(gnupg1.info.gz) GPG Examples
Info Catalog
(gnupg1.info.gz) GPG Configuration
(gnupg1.info.gz) Invoking GPG
1.4 Examples
============
gpg -se -r `Bob' `file'
sign and encrypt for user Bob
gpg -clearsign `file'
make a clear text signature
gpg -sb `file'
make a detached signature
gpg -list-keys `user_ID'
show keys
gpg -fingerprint `user_ID'
show fingerprint
gpg -verify `pgpfile'
gpg -verify `sigfile'
Verify the signature of the file but do not output the data. The
second form is used for detached signatures, where `sigfile' is
the detached signature (either ASCII armored or binary) and are
the signed data; if this is not given, the name of the file
holding the signed data is constructed by cutting off the
extension (".asc" or ".sig") of `sigfile' or by asking the user
for the filename.
RETURN VALUE
************
The program returns 0 if everything was fine, 1 if at least a signature
was bad, and other error codes for fatal errors.
WARNINGS
********
Use a *good* password for your user account and a *good* passphrase to
protect your secret key. This passphrase is the weakest part of the
whole system. Programs to do dictionary attacks on your secret keyring
are very easy to write and so you should protect your "~/.gnupg/"
directory very well.
Keep in mind that, if this program is used over a network (telnet),
it is *very* easy to spy out your passphrase!
If you are going to verify detached signatures, make sure that the
program knows about it; either give both filenames on the command line
or use `-' to specify stdin.
INTEROPERABILITY WITH OTHER OPENPGP PROGRAMS
********************************************
GnuPG tries to be a very flexible implementation of the OpenPGP
standard. In particular, GnuPG implements many of the optional parts of
the standard, such as the SHA-512 hash, and the ZLIB and BZIP2
compression algorithms. It is important to be aware that not all
OpenPGP programs implement these optional algorithms and that by
forcing their use via the `--cipher-algo', `--digest-algo',
`--cert-digest-algo', or `--compress-algo' options in GnuPG, it is
possible to create a perfectly valid OpenPGP message, but one that
cannot be read by the intended recipient.
There are dozens of variations of OpenPGP programs available, and
each supports a slightly different subset of these optional algorithms.
For example, until recently, no (unhacked) version of PGP supported the
BLOWFISH cipher algorithm. A message using BLOWFISH simply could not be
read by a PGP user. By default, GnuPG uses the standard OpenPGP
preferences system that will always do the right thing and create
messages that are usable by all recipients, regardless of which OpenPGP
program they use. Only override this safe default if you really know
what you are doing.
If you absolutely must override the safe default, or if the
preferences on a given key are invalid for some reason, you are far
better off using the `--pgp6', `--pgp7', or `--pgp8' options. These
options are safe as they do not force any particular algorithms in
violation of OpenPGP, but rather reduce the available algorithms to a
"PGP-safe" list.
BUGS
****
On many systems this program should be installed as setuid(root). This
is necessary to lock memory pages. Locking memory pages prevents the
operating system from writing memory pages (which may contain
passphrases or other sensitive material) to disk. If you get no warning
message about insecure memory your operating system supports locking
without being root. The program drops root privileges as soon as locked
memory is allocated.
Note also that some systems (especially laptops) have the ability to
"suspend to disk" (also known as "safe sleep" or "hibernate"). This
writes all memory to disk before going into a low power or even powered
off mode. Unless measures are taken in the operating system to protect
the saved memory, passphrases or other sensitive material may be
recoverable from it later.
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(gnupg1.info.gz) GPG Configuration
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