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Maniphest T6622

Kleopatra: Misleading result when decrypting clear signed message followed by public key block in notepad
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Description

If I put the following into notepad

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

bar
-----BEGIN PGP SIGNATURE-----

iQEzBAEBCAAdFiEE0MFuEqOl54V/b8HTD1vkKiPJHOMFAmTBMWMACgkQD1vkKiPJ
HONzdQf/aty0AjMuKRbI7s9oN2fTMzKglnopBBsJH/ozravsHt3NzW6qeI+JN8Ga
yMgwu7991di2q3+dHzLylL/uLxomh3TQnQTsak3kfzVJt8fKgY3lpFZamgpGQlme
r0xioe5ylaIipItt06XIeZMnwrS+dfDhAW1G6x98nSOCN+SlqmrPpVrf2+J3hLXq
4oRZExYD3WIQAOl5a6LBJ7nKxal7Y+ZzLNKo1Fdv0BSeaClVXTeUFCivZiw0zcEI
eguDK8fk7kx3MDuwQxV3+juWaMDCNNVV4QBIMZjXusv2i7vHkfTWrPy+m+CmkIJz
MEHj/W7d30v2HqNYtrwOSmMhv1+wOg==
=vlPl
-----END PGP SIGNATURE-----
-----BEGIN PGP PUBLIC KEY BLOCK-----
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=+jHe
-----END PGP PUBLIC KEY BLOCK-----

I get the result

Notepad → Notepad: 
Valid signature by keytocard@example.net

Signature created on Mittwoch, 26. Juli 2023 16:44:51 CEST
With certificate:
Test key for Key to Card <keytocard@example.net> (089F 4ED8 0F38 4779)
The signature is valid and the certificate's validity is ultimately trusted.

and in the text field

bar
pub   ed25519 2022-02-17 [SC] [revoked: 2022-03-28]
      81CE7D2F992F3A1EFEE05931AEEA9B17125B177B
rev        AEEA9B17125B177B 2022-03-28   [selfsig]
uid           Jane Doe <jane.doe@example.net>
sig        AEEA9B17125B177B 2022-08-09   [selfsig]
uid           blabla
sig        AEEA9B17125B177B 2022-08-09   [selfsig]
sub   cv25519 2022-02-17 [E] [revoked: 2022-03-28]
sig        AEEA9B17125B177B 2022-02-17   [keybind]

The reason seems to be that gpgme_op_verify is used on the input (because the input is classified as a clear-signed message). And this calls gpg without --verify.

Running the same input through gpg --status-fd 2, I get

[GNUPG:] PLAINTEXT 74 0 
bar
[GNUPG:] NEWSIG
[GNUPG:] KEY_CONSIDERED 8C8AFD6AEF9F30C4F6D80CF6089F4ED80F384779 0
[GNUPG:] SIG_ID rNB9tZasKqqfLCkwTNM6ht3SjzU 2023-07-26 1690382691
[GNUPG:] KEY_CONSIDERED 8C8AFD6AEF9F30C4F6D80CF6089F4ED80F384779 0
[GNUPG:] GOODSIG 0F5BE42A23C91CE3 Test key for Key to Card <keytocard@example.net>
[GNUPG:] VALIDSIG D0C16E12A3A5E7857F6FC1D30F5BE42A23C91CE3 2023-07-26 1690382691 0 4 0 1 8 01 8C8AFD6AEF9F30C4F6D80CF6089F4ED80F384779
[GNUPG:] KEY_CONSIDERED 8C8AFD6AEF9F30C4F6D80CF6089F4ED80F384779 0
[GNUPG:] TRUST_ULTIMATE 0 pgp
[GNUPG:] KEYEXPIRED 1647774000
pub   ed25519 2022-02-17 [SC] [revoked: 2022-03-28]
      81CE7D2F992F3A1EFEE05931AEEA9B17125B177B
rev        AEEA9B17125B177B 2022-03-28   [selfsig]
uid           Jane Doe <jane.doe@example.net>
sig        AEEA9B17125B177B 2022-08-09   [selfsig]
uid           blabla
sig        AEEA9B17125B177B 2022-08-09   [selfsig]
sub   cv25519 2022-02-17 [E] [revoked: 2022-03-28]
sig        AEEA9B17125B177B 2022-02-17   [keybind]

which correctly prints the signed plaintext separately from the key block. So, it's probably GpgME that needs to be fixed.

Revisions and Commits

rM GPGME
rMa9b28c79e92f core: Prevent wrong plaintext when verifying clearsigned signature

Related Objects

Event Timeline

• ikloecker triaged this task as Normal priority.Jul 28 2023, 2:30 PM
• ikloecker created this task.
• ikloecker added a subscriber: • werner.
In T6617#173396, @werner wrote:

What we have here is a clear text signature followed by a public key. If you run this with
gpg -o signedtext.txt --status-fd 2 signedtext.txt should only receive "bar" and not the key listing. If that is not the case something would be very wrong.

• ikloecker mentioned this in T6617: General error when trying to decrypt a public key block in the notepad.Jul 28 2023, 2:32 PM
• ikloecker added a comment.Jul 28 2023, 4:14 PM

Using -o signedtext.txt fixes the problem. Unfortunately, gpgme does

      err = add_arg (gpg, "--output");
      if (!err)
	err = add_arg (gpg, "-");
[...]
      if (!err)
	err = add_data (gpg, plaintext, 1, 1);

i.e. it tells gpg to write the output to stdout and then reads everything from stdout as plaintext.

• ikloecker added a commit: rMa9b28c79e92f: core: Prevent wrong plaintext when verifying clearsigned signature.Jul 28 2023, 4:15 PM
• werner added a comment.Jul 28 2023, 4:46 PM

Phew! This bug has been with us for more than 20 years unless gpg's behaviour has changed only later.

• werner raised the priority of this task from Normal to High.Jul 28 2023, 4:47 PM
• werner added projects: gpgme, Bug Report.
• ikloecker changed the task status from Open to Testing.Jul 28 2023, 4:56 PM
• ikloecker moved this task from Restricted Project Column to Restricted Project Column on the Restricted Project board.

Should be fixed.

The same problem occurred when decrypting/verifying a file containing a clear-signed message followed by a public key block, i.e. the result file written to disk contained the signed text followed by the printed public key.

• werner mentioned this in T6668: Release GPGME 1.22.0.Aug 21 2023, 9:59 AM
• herringbur added a subscriber: • herringbur.Aug 23 2023, 8:58 AM
This comment was removed by • aheinecke.
• aheinecke added a subscriber: • aheinecke.Aug 23 2023, 9:16 AM
• ebo closed this task as Resolved.Sep 28 2023, 1:52 PM
• ebo claimed this task.
• ebo moved this task from Restricted Project Column to Restricted Project Column on the Restricted Project board.
• ebo added a subscriber: • ebo.

After the fix everything after the Signature block is now silently discarded

• ebo moved this task from Backlog to done on the gpgme board.Sep 28 2023, 1:53 PM
• werner moved this task from done to gpgme 1.23.x on the gpgme board.Oct 25 2023, 10:17 AM
• werner edited projects, added gpgme (gpgme 1.23.x); removed gpgme.