Provided by: inn2_2.7.3-1_amd64 
NAME
ckpasswd - nnrpd password authenticator
SYNOPSIS
ckpasswd [-gs] [-d database] [-f filename] [-u username -p password]
DESCRIPTION
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.
OPTIONS
-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.
EXAMPLES
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.
HISTORY
Written by Russ Allbery <eagle@eyrie.org> for InterNetNews.
SEE ALSO
crypt(3), nnrpd(8), pam(7), readers.conf(5).
INN 2.7.3 2025-05-19 CKPASSWD(8)