+++ /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.
-
-
--- /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.
+```
+
+------------------------------------------------------------------------
+
+# Challenge-Response PAM Module for HMAC-SHA1 Hardware Token(s)
+
+This package provides a UNIX
+[PAM](http://en.wikipedia.org/wiki/Pluggable_Authentication_Modules)
+module and accompanying setup program implementing
+[HMAC-SHA1](http://en.wikipedia.org/wiki/HMAC-SHA1) challenge-response
+user authentication with hardware crypto token supporting
+[PC/SC](http://en.wikipedia.org/wiki/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](http://pcsclite.alioth.debian.org/) infrastructure (i.e.
+library and a daemon) is used to communicate with the token over
+[CCID](http://en.wikipedia.org/wiki/Integrated_Circuit_Card_Interface_Device)
+(i.e. PC/SC over USB) or
+[NFC](http://en.wikipedia.org/wiki/Near_field_communication). 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.
+
+## Theory of Challenge-Response Authentication
+
+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 used to decrypt stored encrypted challenge and
+compare it with cleartext challenge. A new challenge is then sent
+to the token, and response is used to encrypt it and store for the
+future authentication 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 response is transferred in cleartext long before
+being used, and can be eavesdropped on and used in a replay attack. This
+is of particular concern when using NFC. This approach is used by the
+[PAM module provided by Yubico](https://github.com/Yubico/yubico-pam).
+
+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 the 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 secret to an adversary, all hosts are
+compromised. This is not the case with the first approach.
+
+## Module Operation
+
+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.
+```
+
+## Getting the Source
+
+[clone](git://git.average.org/git/pam_pcsc_cr.git) or
+[browse](http://www.average.org/gitweb/?p=pam_pcsc_cr.git;a=summary)
+the repo.
+
+## Author
+
+Eugene Crosser \<crosser at average dot org\>
+<http://www.average.org/~crosser/>
+
+---
projects / pam_pcsc_cr.git / commitdiff