrsBAIJ5sBg8Udocv25N stN/zWOiYpnjjvOjVMLH4fV3pWE1AP9T6hzHz7hRnAA8d01vqoxOlQ3O6cb/kFYAjqx3oMXSBhYh BMKfigwB81402BaqXOCS6zpcoQ26AADX7gD/b83VObe14xrNP8xcltRrBZF5OE1rQSPkMNy+eWpk eCwA/1hxiS8ZxL5/elNjXiWuHXEvUGnRoVj745Vl48sZPVYMuDgEX+i03xIKKwYBBAGXVQEFAQEH QIGex1WZbH6xhUBve5mblScGYU+Y8QJOomXH+rr5tMsMAwEICYjJBBgWCgB7BYJf6LTfBYkFn6YA CRDgkus6XKENukcUAAAAAAAeACBzYWx0QG5vdGF0aW9ucy5zZXF1b2lhLXBncC5vcmcEAx9vTD3b J0SXkhvcRcCr6uIDJwic3KFKxkH1m4QW0QKbDAIeARYhBMKfigwB81402BaqXOCS6zpcoQ26AAAX mwD8CWmukxwskU82RZLMk5fm1wCgMB5z8dA50KLw3rgsCykBAKg1w/Y7XpBS3SlXEegIg1K1e6dR fRxL7Z37WZXoH8AH
Date: Wed, 24 May 2023 15:08:22 -0400
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Subject: Re: [openpgp] Backwards compatibility vs streaming verification of v6 clearsigned messages
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On Wed 2023-05-24 14:14:11 +0100, Andrew Gallagher wrote:
> On 19 May 2023, at 15:42, Daniel Huigens <d.huigens=40protonmail.com@dmarc.ietf.org> wrote:
>> 
>> In OpenPGP.js and GopenPGP, cleartext signed messages with header names
>> other than "Hash" are rejected. The reason is to prevent messages like:
>> 
>>    -----BEGIN PGP SIGNED MESSAGE-----
>>    Reminder: I need you to wire $100k to 12345566 as soon as possible.
>> 
>>    Thank you!
>>    -----BEGIN PGP SIGNATURE-----
>>    [...]
>> 
>> from being able to trick a user into thinking the entire message was
>> signed.
>
> The most general (and compatible) solution would be to require that these headers are never displayed to the user.

the thing about the cleartext signing framework is that it's designed
(and i think intended) to work on data that will be viewed directly by a
human in a program that knows nothing about OpenPGP.

So "requiring that these headers are never displayed to the user" isn't
really a possibility -- the rendering/display programs for the
underlying data doesn't even need to know that the content is OpenPGP,
so we can't impose any effective restrictions on viewer behavior.

           --dkg

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