+++ /dev/null
-Copyright (c) 2013 Eugene Crosser
-
-This software is provided 'as-is', without any express or implied
-warranty. In no event will the authors be held liable for any damages
-arising from the use of this software.
-
-Permission is granted to anyone to use this software for any purpose,
-including commercial applications, and to alter it and redistribute it
-freely, subject to the following restrictions:
-
- 1. The origin of this software must not be misrepresented; you must
- not claim that you wrote the original software. If you use this
- software in a product, an acknowledgment in the product documentation
- would be appreciated but is not required.
-
- 2. Altered source versions must be plainly marked as such, and must
- not be misrepresented as being the original software.
-
- 3. This notice may not be removed or altered from any source
- distribution.
-
-========================================================================
-
-This package provides a UNIX PAM module and accompanying setup program
-implementing HMAC-SHA1 challenge-response user authentication with
-hardware crypto token supporting PC/SC (Smartcard) interface.
-
-At the time of writing, I know of just one such hardware token, Yubikey
-Neo from Yubico http://www.yubico.com/. Pcsclite infrastructure (i.e.
-library and a daemon) is used to communicate with the token over CCID
-(i.e. PC/SC over USB) or NFC. It means that it works equally well when
-you plug the token in a USB slot and if you put it on an NFC reader.
-
-There are two ways to do challenge-response authentication: with shared
-secret and with pre-produced response. In pre-produced response, the
-host does not need to store the token's HMAC secret; on every session
-conversation with the token is performed twice with different challenges.
-The first response is compared with stored expected response, which is
-then replaced with the second response to be used on the next session.
-The advantage is that the secret is not kept anywhere except the token,
-so it's less chance of compromise. The drawback is that the expected
-response is transferred in cleartext long before being used, and can
-be eavesdropped on and reused in a replay attack. This is of particular
-concern when using NFC. This approach is used by the PAM module provided
-by Yubico.
-
-My module uses the second approach, under which the HMAC secret is
-stored both in the token and on the host. To minimize the danger of
-compromise, the host copy of the shared secret is encrypted by the key
-which is the expected response from the token. In the process of
-authentication, token's response is used to decrypt the secret, then
-this secret is used to compute the next expected token's response, and
-this expected response is used to encrypt the secret again. This next
-expected response is not transferred over the air, and the shared secret
-stays in unencrypted form in RAM (unless paged out) for a very short
-period. The downside is that if the token is used against multiple
-hosts, and one of them leaks the key to an adversary, all hosts are
-compromised. This is not the case with the first approach.
-
-Authentication file, containing nonce, encrypted shared secret,
-encrypted additional payload, and anciliary information, is named
-according to template that can be provided both to PAM module and to the
-setup program (and must be the same, obviously). In the template string,
-character '~' in the first position is substituted with the userid's
-home directory, '~' in a position other than first - with the userid
-itself, and character '?' - with the "tokenid". This latter is just an
-arbitrary string that is not involved in the authentication process.
-But, if the template contains '?' but not '~', login process can start
-without the knowlege of the userid. Userid will be picked from the file
-and injected into the PAM environment, given that tokenid is known from
-the start.
-
-Default template string is "~/.pam_cr/auth", i.e. the file lives in the
-user's home directory, in the subdirectory ".pam_cr".
-
-Authentication file must be initially created by the program
-'pam_cr_setup' included in this package.
-
-usage: pam_cr_setup [options] [username]
- -h - show this help and exit
- -o backend-option - token option "backend:key=val"
- -f template - template for auth state filepath
- -a secret | -A file-with-secret | -A -
- - 40-character hexadecimal secret
- -s token-serial - public I.D. of the token
- -n nonce - initial nonce
- -l payload - keyring unlock password
- -p password - login password
- -v - show returned data
-
-The only backend option existing is "ykneo:slot=1" or "ykneo:slot=2".
-Slot 2 is the default. Secret must be supplied when creating the file,
-and when modifying the file in the absense of the token. Password is
-used to construct the challenge. If not supplied empty string is used.
-The pam module also used empty string when given "noaskpass" argument,
-so this can be used for "one factor" authentication mode with token
-only. Payload is a string that can be optionally injected as the PAM
-authentication token after successful authentication; subsequent PAM
-modules like gnome keyring unlocker module will pick it up. Note that
-this keyring unlocker password may be different from the login
-password, and it is generally a good idea to make it so. The "returned
-data" is the userid as recorded in the file and the aforementioned
-payload string.
-
-PAM module has the following parameters:
- verbose write more errors to syslog.
- noaskpass do not try to ask the user for the challenge
- password, use empty string for the password.
- injectauth inject payload as PAM_AUTHTOK for the benefit
- of subsequent PAM modules.
- path=<string> template used to find the file.
- backend:key=val backend options.
-
-
projects / pam_pcsc_cr.git / blobdiff