netpgp(1)
- NetBSD Manual Pages
NETPGP(1) NetBSD General Commands Manual NETPGP(1)
NAME
netpgp -- signing, verification, encryption, and decryption utility
SYNOPSIS
netpgp --encrypt [--output=filename] [options] file ...
netpgp --decrypt [--output=filename] [--pass-fd=fd]
[--num-tries=attempts] [options] file ...
netpgp --sign [--armor] [--detach] [--hash=algorithm] [--output=filename]
[--pass-fd=fd] [--from=sig-valid-from] [--num-tries=attempts]
[--duration=sig-valid-duration] [options] file ...
netpgp --verify [options] file ...
netpgp --cat [--output=filename] [options] file ...
netpgp --clearsign [--output=filename] [--pass-fd=fd] [options] file ...
netpgp --list-packets [--pass-fd=fd] file ...
netpgp --version
netpgp [-Vdesv] [-olong-option=value] file ...
where the long options for all commands are:
[--cipher=ciphername]
[--coredumps]
[--homedir=home-directory]
[--keyring=keyring]
[--results=filename]
[--ssh-keys]
[--userid=userid]
[--verbose]
DESCRIPTION
The netpgp command can digitally sign files and verify that the signa-
tures attached to files were signed by a given user identifier. netpgp
can also encrypt files using the public or private keys of users and, in
the same manner, decrypt files which were encrypted.
For signing and encryption, a unique identity is needed. This identity
is made up of a private and public key. The public key part is made
available and known to everyone. The private key is kept secret, and
known only to the user who created the identity. The secret key is pro-
tected with a passphrase.
In rough terms, a digital signature is a digest of a file's contents,
encrypted with the user's private key. Since together, the private and
public keys identify the user uniquely, the signature can be used to
identify the exact version of the file, and any changes made to the file
will mean that the signature no longer matches.
As a corollary, the file can be transformed using a user's public key,
into text such that the contents can only be viewed by someone with the
corresponding private key. This is called encryption.
To manipulate keys themselves, a separate utility is provided, called
netpgpkeys(1).
Keyrings are collections of public keys belonging to other users. By
using other means of identification, it is possible to establish the bona
fides of other users. Once trust has been established, the public key of
the other user will be signed. The other user's public key can be added
to our keyring. The other user will add our public key to their keyring.
Keys can be listed, exported (i.e. made available to others), and
imported (i.e. users who have signed our public key).
The --list-packets command can be used for debugging purposes.
The following commands are used to sign and verify signatures:
--cat The signature of the signed file named on the command line
is verified against the contents of the file itself. If
the two match, then the original contents are sent to stan-
dard out. If the signature does not match, no output is
generated.
--clearsign The signature of the file named on the command line is cal-
culated in the same manner as the --sign command, but the
text is added to the file such that the text itself is not
in binary format, but can be read by mere mortals.
--sign The private key is used to digitally sign the files named
on the command line. The file and its attached signature
are created with a ``.gpg'' extension to the original file
name. The user will be prompted for their pass phrase
using getpass(3).
--verify For each of the files named on the command line, the signa-
ture of the file is verified, checking the contents against
the user's public signature.
The following commands can be used to encrypt and decrypt files:
--decrypt Decrypt the file using the user's private key. The pass
phrase will be obtained by prompting the user to type it
in, using getpass(3).
--encrypt Use the user's public key to encrypt the files named on the
command line.
--list-packets
List all the ``packets'' in an encrypted or signed file.
Internally, netpgp splits an encrypted or signed file into
separate packets, and this option is used to give a verbose
representation of these packets on standard output.
--version Print the version information from the libnetpgp(3)
library.
In addition to one of the preceding commands, a number of qualifiers or
options may be given.
--armour, --armor
This option, however it is spelled, wraps the signature as
an ASCII-encoded piece of text, for ease of use.
--cipher ciphername
can be used to specify the symmetric encryption algorithm
(or cipher) which is used when encrypting data. To decrypt
this data, the same cipher will be needed, so care should
be taken at encryption time to make sure that the person
who decrypts the data has access to the cipher used. The
default cipher algorithm is the ``CAST5'' algorithm.
--detach, --detached
When signing a file, place the resulting signature in a
separate file from the one being signed.
--hash-alg hash-algorithm
can be used to specify the hash algorithm (sometimes called
a digest algorithm) which is used with RSA keys when sign-
ing text. The default hash algorithm is the ``SHA256''
algorithm. At the present time, ``SHA1'' may also be used,
although it is recommended that SHA256 be used, due to
recent advances in generating collisions for the SHA1 hash-
ing algorithm.
--homedir home-directory
Keyrings are normally located, for historical reasons,
within the user's home directory in a subdirectory called
``.gnupg'' and this option specifies an alternative loca-
tion in which to find that sub-directory.
--keyring keyring
This option specifies an alternative keyring to be used.
All keyring operations will be relative to this alternative
keyring.
--output specifies a filename to which verified output from a signed
file may be redirected. The default is to send the veri-
fied output to stdout, and this may also be specified using
the ``-'' value.
--results filename
specifies a filename to which the results of the operation
should be sent. The default is to send the results to
stderr.
--ssh-keys specifies that the public and private keys should be taken
from the ssh(1) host key files, usually found in
/etc/ssh/ssh_host_rsa_key and /etc/ssh/ssh_host_rsa_key.pub
for the private and public host keys.
--userid userid
This option specifies the user identity to be used for all
operations. This identity can either be in the form of the
full name, or as an email address. Care should be exer-
cised with these ways of specifying the user identity,
since the netpgp utility has no way of verifying that an
email address is valid, or that a key belongs to a certain
individual. The trust for a signed key is given by the
other signers of that key. The 16 hexadecimal digit user
identity should be used when specifying user identities
--email addresses and names are provided as aliases.
--pass-fd=fd This option is intended for the use of external programs
which may like to use the libnetpgp(3) library through the
netpgp interface, but have their own ways of retrieving and
caching the passphrase for the secret key. In this case,
the netpgp utility will read a line of text from the file
descriptor passed to it in the command line argument,
rather than using its own methods of retrieving the
passphrase from the user.
--num-tries=attempts
This option sets the maximum number of attempts to get the
correct passphrase from the user. A value of unlimited
means that there is no maximum number of attempts, and the
utility will loop endlessly until the correct passphrase
has been entered, or the utility is terminated.
--from=signature-valid-from
This option allows the signer to specify a time as the
starting point for validity of the signature. In this way
it is possible to prevent files from being verified until a
specific point in time. The time can be specified either
in YYYY-MM-DD format, or as the number of seconds since the
epoch.
--duration=signature-valid-to
This option allows the signer to specify a time as the end
point for validity of the signature. In this way it is
possible to prevent files from being verified after a spe-
cific point in time. The time can be specified either in
YYYY-MM-DD format, or as the number of seconds.
--verbose This option can be used to view information during the
process of the netpgp requests.
--coredumps in normal processing, if an error occurs, the contents of
memory are saved to disk, and can be read using tools to
analyse behaviour. Unfortunately this can disclose infor-
mation to people viewing the core dump, such as secret
keys, and passphrases protecting those keys. In normal
operation, netpgp will turn off the ability to save core
dumps on persistent storage, but selecting this option will
allow core dumps to be written to disk. This option should
be used wisely, and any core dumps should be deleted in a
secure manner when no longer needed.
PASS PHRASES
At the present time, the pass phrase cannot be changed by netpgpkeys(1)
once it has been chosen, and will be used for the life of the key, so a
wise choice is advised. The pass phrase should not be an easily guess-
able word or phrase, or related to information that can be gained through
``social engineering'' using search engines, or other public information
retrieval methods.
getpass(3) will be used to obtain the pass phrase from the user if it is
needed, such as during signing or encryption, or key generation, so that
any secret information cannot be viewed by other users using the ps(1) or
top(1) commands, or by looking over the shoulder at the screen.
Since the public and private key pair can be used to verify a person's
identity, and since identity theft can have far-reaching consequences,
users are strongly encouraged to enter their pass phrases only when
prompted by the application.
SIGNING AND VERIFICATION
Signing and verification of a file is best viewed using the following
example:
% netpgp --sign --userid=agc@netbsd.org a
pub 2048/RSA (Encrypt or Sign) 1b68dcfcc0596823 2004-01-12
Key fingerprint: d415 9deb 336d e4cc cdfa 00cd 1b68 dcfc c059 6823
uid Alistair Crooks <agc@netbsd.org>
uid Alistair Crooks <agc@pkgsrc.org>
uid Alistair Crooks <agc@alistaircrooks.com>
uid Alistair Crooks <alistair@hockley-crooks.com>
netpgp passphrase:
% netpgp --verify a.gpg
Good signature for a.gpg made Thu Jan 29 03:06:00 2009
using RSA (Encrypt or Sign) key 1B68DCFCC0596823
pub 2048/RSA (Encrypt or Sign) 1b68dcfcc0596823 2004-01-12
Key fingerprint: d415 9deb 336d e4cc cdfa 00cd 1b68 dcfc c059 6823
uid Alistair Crooks <alistair@hockley-crooks.com>
uid Alistair Crooks <agc@pkgsrc.org>
uid Alistair Crooks <agc@netbsd.org>
uid Alistair Crooks <agc@alistaircrooks.com>
%
In the example above, a signature is made on a single file called ``a''
using a user identity corresponding to ``agc@netbsd.org'' The key located
for the user identity is displayed, and the user is prompted to type in
their passphrase. The resulting file, called ``a.gpg'' is placed in the
same directory. The second part of the example shows a verification of
the signed file taking place. The time and user identity of the signa-
tory is displayed, followed by a fuller description of the public key of
the signatory. In both cases, the exit value from the utility was a suc-
cessful one.
If a detached signature of a file called ``a'' is requested, the signa-
ture would be placed in a file called ``a.sig''.
To encrypt a file, the user's public key is used. Subsequent decryption
of the file requires that the secret key is known. When decrypting, the
key is displayed, and the passphrase protecting the secret key must be
typed in to access the data in the encrypted file.
% netpgp --encrypt --userid=c0596823 a
% netpgp --decrypt a.gpg
pub 2048/RSA (Encrypt or Sign) 1b68dcfcc0596823 2004-01-12
Key fingerprint: d415 9deb 336d e4cc cdfa 00cd 1b68 dcfc c059 6823
uid Alistair Crooks <agc@netbsd.org>
uid Alistair Crooks <agc@pkgsrc.org>
uid Alistair Crooks <agc@alistaircrooks.com>
uid Alistair Crooks <alistair@hockley-crooks.com>
netpgp passphrase:
%
If no file name is provided, the data will be read from standard input,
and displayed on standard output:
% netpgp --encrypt < a | netpgp --decrypt > b
netpgp: default key set to "C0596823"
netpgp: default key set to "C0596823"
pub 2048/RSA (Encrypt or Sign) 1b68dcfcc0596823 2004-01-12
Key fingerprint: d415 9deb 336d e4cc cdfa 00cd 1b68 dcfc c059 6823
uid Alistair Crooks <agc@netbsd.org>
uid Alistair Crooks <agc@pkgsrc.org>
uid Alistair Crooks <agc@alistaircrooks.com>
uid Alistair Crooks <alistair@hockley-crooks.com>
netpgp passphrase:
%
This simple (and contrived) example shows that netpgp commands can be
used together in a pipeline to produce the desired effect.
% netpgp --sign < a | netpgp --cat > b
netpgp: default key set to "C0596823"
netpgp: default key set to "C0596823"
pub 2048/RSA (Encrypt or Sign) 1b68dcfcc0596823 2004-01-12
Key fingerprint: d415 9deb 336d e4cc cdfa 00cd 1b68 dcfc c059 6823
uid Alistair Crooks <agc@netbsd.org>
uid Alistair Crooks <agc@pkgsrc.org>
uid Alistair Crooks <agc@alistaircrooks.com>
uid Alistair Crooks <alistair@hockley-crooks.com>
netpgp passphrase:
Good signature for <stdin> made Mon Dec 21 18:25:02 2009
using RSA (Encrypt or Sign) key 1b68dcfcc0596823
pub 2048/RSA (Encrypt or Sign) 1b68dcfcc0596823 2004-01-12
Key fingerprint: d415 9deb 336d e4cc cdfa 00cd 1b68 dcfc c059 6823
uid Alistair Crooks <alistair@hockley-crooks.com>
uid Alistair Crooks <agc@pkgsrc.org>
uid Alistair Crooks <agc@netbsd.org>
uid Alistair Crooks <agc@alistaircrooks.com>
uid Alistair Crooks (Yahoo!) <agcrooks@yahoo-inc.com>
%
For operations like signing and encrypting a file at the same time, the
best way is to make use of pipelines:
% netpgp --sign < example | netpgp --encrypt --userid=c0596823 > example.gpg
netpgp: default key set to "C0596823"
pub 2048/RSA (Encrypt or Sign) 1b68dcfcc0596823 2004-01-12
Key fingerprint: d415 9deb 336d e4cc cdfa 00cd 1b68 dcfc c059 6823
uid Alistair Crooks <alistair@hockley-crooks.com>
uid Alistair Crooks <agc@pkgsrc.org>
uid Alistair Crooks <agc@netbsd.org>
uid Alistair Crooks <agc@alistaircrooks.com>
uid Alistair Crooks (Yahoo!) <agcrooks@yahoo-inc.com>
netpgp passphrase:
% netpgp --decrypt < example.gpg | netpgp --cat
netpgp: default key set to "C0596823"
netpgp: default key set to "C0596823"
pub 2048/RSA (Encrypt or Sign) 1b68dcfcc0596823 2004-01-12
Key fingerprint: d415 9deb 336d e4cc cdfa 00cd 1b68 dcfc c059 6823
uid Alistair Crooks <alistair@hockley-crooks.com>
uid Alistair Crooks <agc@pkgsrc.org>
uid Alistair Crooks <agc@netbsd.org>
uid Alistair Crooks <agc@alistaircrooks.com>
uid Alistair Crooks (Yahoo!) <agcrooks@yahoo-inc.com>
netpgp passphrase:
Good signature for <stdin> made Mon Feb 22 07:21:19 2010
using RSA (Encrypt or Sign) key 1b68dcfcc0596823
pub 2048/RSA (Encrypt or Sign) 1b68dcfcc0596823 2004-01-12
Key fingerprint: d415 9deb 336d e4cc cdfa 00cd 1b68 dcfc c059 6823
uid Alistair Crooks <alistair@hockley-crooks.com>
uid Alistair Crooks <agc@pkgsrc.org>
uid Alistair Crooks <agc@netbsd.org>
uid Alistair Crooks <agc@alistaircrooks.com>
uid Alistair Crooks (Yahoo!) <agcrooks@yahoo-inc.com>
...contents of original file...
%
EXIT STATUS
The netpgp utility will return 0 for success, 1 if the file's signature
does not match what was expected, or 2 if any other error occurs.
SEE ALSO
netpgpkeys(1), ssh(1), getpass(3), libnetpgp(3), ssl(3), zlib(3)
STANDARDS
J. Callas, L. Donnerhacke, H. Finney, D. Shaw, and R. Thayer, OpenPGP
Message Format, RFC 4880, November 2007.
HISTORY
The netpgp command first appeared in NetBSD 6.0.
AUTHORS
Ben Laurie, Rachel Willmer, and overhauled and rewritten by Alistair
Crooks <agc@NetBSD.org>. This manual page was also written by Alistair
Crooks.
NetBSD 9.3 February 16, 2014 NetBSD 9.3
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