ckpasswd - nnrpd password authenticator
ckpasswd [
-gs] [
-d database] [
-f
filename] [
-u username -p password]
ckpasswd is the basic password authenticator for
nnrpd, suitable
for being run from an auth stanza in
readers.conf. See
readers.conf(5) for more information on how to configure an
nnrpd authenticator.
ckpasswd accepts a username and password from
nnrpd and tells
nnrpd(8) whether that's the correct password for that username. By
default, when given no arguments, it tries to check the password using PAM if
support for PAM was found when INN was built. Failing that, it tries to check
the password against the password field returned by
getpwnam(3). Note
that these days most systems no longer make real passwords available via
getpwnam(3) (some still do if and only if the program calling
getpwnam(3) is running as root).
When using PAM,
ckpasswd identifies itself as "nnrpd", not as
"ckpasswd", and the PAM configuration must be set up accordingly.
The details of PAM configuration are different on different operating systems
(and even different Linux distributions); see "EXAMPLES" below for
help getting started, and look for a
pam(7) or
pam.conf(4)
manual page on your system.
When using any method other than PAM,
ckpasswd expects all passwords to
be stored encrypted by the system
crypt(3) function and calls
crypt(3) on the supplied password before comparing it to the expected
password. Any password hashing algorithm supported by your libc or libcrypt
can be used.
-
-d database
- Read passwords from a database (ndbm, gdbm or dbm format
depending on what your system has) rather than by using
getpwnam(3). ckpasswd expects database.dir and
database.pag to exist and to be a database keyed by username with
the encrypted passwords as the values.
While INN doesn't come with a program intended specifically to create such
databases, on most systems it's fairly easy to write a Perl script to do
so. Something like:
#!/usr/bin/perl
use NDBM_File;
use Fcntl;
tie (%db, 'NDBM_File', '/path/to/database', O_RDWR|O_CREAT, 0640)
or die "Cannot open /path/to/database: $!\n";
$| = 1;
print "Username: ";
my $user = <STDIN>;
chomp $user;
print "Password: ";
my $passwd = <STDIN>;
chomp $passwd;
my @alphabet = ('.', '/', 0..9, 'A'..'Z', 'a'..'z');
my $salt = join '', @alphabet[rand 64, rand 64];
$db{$user} = crypt ($passwd, $salt);
untie %db;
Note that this will echo back the password when typed; there are obvious
improvements that could be made to this, but it should be a reasonable
start. Sometimes a program like this will be available with the name
dbmpasswd.
This option will not be available on systems without ndbm, gdbm or dbm
libraries.
-
-f filename
- Read passwords from the given file rather than using
getpwnam(3). Each line of the file should look something like:
username:$5$Hlb2yXPd$2nOO/QR9P1mnRFr/i6L9ybxbgSDXd4UlatKqbcY4eoB
joe:FCjOJnpOo50IE:Old weak hash algorithm used for Joe
Each line has at least two fields separated by a colon. The first field
contains the username; the second field contains a password hashed with
the crypt(3) function. Additional colons and data may appear after
the encrypted password; that data will be ignored by ckpasswd.
Lines starting with a number sign ("#") are ignored.
INN does not come with a utility to create the encrypted passwords, but
OpenSSL can do so and it's also a quick job with Perl (see the one-line
example script below).
A line in filename for the user "user" with the password
"pass" would be "user:" followed with the output of
the following command using SHA-256 as hashing scheme:
% openssl passwd -5 pass
$5$UIhtJSBOaC0Ap3Vk$nbKgmykshoQ2HmvA3s/nI.X4uhhNHBKTYhBS3pYLjJ6
See the openssl-passwd(1) man page for the list of hashing schemes it
can generate. You must take one that your system crypt(3) function
handles (type "man 3 crypt" or "man 5 crypt" to find
the supported hashing schemes).
In case OpenSSL is not installed on your server, you can also use the
following Perl command which does the same job with SHA-256 (see details
below to set "YourSalt" to an appropriate value; 5 is the prefix
for SHA-256, which does not expect any parameters):
% perl -le 'print crypt("pass", q{$5$YourSalt$})'
$5$YourSalt$V5hqwFg1nhKb5as6md9KTe5b2NyavsMS6dBYVKfp5W7
As Perl makes use of crypt(3), you have access to all available
hashing schemes on your systems. For instance, if yescript is supported,
you can generate an encrypted password with an argument like
"$y$j9T$YourSalt$" to Perl crypt function, where "y"
is the prefix for yescript, "j9T" the parameters passed to
crypt_gensalt(3) to generate the hashed password (these parameters
control the yescript configuration, and correspond in this example to the
"YESCRYPT_DEFAULTS" flag, the recommended flavor which has
"j" value in 2023, with cost factor of 4096 as block count and
32 as block size) and "YourSalt" a string which should be chosen
at random and different for each user. The syntax and optimal length of
the salt depend on the hashing scheme (e.g. a length multiple of 4 for
yescript) and cryptographic recommendations (e.g. at least 32 random bits
in length, following NIST SP 800-63B recommendations in 2023).
To put it in a nutshell, in the following command, you only have to change
the password "pass" and the "YourSalt" random string,
different for each user, and leave the rest of the command as-is:
% perl -le 'print crypt("pass", q{$y$j9T$YourSalt$})'
$y$j9T$YourSalt$X4tB48vKNDT6mK0vNOc7ppKPWvEsyMg5LwoQfO50r2A
A random salt of 12 characters can be obtained with the following command
(the result corresponds to 72 random bits as each character is selected in
a 6-bit range of 64 possible characters):
% perl -le 'print join("",
(".", "/", 0..9, A..Z, a..z)[map {rand 64} (1..12)])'
k2W/17eJu58r
- -g
- Attempt to look up system group corresponding to username
and return a string like "user@group" to be matched against in
readers.conf. This option is incompatible with the -d and
-f options.
-
-p password
- Use password as the password for authentication
rather than reading a password using the nnrpd authenticator
protocol. This option is useful only for testing your authentication
system (particularly since it involves putting a password on the command
line), and does not work when ckpasswd is run by nnrpd. If
this option is given, -u must also be given.
- -s
- Check passwords against the result of getspnam(3)
instead of getpwnam(3). This function, on those systems that
supports it, reads from /etc/shadow or similar more restricted
files. If you want to check passwords supplied to nnrpd(8) against
system account passwords, you will probably have to use this option on
most systems.
Most systems require special privileges to call getspnam(3), so in
order to use this option you may need to make ckpasswd setgid to
some group (like group "shadow") or even setuid root.
ckpasswd has not been specifically audited for such uses! It is,
however, a very small program that you should be able to check by hand for
security.
This configuration is not recommended if it can be avoided, for serious
security reasons. See "SECURITY CONSIDERATIONS" in
readers.conf(5) for discussion.
-
-u username
- Authenticate as username. This option is useful only
for testing (so that you can test your authentication system easily) and
does not work when ckpasswd is run by nnrpd. If this option
is given, -p must also be given.
See
readers.conf(5) for examples of
nnrpd(8) authentication
configuration that uses
ckpasswd to check passwords.
An example PAM configuration for
/etc/pam.conf that tells
ckpasswd
to check usernames and passwords against system accounts is:
nnrpd auth required pam_unix.so
nnrpd account required pam_unix.so
Your system may want you to instead create a file named
nnrpd in
/etc/pam.d with lines like:
auth required pam_unix.so
account required pam_unix.so
This is only the simplest configuration. You may be able to include common
shared files, and you may want to stack other modules, either to allow
different authentication methods or to apply restrictions like lists of users
who can't authenticate using
ckpasswd. The best guide is the
documentation for your system and the other PAM configurations you're already
using.
To test to make sure that
ckpasswd is working correctly, you can run it
manually and then give it the username (prefixed with
"ClientAuthname:") and password (prefixed with
"ClientPassword:") on standard input. For example:
(echo 'ClientAuthname: test' ; echo 'ClientPassword: testing') \
| ckpasswd -f /path/to/passwd/file
will check a username of "test" and a password of "testing"
against the username and passwords stored in
/path/to/passwd/file. On
success,
ckpasswd will print "User:test" and exit with status
0. On failure, it will print some sort of error message and exit a non-zero
status.
Written by Russ Allbery <
[email protected]> for InterNetNews.
crypt(3),
nnrpd(8),
pam(7),
readers.conf(5).