EAP-TLS authentication support for PPP
======================================

1. Intro

    The Extensible Authentication Protocol (EAP; RFC 3748) is a
    security protocol that can be used with PPP.  It provides a means
    to plug in multiple optional authentication methods.

    Transport Level Security (TLS; RFC 5216) provides for mutual 
    authentication, integrity-protected ciphersuite negotiation and 
    key exchange between two endpoints.  It also provides for optional
    MPPE encryption.

    EAP-TLS (RFC 2716) incapsulates the TLS messages in EAP packets,
    allowing TLS mutual authentication to be used as a generic EAP
    mechanism. It also provides optional encryption using the MPPE
    protocol.

    EAP-TLS support is included in pppd, and is enabled or disabled
    at configure time by using the --enable-eaptls and --disable-eaptls
    arguments to ./configure.

    This authentication method can be used in both client and server mode.

2. Building

    To build pppd with EAP-TLS support, OpenSSL (http://www.openssl.org)
    is required. Any version from 0.9.7 should work.
    
    Configure, compile, and install as usual. 

3. Configuration

    On the client side there are two ways to configure EAP-TLS:

    1. supply the appropriate 'ca', 'cert' and 'key' command-line parameters

    2. edit the /etc/ppp/eaptls-client file.
    Insert a line for each system with which you use EAP-TLS.
    The line is composed of this fields separated by tab:

      - Client name 
        The name used by the client for authentication, can be *
      - Server name
        The name of the server, can be *
      - Client certificate file 
        The file containing the certificate chain for the 
        client in PEM format
      - Server certificate file
        If you want to specify the certificate that the 
        server is allowed to use, put the certificate file name.
        Else put a dash '-'.
      - CA certificate file
        The file containing the trusted CA certificates in PEM
        format.
      - Client private key file
        The file containing the client private key in PEM format.


    On the server side edit the /etc/ppp/eaptls-server file.
    Insert a line for each system with which you use EAP-TLS.
    The line is composed of this fields separated by tab:

      - Client name
        The name used by the client for authentication, can be *
      - Server name
        The name of the server, can be *
      - Client certificate file
        If you want to specify the certificate that the
        client is allowed to use, put the certificate file name.
        Else put a dash '-'.
      - Server certificate file
        The file containing the certificate chain for the
        server in PEM format
      - CA certificate file
        The file containing the trusted CA certificates in PEM format.
      - Client private key file
        The file containing the server private key in PEM format.
      - addresses
        A list of IP addresses the client is allowed to use.


    OpenSSL engine support is included starting with v0.95 of this patch. 
    Currently the only engine tested is the 'pkcs11' engine (hardware token
    support). To use the 'pksc11' engine:
      - Use a special private key fileiname in the /etc/ppp/eaptls-client file:
          <engine>:<identifier>
        e.g.
          pkcs11:123456

      - The certificate can also be loaded from the 'pkcs11' engine using
        a special client certificate filename in the /etc/ppp/eaptls-client file:
          <engine>:<identifier>
        e.g.
          pkcs11:123456

      - Create an /etc/ppp/openssl.cnf file to load the right OpenSSL engine prior
        to starting 'pppd'. A sample openssl.cnf file is

        openssl_conf = openssl_def

        [ openssl_def ]
        engines = engine_section

        [ engine_section ]
        pkcs11 = pkcs11_section

        [ pkcs11_section ]
        engine_id = pkcs11
        dynamic_path = /usr/lib64/openssl/engines/engine_pkcs11.so
        MODULE_PATH = /usr/lib64/libeTPkcs11.so
        init = 0

      - There are two ways to specify a password/PIN for the PKCS11 engine:
          - inside the openssl.cnf file using
              PIN = your-secret-pin
            Note The keyword 'PIN' is case sensitive!
          - Using the 'password' in the ppp options file.
        From v0.97 of the eap-tls patch the password can also be supplied
        using the appropriate 'eaptls_passwd_hook' (see plugins/passprompt.c
        for an example).


4. Options

    These pppd options are available:

      ca <ca-file>
        Use the CA public certificate found in <ca-file> in PEM format
      capath <directory>
        Use the directory <directory> as the CA public certificate directory
      cert <cert-file>
        Use the client public certificate found in <cert-file> in PEM format
        or in engine:engine_id format
      key <key-file>
        Use the client private key found in <key-file> in PEM format
        or in engine:engine_id format
      pkcs12 <pkcs12-file>
        Use a pkcs12 envelope as a substitute for cert and key. A password may be
        required to use this file. 
      crl <crl-file>
        Use the Certificate Revocation List (CRL) file <crl-file> in PEM format.
      crl-dir <dir>
        Use CRL files from directory <dir>. It contains CRL files in PEM
        format and each file contains a CRL. The files are looked up 
        by the issuer name hash value. Use the c_rehash utility 
        to create necessary links.
      need-peer-eap
        If the peer doesn't ask us to authenticate or doesn't use eap
        to authenticate us, disconnect.
      max-tls-version <1.0|1.1|1.2 (default)|1.3>
        Specify the maximum TLS protocol version to negotiate with peers. Defaults
        to TLSv1.2 as the TLSv1.3 code is experimental.
      tls-verify-key-usage
        Validate certificate purpose and extended key usage
      tls-verify-method <none|subject|name|suffix>
        Compare the remotename against the subject, certificate name, or
        match by suffix. Default is 'name'.

    Note: 
      password-encrypted certificates can be used as of v0.94 of this 
      patch. The password for the eap-tls.key file is specified using 
      the regular
          password ....
      statement in the ppp options file, or by using the appropriate
      plugin which supplies a 'eaptls_passwd_hook' routine.

5. Connecting

    If you're setting up a pppd server, edit the EAP-TLS configuration file 
    as written above and then run pppd with the 'auth' option to authenticate
    the client. The EAP-TLS method will be used if the other eap methods can't
    be used (no secrets).

    If you're setting up a client, edit the configuration file and then run
    pppd with 'remotename' option to specify the server name. Add the 
    'need-peer-eap' option if you want to be sure the peer ask you to
    authenticate (and to use eap) and to disconnect if it doesn't.

6. Example

    The following example can be used to connect a Linux client with the 'pptp'
    package to a Linux server running the 'pptpd' (PoPToP) package. The server
    was configured with a certificate with name (CN) 'pptp-server', the client
    was configured with a certificate with name (CN) 'pptp-client', both 
    signed by the same Certificate Authority (CA).

    Server side:
      - /etc/pptpd.conf file:
          option /etc/ppp/options-pptpd-eaptls
          localip 172.16.1.1
          remoteip 172.16.1.10-20 
      - /etc/ppp/options-pptpd-eaptls file:
          name pptp-server
          lock 
          mtu 1500 
          mru 1450
          auth 
          lcp-echo-failure 3 
          lcp-echo-interval 5 
          nodeflate 
          nobsdcomp
          nopredictor1
          nopcomp
          noaccomp
          
          require-eap
          require-mppe-128
          
          crl /home/janjust/ppp/keys/crl.pem
          
          debug
          logfile /tmp/pppd.log

      - /etc/ppp/eaptls-server file:
           * pptp-server - /etc/ppp/pptp-server.crt /etc/ppp/ca.crt /etc/ppp/pptp-server.key *

      - On the server, run 
          pptdp --conf /etc/pptpd.conf
       
    Client side:
      - Run
          pppd noauth require-eap require-mppe-128 \
            ipcp-accept-local ipcp-accept-remote noipdefault \
            cert  /etc/ppp/keys/pptp-client.crt \
            key   /etc/ppp/keys/pptp-client.key \
            ca    /etc/ppp/keys/ca.crt \
            name pptp-client remotename pptp-server \
            debug logfile /tmp/pppd.log
            pty "pptp pptp-server.example.com --nolaunchpppd"

    Check /var/log/messages and the files /tmp/pppd.log on both sides for debugging info.

7. Notes

    This is experimental code.
    Send suggestions and comments to Jan Just Keijser <janjust@nikhef.nl>

