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gnupg/doc/gpgv.texi

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@c Copyright (C) 2004 Free Software Foundation, Inc.
@c This is part of the GnuPG manual.
@c For copying conditions, see the file GnuPG.texi.
@c
@c This is included by tools.texi.
@c
@c Begin GnuPG 1.x specific stuff
@ifset gpgone
@macro gpgvname
gpgv
@end macro
@manpage gpgv.1
@node gpgv
@section Verify OpenPGP signatures
@ifset manverb
.B gpgv
\- Verify OpenPGP signatures
@end ifset
@mansect synopsis
@ifset manverb
.B gpgv
.RI [ options ]
.I signed_files
@end ifset
@end ifset
@c End GnuPG 1.x specific stuff
@c Begin GnuPG 2 specific stuff
@ifclear gpgone
@macro gpgvname
gpgv2
@end macro
@manpage gpgv2.1
@node gpgv
@section Verify OpenPGP signatures
@ifset manverb
.B gpgv2
\- Verify OpenPGP signatures
@end ifset
@mansect synopsis
@ifset manverb
.B gpgv2
.RI [ options ]
.I signed_files
@end ifset
@end ifclear
@c End GnuPG 2 specific stuff
@mansect description
@code{@gpgvname} is an OpenPGP signature verification tool.
This program is actually a stripped-down version of @code{gpg} which is
only able to check signatures. It is somewhat smaller than the fully-blown
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@code{gpg} and uses a different (and simpler) way to check that
the public keys used to make the signature are valid. There are
no configuration files and only a few options are implemented.
@code{@gpgvname} assumes that all keys in the keyring are trustworthy.
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That does also mean that it does not check for expired or revoked
keys.
By default a keyring named @file{trustedkeys.gpg} is used. This
default keyring is assumed to be in the home directory of GnuPG,
either the default home directory or the one set by an option or an
environment variable. The option @code{--keyring} may be used to
specify a different keyring or even multiple keyrings.
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@noindent
@mansect options
@code{@gpgvname} recognizes these options:
@table @gnupgtabopt
@item --verbose
@itemx -v
@opindex verbose
Gives more information during processing. If used
twice, the input data is listed in detail.
@item --quiet
@itemx -q
@opindex quiet
Try to be as quiet as possible.
@item --keyring @var{file}
@opindex keyring
Add @var{file} to the list of keyrings.
If @var{file} begins with a tilde and a slash, these
are replaced by the HOME directory. If the filename
does not contain a slash, it is assumed to be in the
home-directory ("~/.gnupg" if --homedir is not used).
@item --status-fd @var{n}
@opindex status-fd
Write special status strings to the file descriptor @var{n}. See the
file DETAILS in the documentation for a listing of them.
@item --logger-fd @code{n}
@opindex logger-fd
Write log output to file descriptor @code{n} and not to stderr.
@item --ignore-time-conflict
@opindex ignore-time-conflict
GnuPG normally checks that the timestamps associated with keys and
signatures have plausible values. However, sometimes a signature seems to
be older than the key due to clock problems. This option turns these
checks into warnings.
@include opt-homedir.texi
gpg: Add option --weak-digest to gpg and gpgv. * g10/options.h: Add weak_digests linked list to opts. * g10/main.h: Declare weakhash linked list struct and additional_weak_digest() function to insert newly-declared weak digests into opts. * g10/misc.c: (additional_weak_digest): New function. (print_digest_algo_note): Check for deprecated digests. * g10/sig-check.c: (do_check): Reject all weak digests. * g10/gpg.c: Add --weak-digest option to gpg. * doc/gpg.texi: Document gpg --weak-digest option. * g10/gpgv.c: Add --weak-digest option to gpgv. * doc/gpgv.texi: Document gpgv --weak-digest option. -- gpg and gpgv treat signatures made over MD5 as unreliable, unless the user supplies --allow-weak-digests to gpg. Signatures over any other digest are considered acceptable. Despite SHA-1 being a mandatory-to-implement digest algorithm in RFC 4880, the collision-resistance of SHA-1 is weaker than anyone would like it to be. Some operators of high-value targets that depend on OpenPGP signatures may wish to require their signers to use a stronger digest algorithm than SHA1, even if the OpenPGP ecosystem at large cannot deprecate SHA1 entirely today. This changeset adds a new "--weak-digest DIGEST" option for both gpg and gpgv, which makes it straightforward for anyone to treat any signature or certification made over the specified digest as unreliable. This option can be supplied multiple times if the operator wishes to deprecate multiple digest algorithms, and will be ignored completely if the operator supplies --allow-weak-digests (as before). MD5 is always considered weak, regardless of any further --weak-digest options supplied. Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net> (this is a rough cherry-pick of applying the following commits to STABLE-BRANCH-1-4: 76afaed65e3b0ddfa4923cb577ada43217dd4b18 b98939812abf6c643c752ce7c325f98039a1a9e2 91015d021b3dcbe21ad0e580a4f34c523abf9e72 )
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@item --weak-digest @code{name}
@opindex weak-digest
Treat the specified digest algorithm as weak. Signatures made over
weak digests algorithms are normally rejected. This option can be
supplied multiple times if multiple algorithms should be considered
weak. MD5 is always considered weak, and does not need to be listed
explicitly.
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@end table
@mansect return value
The program returns 0 if everything is fine, 1 if at least
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one signature was bad, and other error codes for fatal errors.
@mansect examples
@subsection Examples
@table @asis
@item @gpgvname @code{pgpfile}
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@itemx @gpgvname @code{sigfile} [@code{datafile}]
Verify the signature of the file. The second form is used for detached
signatures, where @code{sigfile} is the detached signature (either
ASCII-armored or binary) and @code{datafile} contains the signed data;
if @code{datafile} is "-" the signed data is expected on
@code{stdin}; if @code{datafile} is not given the name of the file
holding the signed data is constructed by cutting off the extension
(".asc", ".sig" or ".sign") from @code{sigfile}.
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@end table
@mansect environment
@subsection Environment
@table @asis
@item HOME
Used to locate the default home directory.
@item GNUPGHOME
If set directory used instead of "~/.gnupg".
@end table
@mansect files
@subsection FILES
@table @asis
@item ~/.gnupg/trustedkeys.gpg
The default keyring with the allowed keys.
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@end table
@mansect see also
@command{gpg2}(1)
@include see-also-note.texi