X-Git-Url: http://www.average.org/gitweb/?p=pam_pcsc_cr.git;a=blobdiff_plain;f=README;fp=README;h=0000000000000000000000000000000000000000;hp=af0bd7552d3f4036494ee582ca98e1074fc9253a;hb=288c17d345dfd026fb9d71976275cdabdbeeaf88;hpb=bcae8a6776e8824e347752d8dc71492adef6aa57 diff --git a/README b/README deleted file mode 100644 index af0bd75..0000000 --- a/README +++ /dev/null @@ -1,114 +0,0 @@ -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= template used to find the file. - backend:key=val backend options. - -