mirror of
https://github.com/Yubico/yubico-pam.git
synced 2024-12-01 15:24:12 +01:00
193 lines
6.6 KiB
Plaintext
193 lines
6.6 KiB
Plaintext
Local Authentication Using Challenge Response
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---------------------------------------------
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The PAM module can utilize the HMAC-SHA1 Challenge-Response mode found
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in YubiKeys starting with version 2.2 for offline authentication.
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This mode is useful if you don't have a stable network connection to
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the YubiCloud.
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The ykpamcfg utility currently outputs the state information to a file
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in the current user's home directory (`$HOME/.yubico/challenge-123456`
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for a YubiKey with serial number API readout enabled, and
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`$HOME/.yubico/challenge` for one without).
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The PAM module supports a system-wide directory for these state files
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(in case the user's home directories are encrypted), but in a system-wide
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directory, the 'challenge' part should be replaced with the
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username. Example: `/var/yubico/alice-123456`.
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To use the system-wide mode, you currently have to move the generated
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state files manually and configure the PAM module accordingly.
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The following process is tested on Ubuntu 12.04.
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First install the package:
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------
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$ sudo apt-get install libpam-yubico
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------
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You will get a question about the PAM configuration line. Enter this
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line:
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------
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mode=challenge-response
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------
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The next question will be about which PAM modules to enable. Don't
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enable anything just yet, because you need to program your YubiKey
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first.
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If you have already installed the package or want to reconfigure it,
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you may use this command:
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------
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$ sudo dpkg-reconfigure libpam-yubico
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------
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The next step is to add a challenge-response slot to your YubiKey. If
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you have a normal YubiKey with OTP functionality on the first slot,
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you could add Challenge-Response on the second slot. You could have
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CR on the first slot, if you want.
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First, program a YubiKey for challenge response on Slot 2:
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------
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$ ykpersonalize -2 -ochal-resp -ochal-hmac -ohmac-lt64 -oserial-api-visible
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...
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Commit? (y/n) [n]: y
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$
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------
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Now, set the current user to require this YubiKey for logon:
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------
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$ mkdir $HOME/.yubico
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$ ykpamcfg -2 -v
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...
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Stored initial challenge and expected response in '/home/alice/.yubico/challenge-123456'.
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$
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------
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From security perspective, it is generally a good idea to move the challenge file in a system-wide path that is only read- and writable by root. To do this do as follow:
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----
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$ sudo mkdir /var/yubico
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$ sudo chown root.root /var/yubico
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$ sudo chmod 700 /var/yubico
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$ ykpamcfg -2 -v
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...
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Stored initial challenge and expected response in '$HOME/.yubico/challenge-123456'.
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$ sudo mv ~/.yubico/challenge-123456 /var/yubico/alice-123456
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$ sudo chown root.root /var/yubico/alice-123456
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$ sudo chmod 600 /var/yubico/alice-123456
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----
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It is important that the file is named with the name of the user that is going to be authenticated by this YubiKey.
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Finally we tell the pam module where to look for the challenge file
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$ emacs /etc/pam.d/common-auth
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and edit the following line as follow:
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auth required pam_yubico.so mode=challenge-response chalresp_path=/var/yubico
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Then back to the PAM configuration step, first make sure you have a
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root terminal available to be able to disable YubiKey login in case of
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issues.
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$ sudo -s
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Then run the "pam-auth-update" command and enable the Yubico PAM
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module.
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$ sudo pam-auth-update
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You should now be able to authenticate using YubiKey
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Challenge-Reseponse together with a password like this:
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----
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jas@latte:~$ sudo -s
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[sudo] password for jas:
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root@latte:~#
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----
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Now remove the YubiKey and try again (in a new terminal to avoid sudo
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caching), and you should not be able to login.
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For debugging, you can make the PAM configuration line:
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mode=challenge-response debug
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and then create a log file:
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----
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# touch /var/run/pam-debug.log
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# chmod go+w /var/run/pam-debug.log
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----
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and then tail the file. For successful logins it should print
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something like this:
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----
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[pam_yubico.c:parse_cfg(721)] called.
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[pam_yubico.c:parse_cfg(722)] flags 32768 argc 2
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[pam_yubico.c:parse_cfg(724)] argv[0]=mode=challenge-response
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[pam_yubico.c:parse_cfg(724)] argv[1]=debug
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[pam_yubico.c:parse_cfg(725)] id=-1
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[pam_yubico.c:parse_cfg(726)] key=(null)
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[pam_yubico.c:parse_cfg(727)] debug=1
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[pam_yubico.c:parse_cfg(728)] alwaysok=0
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[pam_yubico.c:parse_cfg(729)] verbose_otp=0
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[pam_yubico.c:parse_cfg(730)] try_first_pass=0
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[pam_yubico.c:parse_cfg(731)] use_first_pass=0
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[pam_yubico.c:parse_cfg(732)] authfile=(null)
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[pam_yubico.c:parse_cfg(733)] ldapserver=(null)
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[pam_yubico.c:parse_cfg(734)] ldap_uri=(null)
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[pam_yubico.c:parse_cfg(735)] ldapdn=(null)
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[pam_yubico.c:parse_cfg(736)] user_attr=(null)
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[pam_yubico.c:parse_cfg(737)] yubi_attr=(null)
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[pam_yubico.c:parse_cfg(738)] yubi_attr_prefix=(null)
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[pam_yubico.c:parse_cfg(739)] url=(null)
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[pam_yubico.c:parse_cfg(740)] capath=(null)
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[pam_yubico.c:parse_cfg(741)] token_id_length=12
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[pam_yubico.c:parse_cfg(742)] mode=chresp
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[pam_yubico.c:parse_cfg(743)] chalresp_path=(null)
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[pam_yubico.c:pam_sm_authenticate(775)] get user returned: jas
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[pam_yubico.c:do_challenge_response(493)] Loading challenge from file /home/jas/.yubico/challenge-1077187
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[util.c:load_chalresp_state(269)] Challenge: 23001a190724abf46c8022b008ccb65673dd634ecb150613771ec87f37850284d80dd5f8c8e56affb6da2e952b16682160e7f3ac4f816b64126bd9556e5be1, response: 63d4a679ed15335ffd4253e7609963bcdb0834d4, slot: 2
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[pam_yubico.c:do_challenge_response(566)] Got the expected response, generating new challenge (63 bytes).
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[pam_yubico.c:do_challenge_response(629)] Challenge-response success!
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----
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and if there is no YubiKey in the machine it will look like this:
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----
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[pam_yubico.c:parse_cfg(721)] called.
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[pam_yubico.c:parse_cfg(722)] flags 32768 argc 2
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[pam_yubico.c:parse_cfg(724)] argv[0]=mode=challenge-response
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[pam_yubico.c:parse_cfg(724)] argv[1]=debug
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[pam_yubico.c:parse_cfg(725)] id=-1
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[pam_yubico.c:parse_cfg(726)] key=(null)
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[pam_yubico.c:parse_cfg(727)] debug=1
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[pam_yubico.c:parse_cfg(728)] alwaysok=0
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[pam_yubico.c:parse_cfg(729)] verbose_otp=0
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[pam_yubico.c:parse_cfg(730)] try_first_pass=0
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[pam_yubico.c:parse_cfg(731)] use_first_pass=0
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[pam_yubico.c:parse_cfg(732)] authfile=(null)
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[pam_yubico.c:parse_cfg(733)] ldapserver=(null)
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[pam_yubico.c:parse_cfg(734)] ldap_uri=(null)
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[pam_yubico.c:parse_cfg(735)] ldapdn=(null)
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[pam_yubico.c:parse_cfg(736)] user_attr=(null)
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[pam_yubico.c:parse_cfg(737)] yubi_attr=(null)
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[pam_yubico.c:parse_cfg(738)] yubi_attr_prefix=(null)
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[pam_yubico.c:parse_cfg(739)] url=(null)
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[pam_yubico.c:parse_cfg(740)] capath=(null)
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[pam_yubico.c:parse_cfg(741)] token_id_length=12
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[pam_yubico.c:parse_cfg(742)] mode=chresp
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[pam_yubico.c:parse_cfg(743)] chalresp_path=(null)
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[pam_yubico.c:pam_sm_authenticate(775)] get user returned: jas
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[pam_yubico.c:do_challenge_response(478)] Failed initializing YubiKey
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[pam_yubico.c:do_challenge_response(640)] YubiKey core error: no YubiKey present
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----
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