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如何設(shè)置PAM模塊控制Linux密碼策略 時(shí)間：2015-06-28 00:00:00 來源：IT貓撲網(wǎng) 作者：網(wǎng)管聯(lián)盟 我要評(píng)論(0)

　　我們?cè)谑褂?a href="http://m.ygkjgt7.cn/key/linuxxitong/" target="_blank">linux系統(tǒng)設(shè)置密碼的時(shí)候，經(jīng)常遇到這樣的問題，系統(tǒng)提示：您的密碼太簡(jiǎn)單，或者您的密碼是字典的一部分。那么系統(tǒng)是如何實(shí)現(xiàn)對(duì)用戶的密碼的復(fù)雜度的檢查的呢？

　　系統(tǒng)對(duì)密碼的控制是有兩部分(我知道的)組成：

　　1 cracklib

　　2 login.defs

　　聲明：login.defs主要是控制密碼的有效期。對(duì)密碼進(jìn)行時(shí)間管理。此處不細(xì)談

　　pam_cracklib.so 才是控制密碼復(fù)雜度的關(guān)鍵文件

　　redhat公司專門開發(fā)了cracklib這個(gè)安裝包來判斷密碼的復(fù)雜度

　　可以rpm -ql cracklib查看

　　密碼的復(fù)雜度的判斷是通過pam模塊控制來實(shí)現(xiàn)的，具體的模塊是pam_cracklibpam_cracklib 的參數(shù)介紹：

　　debug

　　This option makes the module write information to syslog(3) indicating the behavior of the module (this option does not write password information to the log file).

　　type=XXX

　　The default action is for the module to use the following prompts when requesting passwords: "New UNIX password: " and "Retype UNIX password: ". The default word UNIX can be replaced with this option.

　　retry=N

　　Prompt user at most N times before returning with error. The default is 1

　　difok=N

　　This argument will change the default of 5 for the number of characters in the new password that must not be present in the old password. In addition, if 1/2 of the characters in the new password are different then the new password will be accepted anyway.

　　difignore=N

　　How many characters should the password have before difok will be ignored. The default is 23.

　　minlen=N

　　The minimum acceptable size for the new password (plus one if credits are not disabled which is the default). In addition to the number of characters in the new password, credit (of +1 in length) is given for each different kind of character (other, upper, lower and digit). The default for this parameter is 9 which is good for a old style UNIX password all of the same type of character but may be too low to exploit the added security of a md5 system. Note that there is a pair of length limits in Cracklib itself, a "way too short" limit of 4 which is hard coded in and a defined limit (6) that will be checked without reference to minlen. If you want to allow passwords as short as 5 characters you should not use this module.

　　dcredit=N

　　(N >= 0) This is the maximum credit for having digits in the new password. If you have less than or N digits, each digit will count +1 towards meeting the current minlen value. The default for dcredit is 1 which is the recommended value for minlen less than 10.

　　(N < 0) This is the minimum number of digits that must be met for a new password.

　　ucredit=N

　　(N >= 0) This is the maximum credit for having upper case letters in the new password. If you have less than or N upper case letters each letter will count +1 towards meeting the current minlen value. The default for ucredit is 1 which is the recommended value for minlen less than 10.

　　(N > 0) This is the minimum number of upper case letters that must be met for a new password.

　　lcredit=N

　　(N >= 0) This is the maximum credit for having lower case letters in the new password. If you have less than or N lower case letters, each letter will count +1 towards meeting the current minlen value. The default for lcredit is 1 which is the recommended value for minlen less than 10.

　　(N < 0) This is the minimum number of lower case letters that must be met for a new password.

#p#副標(biāo)題#e#

　　ocredit=N

　　(N >= 0) This is the maximum credit for having other characters in the new password. If you have less than or N other characters, each character will count +1 towards meeting the current minlen value. The default for ocredit is 1 which is the recommended value for minlen less than 10.

　　(N < 0) This is the minimum number of other characters that must be met for a new password.

　　use_authtok

　　This argument is used to force the module to not prompt the user for a new password but use the one provided by the previously stacked password module.

　　dictpath=/path/to/dict

　　Path to the cracklib dictionaries.

　　dictpath=/path/to/dict //注：密碼字典，這個(gè)是驗(yàn)證用戶的密碼是否是字典一部分的關(guān)鍵。

　　Path to the cracklib dictionaries.

　　cracklib密碼強(qiáng)度檢測(cè)過程

　　首先檢查密碼是否是字典的一部分，如果不是，則進(jìn)行下面的檢查

　　密碼強(qiáng)度檢測(cè)過程

　　These checks are:

　　Palindrome

　　Is the new password a palindrome of the old one?

　　新密碼是否舊密碼的回文

　　Case Change Only

　　Is the new password the the old one with only a change of case?

　　新密碼是否只是就密碼改變了大小寫

　　Similar

　　Is the new password too much like the old one?

　　新密碼是否和舊密碼很相似

　　This is primarily controlled by one argument, difok which is a number of characters that if different between the old and new are enough to accept the new password, this defaults to 10 or 1/2 the size of the new password whichever is smaller.

　　To avoid the lockup associated with trying to change a long and complicated password, difignore is available. This argument can be used to specify the minimum length a new password needs to be before the difok value is ignored. The default value for difignore is 23.

　　Simple

　　Is the new password too small?

　　新密碼是否太短

　　This is controlled by 5 arguments minlen, dcredit, ucredit, lcredit, and ocredit. See the section on the arguments for the details of how these work and there defaults.

　　Rotated

　　Is the new password a rotated version of the old password?

　　新密碼的字符是否是舊密碼字符的一個(gè)循環(huán)

　　例如舊密碼：123

　　新密碼：231

　　Already used

　　Was the password used in the past?

　　這個(gè)密碼以前是否使用過

　　Previously used passwords are to be found in /etc/security/opasswd.

　　那么系統(tǒng)是如何實(shí)現(xiàn)這個(gè)控制的呢？

　　在系統(tǒng)的配置文件/etc/pam.d/system-auth 中有這樣一行

　　password requisite???? pam_cracklib.so try_first_pass retry=3

　　我們可以根據(jù)pam_cracklib的參數(shù)這樣配置這個(gè)pam模塊來達(dá)到我們想要的目的

　　password required /lib/security/pam_cracklib.so retry=3 type= minlen=8 difok=3 dictpath=/path/to/dict

關(guān)鍵詞標(biāo)簽：Linux密碼策略

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