Introduction to CrackLib

The CrackLib package contains a library used to enforce strong passwords by comparing user selected passwords to words in chosen word lists.

1、在设置密码时，系统会提示：It's bad password! It's way too short!这些bad password存储在哪里呢？

2、/usr/lib/cracklib_dict.pwd密码字典

linux系统中有个字典文件叫/usr/lib/cracklib_dict.pwd，使用这个文件中记录的字符作为密码，系统都会提示密码太简单！

3、相关网址
http://www.linuxfromscratch.org/blfs/view/stable/postlfs/cracklib.html
http://downloads.sourceforge.net/cracklib/cracklib-words-20080203.gz
http://downloads.sourceforge.net/cracklib/cracklib-2.8.12.tar.gz

4、安装
#####################################################################################
./configure --prefix=/usr \
--with-default-dict=/lib/cracklib/pw_dict &&
make

make install &&
mv -v /usr/lib/libcrack.so.2* /lib &&
ln -v -sf ../../lib/libcrack.so.2.8.0 /usr/lib/libcrack.so
install -v -m644 -D ../cracklib-words-20080203.gz \
/usr/share/dict/cracklib-words.gz &&
gunzip -v /usr/share/dict/cracklib-words.gz &&
ln -v -s cracklib-words /usr/share/dict/words &&
echo $(hostname) >>/usr/share/dict/cracklib-extra-words &&
install -v -m755 -d /lib/cracklib &&
create-cracklib-dict /usr/share/dict/cracklib-words \
/usr/share/dict/cracklib-extra-words

create-cracklib-dict: This command creates the CrackLib dictionary from the word lists. Modify the command to add any

additional word lists you have installed.

#####################################################################################

5、strings /usr/lib/cracklib_dict.pwd >> passwd.txt提取密码

6、gzip -d cracklib-2.8.12.tar.gz

grep password cracklib-words-20080203
john -w:cracklib-words-20080203 a.txt

7、cracklib原理
#ifndef CRACKLIB_DICTPATH
　　#define CRACKLIB_DICTPATH "/usr/local/lib/pw_dict"
　　#endif
　　...
　　...
　　...
　　char *msg;
　　while(1) {
　　passbuf = getpass("请设定新密码:");
　　if (!*passbuf) {
　　(void)printf("密码设定取消, 继续使用旧密码\n");
　　break;
　　}
　　if (strlen(pussbuf) <= 4 ││ !strcmp( passbuf, newuser.userid ) ) { 　　(void)printf("密码太短或与使用者代号相同, 请重新输入\n "); 　　continue; 　　} 　　if (msg = (char*) FascistCheck(passbuf, CRACKLIBPATH)) { 　　printf("请另选密码! (%s)\n",msg); 　　continue; 　　} 　　strncpy( newuser.passwd, passbuf, PASSLEN ); 　　passbuf = getpass("请再输入一次你的密码 ); 　　if( strncmp( passbuf, newuser.passwd, PASSLEN ) != 0 ) { 　　prints("密码输入错误, 请重新输入密码.\n") ; 　　continue; 　　} 　　passbuf[8] = '\0' ; 　　break; 　　}

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