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7 .\" ThinkSec AS and NAI Labs, the Security Research Division of Network
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9 .\" ("CBOSS"), as part of the DARPA CHATS research program.
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42 .Nd Password quality-control PAM module
52 module is a simple password strength checking module for
54 In addition to checking regular passwords, it offers support for
55 passphrases and can provide randomly generated passwords.
59 module provides functionality for only one PAM category:
63 parameter, this is the
69 service function will ask the user for a new password, and verify that
70 it meets certain minimum standards.
71 If the chosen password is unsatisfactory, the service function returns
74 The following options may be passed to the authentication module:
75 .Bl -tag -width indent
78 .Cm min No = Ar N0 , N1 , N2 , N3 , N4
82 .Pq Cm min No = Cm disabled , No 24 , 12 , 8 , 7
84 The minimum allowed password lengths for different kinds of
85 passwords/passphrases.
89 disallow passwords of a given kind regardless of their length.
90 Each subsequent number is required to be no larger than the preceding
94 is used for passwords consisting of characters from one character
96 The character classes are: digits, lower-case letters, upper-case
97 letters, and other characters.
98 There is also a special class for
100 characters which could not
101 be classified, but are assumed to be non-digits.
104 is used for passwords consisting of characters from two character
105 classes, which do not meet the requirements for a passphrase.
108 is used for passphrases.
109 A passphrase must consist of sufficient words (see the
116 are used for passwords consisting of characters from three
117 and four character classes, respectively.
119 When calculating the number of character classes, upper-case letters
120 used as the first character and digits used as the last character of a
121 password are not counted.
123 In addition to being sufficiently long, passwords are required to
124 contain enough different characters for the character classes and
125 the minimum length they have been checked against.
127 .It Cm max Ns = Ns Ar N
128 .Pq Cm max Ns = Ns 40
129 The maximum allowed password length.
130 This can be used to prevent users from setting passwords which may be
131 too long for some system services.
132 The value 8 is treated specially: if
134 is set to 8, passwords longer than 8 characters will not be rejected,
135 but will be truncated to 8 characters for the strength checks and the
137 This is for compatibility with the traditional DES password hashes,
138 which truncate the password at 8 characters.
140 It is important that you do set
142 if you are using the traditional
143 hashes, or some weak passwords will pass the checks.
144 .It Cm passphrase Ns = Ns Ar N
145 .Pq Cm passphrase Ns = Ns 3
146 The number of words required for a passphrase, or 0 to disable
148 .It Cm match Ns = Ns Ar N
149 .Pq Cm match Ns = Ns 4
150 The length of common substring required to conclude that a password is
151 at least partially based on information found in a character string,
152 or 0 to disable the substring search.
153 Note that the password will not be rejected once a weak substring is
154 found; it will instead be subjected to the usual strength requirements
155 with the weak substring removed.
157 The substring search is case-insensitive and is able to detect and
158 remove a common substring spelled backwards.
161 .Cm similar No = Cm permit | deny
164 .Pq Cm similar Ns = Ns Cm deny
165 Whether a new password is allowed to be similar to the old one.
166 The passwords are considered to be similar when there is a sufficiently
167 long common substring and the new password with the substring removed
171 .Cm random No = Ar N Op , Cm only
174 .Pq Cm random Ns = Ns 42
175 The size of randomly-generated passwords in bits, or 0 to disable this
177 Passwords that contain the offered randomly-generated string will be
178 allowed regardless of other possible restrictions.
182 modifier can be used to disallow user-chosen passwords.
185 .Cm enforce No = Cm none | users | everyone
188 .Pq Cm enforce Ns = Ns Cm everyone
189 The module can be configured to warn of weak passwords only, but not
190 actually enforce strong passwords.
193 setting will enforce strong passwords for non-root users only.
199 to obtain the user's personal login information and use that during
200 the password strength checks.
201 This behavior can be disabled with the
204 .It Cm retry Ns = Ns Ar N
205 .Pq Cm retry Ns = Ns 3
206 The number of times the module will ask for a new password if the user
207 fails to provide a sufficiently strong password and enter it twice the
209 .It Cm ask_oldauthtok Ns Op = Ns Cm update
210 Ask for the old password as well.
213 leaves this task for subsequent modules.
214 With no argument, the
218 to ask for the old password during the preliminary check phase.
221 option is specified with the
225 will do that during the update phase.
226 .It Cm check_oldauthtok
229 to validate the old password before giving a
231 Normally, this task is left for subsequent modules.
233 The primary use for this option is when
234 .Cm ask_oldauthtok Ns = Ns Cm update
235 is also specified, in which case no other modules gets a chance to ask
236 for and validate the password.
237 Of course, this will only work with
240 .It Cm use_first_pass , use_authtok
241 Use the new password obtained by modules stacked before
243 This disables user interaction within
245 The only difference between
249 is that the former is incompatible with
259 module was written by
260 .An Solar Designer Aq solar@openwall.com .
261 This manual page, derived from the author's documentation, was written
265 ThinkSec AS and NAI Labs, the Security Research Division of Network
266 Associates, Inc.\& under DARPA/SPAWAR contract N66001-01-C-8035
268 as part of the DARPA CHATS research program.