Provided by: inn2_2.7.3~20241006-1_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).