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gpg: Make the use of "--verify FILE" for detached sigs harder.

Browse source 
* g10/openfile.c (open_sigfile): Factor some code out to ...
(get_matching_datafile): new function.
* g10/plaintext.c (hash_datafiles): Do not try to find matching file
in batch mode.
* g10/mainproc.c (check_sig_and_print): Print a warning if a possibly
matching data file is not used by a standard signatures.
--

Allowing to use the abbreviated form for detached signatures is a long
standing bug which has only been noticed by the public with the
release of 2.1.0.  :-(

What we do is to remove the ability to check detached signature in
--batch using the one file abbreviated mode.  This should exhibit
problems in scripts which use this insecure practice.  We also print a
warning if a matching data file exists but was not considered because
the detached signature was actually a standard signature:

  gpgv: Good signature from "Werner Koch (dist sig)"
  gpgv: WARNING: not a detached signature; \
  file 'gnupg-2.1.0.tar.bz2' was NOT verified!

We can only print a warning because it is possible that a standard
signature is indeed to be verified but by coincidence a file with a
matching name is stored alongside the standard signature.

Reported-by: Simon Nicolussi (to gnupg-users on Nov 7)
Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch 2014-11-13 17:39:31 +01:00
parent 22748338da
commit 69384568f6
5 changed files with 125 additions and 51 deletions
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26
doc/gpg.texi
View file

@ -214,16 +214,22 @@ files which don't begin with an encrypted message.
@item --verify
@opindex verify
Assume that the first argument is a signed file or a detached signature
and verify it without generating any output. With no arguments, the
signature packet is read from STDIN. If only a sigfile is given, it may
be a complete signature or a detached signature, in which case the
signed stuff is expected in a file without the ".sig" or ".asc"
extension. With more than 1 argument, the first should be a detached
signature and the remaining files are the signed stuff. To read the
signed stuff from STDIN, use @samp{-} as the second filename. For
security reasons a detached signature cannot read the signed material
from STDIN without denoting it in the above way.
Assume that the first argument is a signed file and verify it without
generating any output. With no arguments, the signature packet is
read from STDIN. If only a one argument is given, it is expected to
be a complete signature.
With more than 1 argument, the first should be a detached signature
and the remaining files ake up the the signed data. To read the signed
data from STDIN, use @samp{-} as the second filename. For security
reasons a detached signature cannot read the signed material from
STDIN without denoting it in the above way.
Note: If the option @option{--batch} is not used, @command{@gpgname}
may assume that a single argument is a file with a detached signature
and it will try to find a matching data file by stripping certain
suffixes. Using this historical feature to verify a detached
signature is strongly discouraged; always specify the data file too.
Note: When verifying a cleartext signature, @command{gpg} verifies
only what makes up the cleartext signed data and not any extra data