/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */

/* kdc/kdc_preauth_ec.c - Encrypted challenge kdcpreauth module */

/*

 * Copyright (C) 2009 by the Massachusetts Institute of Technology.

 * All rights reserved.

 *

 * Export of this software from the United States of America may

 *   require a specific license from the United States Government.

 *   It is the responsibility of any person or organization contemplating

 *   export to obtain such a license before exporting.

 *

 * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and

 * distribute this software and its documentation for any purpose and

 * without fee is hereby granted, provided that the above copyright

 * notice appear in all copies and that both that copyright notice and

 * this permission notice appear in supporting documentation, and that

 * the name of M.I.T. not be used in advertising or publicity pertaining

 * to distribution of the software without specific, written prior

 * permission.  Furthermore if you modify this software you must label

 * your software as modified software and not distribute it in such a

 * fashion that it might be confused with the original M.I.T. software.

 * M.I.T. makes no representations about the suitability of

 * this software for any purpose.  It is provided "as is" without express

 * or implied warranty.

 */

/*

 * Implement Encrypted Challenge fast factor from

 * draft-ietf-krb-wg-preauth-framework

 */

#include <k5-int.h>

#include <krb5/kdcpreauth_plugin.h>

#include "kdc_util.h"

static void

ec_edata(krb5_context context, krb5_kdc_req *request,

         krb5_kdcpreauth_callbacks cb, krb5_kdcpreauth_rock rock,

         krb5_kdcpreauth_moddata moddata, krb5_preauthtype pa_type,

         krb5_kdcpreauth_edata_respond_fn respond, void *arg)

{

    krb5_keyblock *armor_key = cb->fast_armor(context, rock);

    /* Encrypted challenge only works with FAST, and requires a client key. */

    if (armor_key == NULL || !cb->have_client_keys(context, rock))

        (*respond)(arg, ENOENT, NULL);

    else

        (*respond)(arg, 0, NULL);

}

static void

ec_verify(krb5_context context, krb5_data *req_pkt, krb5_kdc_req *request,

          krb5_enc_tkt_part *enc_tkt_reply, krb5_pa_data *data,

          krb5_kdcpreauth_callbacks cb, krb5_kdcpreauth_rock rock,

          krb5_kdcpreauth_moddata moddata,

          krb5_kdcpreauth_verify_respond_fn respond, void *arg)

{

    krb5_error_code retval = 0;

    krb5_enc_data *enc = NULL;

    krb5_data scratch, plain;

    krb5_keyblock *armor_key = cb->fast_armor(context, rock);

    krb5_pa_enc_ts *ts = NULL;

    krb5_keyblock *client_keys = NULL;

    krb5_keyblock *challenge_key = NULL;

    krb5_keyblock *kdc_challenge_key;

    krb5_kdcpreauth_modreq modreq = NULL;

    int i = 0;

    char *ai = NULL, *realmstr = NULL;

    krb5_data realm = request->server->realm;

    plain.data = NULL;

    if (armor_key == NULL) {

        retval = ENOENT;

        k5_setmsg(context, ENOENT,

                  _("Encrypted Challenge used outside of FAST tunnel"));

    }

    scratch.data = (char *) data->contents;

    scratch.length = data->length;

    if (retval == 0)

        retval = decode_krb5_enc_data(&scratch, &enc;;

    if (retval == 0) {

        plain.data =  malloc(enc->ciphertext.length);

        plain.length = enc->ciphertext.length;

        if (plain.data == NULL)

            retval = ENOMEM;

    }

    /* Check for a configured FAST ec auth indicator. */

    realmstr = k5memdup0(realm.data, realm.length, &retval);

    if (realmstr != NULL)

        retval = profile_get_string(context->profile, KRB5_CONF_REALMS,

                                    realmstr,

                                    KRB5_CONF_ENCRYPTED_CHALLENGE_INDICATOR,

                                    NULL, &ai;;

    if (retval == 0)

        retval = cb->client_keys(context, rock, &client_keys);

    if (retval == 0) {

        for (i = 0; client_keys[i].enctype&& (retval == 0); i++ ) {

            retval = krb5_c_fx_cf2_simple(context,

                                          armor_key, "clientchallengearmor",

                                          &client_keys[i], "challengelongterm",

                                          &challenge_key);

            if (retval == 0)

                retval  = krb5_c_decrypt(context, challenge_key,

                                         KRB5_KEYUSAGE_ENC_CHALLENGE_CLIENT,

                                         NULL, enc, &plain);

            if (challenge_key)

                krb5_free_keyblock(context, challenge_key);

            challenge_key = NULL;

            if (retval == 0)

                break;

            /*We failed to decrypt. Try next key*/

            retval = 0;

        }

        if (client_keys[i].enctype == 0) {

            retval = KRB5KDC_ERR_PREAUTH_FAILED;

            k5_setmsg(context, retval,

                      _("Incorrect password in encrypted challenge"));

        }

    }

    if (retval == 0)

        retval = decode_krb5_pa_enc_ts(&plain, &ts);

    if (retval == 0)

        retval = krb5_check_clockskew(context, ts->patimestamp);

    if (retval == 0) {

        enc_tkt_reply->flags |= TKT_FLG_PRE_AUTH;

        /*

         * If this fails, we won't generate a reply to the client.  That may

         * cause the client to fail, but at this point the KDC has considered

         * this a success, so the return value is ignored.

         */

        if (krb5_c_fx_cf2_simple(context, armor_key, "kdcchallengearmor",

                                 &client_keys[i], "challengelongterm",

                                 &kdc_challenge_key) == 0) {

            modreq = (krb5_kdcpreauth_modreq)kdc_challenge_key;

            if (ai != NULL)

                cb->add_auth_indicator(context, rock, ai);

        }

    }

    cb->free_keys(context, rock, client_keys);

    if (plain.data)

        free(plain.data);

    if (enc)

        krb5_free_enc_data(context, enc);

    if (ts)

        krb5_free_pa_enc_ts(context, ts);

    free(realmstr);

    free(ai);

    (*respond)(arg, retval, modreq, NULL, NULL);

}

static krb5_error_code

ec_return(krb5_context context, krb5_pa_data *padata, krb5_data *req_pkt,

          krb5_kdc_req *request, krb5_kdc_rep *reply,

          krb5_keyblock *encrypting_key, krb5_pa_data **send_pa,

          krb5_kdcpreauth_callbacks cb, krb5_kdcpreauth_rock rock,

          krb5_kdcpreauth_moddata moddata, krb5_kdcpreauth_modreq modreq)

{

    krb5_error_code retval = 0;

    krb5_keyblock *challenge_key = (krb5_keyblock *)modreq;

    krb5_pa_enc_ts ts;

    krb5_data *plain = NULL;

    krb5_enc_data enc;

    krb5_data *encoded = NULL;

    krb5_pa_data *pa = NULL;

    if (challenge_key == NULL)

        return 0;

    enc.ciphertext.data = NULL; /* In case of error pass through */

    retval = krb5_us_timeofday(context, &ts.patimestamp, &ts.pausec);

    if (retval == 0)

        retval = encode_krb5_pa_enc_ts(&ts, &plain);

    if (retval == 0)

        retval = krb5_encrypt_helper(context, challenge_key,

                                     KRB5_KEYUSAGE_ENC_CHALLENGE_KDC,

                                     plain, &enc;;

    if (retval == 0)

        retval = encode_krb5_enc_data(&enc, &encoded);

    if (retval == 0) {

        pa = calloc(1, sizeof(krb5_pa_data));

        if (pa == NULL)

            retval = ENOMEM;

    }

    if (retval == 0) {

        pa->pa_type = KRB5_PADATA_ENCRYPTED_CHALLENGE;

        pa->contents = (unsigned char *) encoded->data;

        pa->length = encoded->length;

        encoded->data = NULL;

        *send_pa = pa;

        pa = NULL;

    }

    if (challenge_key)

        krb5_free_keyblock(context, challenge_key);

    if (encoded)

        krb5_free_data(context, encoded);

    if (plain)

        krb5_free_data(context, plain);

    if (enc.ciphertext.data)

        krb5_free_data_contents(context, &enc.ciphertext);

    return retval;

}

static krb5_preauthtype ec_types[] = {

    KRB5_PADATA_ENCRYPTED_CHALLENGE, 0};

krb5_error_code

kdcpreauth_encrypted_challenge_initvt(krb5_context context, int maj_ver,

                                      int min_ver, krb5_plugin_vtable vtable)

{

    krb5_kdcpreauth_vtable vt;

    if (maj_ver != 1)

        return KRB5_PLUGIN_VER_NOTSUPP;

    vt = (krb5_kdcpreauth_vtable)vtable;

    vt->name = "encrypted_challenge";

    vt->pa_type_list = ec_types;

    vt->edata = ec_edata;

    vt->verify = ec_verify;

    vt->return_padata = ec_return;

    return 0;

}