Description

pam_captcha - A Visual text-based CAPTCHA challenge module for PAM
Jordan Sissel <jls@semicomplete.com> 

Version 1.5 (July 2010)

Released under the BSD license. 

If you use or make changes to pam_captcha, shoot me an email or something. I
always like to hear how people use my software :) And no, you don't have to
do it. Nor do you have to send me patches, though patches are appreciated.

Requirements:
  - Figlet
  - OpenPAM or Linux-PAM (Linux and FreeBSD known to work)

Notes: 
   - I have tested this in FreeBSD and Linux. It works there.
   - It will not build under Solaris 9, and I have no intentions of
     fixing that at this time

Installation Instructions
  - Just type 'make' (assuming you downloaded the Makefile too)
  - Copy pam_captcha.so to your pam module dir.
      FreeBSD: /usr/lib
      Ubuntu: /lib/security
      Others: Find other files named 'pam_*.so'

  - Place this entry in your pam config for whatever service you want. It
    needs to go at the top of your pam auth stack (first entry?):
 
    auth       requisite     pam_captcha.so    [options]


Available options: math, dda, randomstring
Example:
  - Enable 'math' and 'randomstring' captchas:
    auth       requisite     pam_captcha.so    math randomstring

'requisite' is absolutely necessary here. This keyword means that if a user
fails pam_captcha, the whole auth chain is marked as failure.  This ensure
that users must pass the captcha challenge before being permitted to attempt
any other kind of pam authentication, such as a standard login. 'required'
can work here too but will not break the chain. I like requisite because you
cannot even attempt to authenticate via password if you don't pass the
captcha.

IMPORTANT SSHD_CONFIG NOTE!
  To prevent brute-force scripts from bypassing the pam stack, you MUST
  disable 'password' authentication in your sshd. Disable 'password' auth
  and enable 'keyboard-interactive' instead.

  To do this, put the following in your sshd_config
  PasswordAuthentication no
  ChallengeResponseAuthentication yes

If you use ssh keys to login to your server, you will not be bothered by
pam_captcha becuase publickey authentication does not invoke PAM.

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