Slightly OT - i need the proper wording for a signed document

vedaal at vedaal at
Thu Nov 1 20:20:33 CET 2018

Am Donnerstag, den 01.11.2018, 17:42 +0100 schrieb Stefan Claas:
> On Thu, 01 Nov 2018 16:09:56 +0100, Dirk Gottschalk wrote:


> That is the reason why i like to sign the .pdf, containing my key
> data, with a qualified eIDAS conform signature. The detached GnuPG
> sig should be an additional info, that matches the key data in the
> document. 


This will work well in that if the signature verifies, then the information in the .pdf  can be considered reliable.

It is, however, very easy for a MITM attack to 'break' the signature by very subtly altering the pdf.

Try this:

[1] Take your finished pdf and select all the text and copy it into a new Libre Office document.

[2]  At the end of your text, just add a period.

[3] Use Libre Office's font coloring to change the color of the added period to white.

[4] Export this new document as a pdf with the same file name as your original pdf, and the same metadata.

[5] The pdf looks exactly the same, but the signature will no longer verify.

I don't trust a detached, signed pdf
(Again, I do, if it verifies, but am not sure if it doesn't verify).

A simple, but slightly tedious workaround, would be to  GnuPG Armor Sign the .pdf

The elDAS signature will still work, but the Armored Signed message is much harder to alter, and such alteration is detectable as malicious rather than a 'mistake.

If you are planning to post your public keyblock in this pdf, please be aware that pdf treats a line return as empty whitespace, so when trying to import the key,
GnuPG does not recognize the empty whitespace, and reads the version line as continuous with the keyblock, and it won't import.


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