Re: Outstanding question - rule on cleartext signing last line

[Ben Laurie <[e-mail]>]

David Shaw wrote:
> On Mon, Dec 26, 2005 at 04:20:28PM +0000, Ian G wrote:
>> David Shaw wrote:
>>
>>> Can you give an example of why you feel this is a bug?
>> I think it is a bug if we decide that the
>> process of cleartext signing is reversable.
> 
> Can you please give an example of how the current system is not
> reversible?
> 
> As far as I can see, the current system is quite reversible.  For
> example, given a document reading "this is a test" (no line ending,
> and the last character in the file is the second t from test), here's
> a clear signature:
> 
> test  <<-----  There is a CRLF here, but it is NOT PART OF THE SIG

> Now given a document reading "this is a test<LINEENDING>", here's a
> clear signature:

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

test  <<----- There is a CRLF here and it IS PART OF THE SIG
<<-----  There is a CRLF here, but it is NOT PART OF THE SIG
-----BEGIN PGP SIGNATURE-----

blah blah blah
-----END PGP SIGNATURE-----

> In what way is this not reversible?

>> So, if the process of verification creates
>> a file that is the pre-signed version, then
>> it has to decide whether the final CRLF has
>> to be preserved or stripped in the unsigned
>> output.

> The final CRLF is not part of the document.  If a user/implementation
> wants a final CRLF in there that is part of the document, they need to
> add one.

> Think of the "BEGIN PGP SIGNATURE" string as actually being
> "CRLF-----BEGIN PGP SIGNATURE".  It's part of the message structure
> and not part of the signed text.

If that were what happened, I'd be happy. But it isn't.

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