decrypt.c

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/**
 * $Id: 3fd970ccc54d884a5eba35dd6c1ef33eed663d40 $
 * @file decrypt.c
 * @brief Authentication for yubikey OTP tokens using the yubikey library.
 *
 * @author Arran Cudbard-Bell (a.cudbardb@networkradius.com)
 * @copyright 2013 The FreeRADIUS server project
 * @copyright 2013 Network RADIUS (legal@networkradius.com)
 */
#include "rlm_yubikey.h"
 
#ifdef HAVE_YUBIKEY
 
/** Decrypt a Yubikey OTP AES block
 *
 * @param[out] p_result         The result of attempt to decrypt the token.
 * @param[in] mctx              call data.
 * @param[in] request           The current request.
 * @param[in] passcode          string to decrypt.
 */
unlang_action_t rlm_yubikey_decrypt(rlm_rcode_t *p_result, module_ctx_t const *mctx, request_t *request, char const *passcode)
{
        rlm_yubikey_t const *inst = talloc_get_type_abort(mctx->mi->data, rlm_yubikey_t);
        uint32_t counter, timestamp;
        yubikey_token_st token;
 
        fr_pair_t *key, *vp;
 
        key = fr_pair_find_by_da_nested(&request->control_pairs, NULL, attr_yubikey_key);
        if (!key) {
                REDEBUG("Yubikey-Key attribute not found in control list, can't decrypt OTP data");
                RETURN_MODULE_INVALID;
        }
 
        if (key->vp_length != YUBIKEY_KEY_SIZE) {
                REDEBUG("Yubikey-Key length incorrect, expected %u got %zu", YUBIKEY_KEY_SIZE, key->vp_length);
                RETURN_MODULE_INVALID;
        }
 
        yubikey_parse((uint8_t const *) passcode + inst->id_len, key->vp_octets, &token);
 
        /*
         *      Apparently this just uses byte offsets...
         */
        if (!yubikey_crc_ok_p((uint8_t *) &token)) {
                REDEBUG("Decrypting OTP token data failed, rejecting");
                RETURN_MODULE_REJECT;
        }
 
        RDEBUG2("Token data decrypted successfully");
 
        counter = (yubikey_counter(token.ctr) << 8) | token.use;
        timestamp = (token.tstph << 16) | token.tstpl;
 
        RDEBUG2("Private ID        : %pH", fr_box_octets(token.uid, YUBIKEY_UID_SIZE));
        RDEBUG2("Session counter   : %u", counter);
 
        RDEBUG2("Token timestamp   : %u", timestamp);
 
        RDEBUG2("Random data       : %u", token.rnd);
        RDEBUG2("CRC data          : 0x%x", token.crc);
 
        /*
         *      Private ID used for validation purposes
         */
        MEM(pair_update_request(&vp, attr_yubikey_private_id) >= 0);
        fr_pair_value_memdup(vp, token.uid, YUBIKEY_UID_SIZE, true);
 
        /*
         *      Token timestamp
         */
        MEM(pair_update_request(&vp, attr_yubikey_timestamp) >= 0);
        vp->vp_uint32 = timestamp;
 
        /*
         *      Token random
         */
        MEM(pair_update_request(&vp, attr_yubikey_random) >= 0);
        vp->vp_uint32 = token.rnd;
 
        /*
         *      Combine the two counter fields together so we can do
         *      replay attack checks.
         */
        MEM(pair_update_request(&vp, attr_yubikey_counter) >= 0);
        vp->vp_uint32 = counter;
 
        /*
         *      Now we check for replay attacks
         */
        vp = fr_pair_find_by_da_nested(&request->control_pairs, NULL, attr_yubikey_counter);
        if (!vp) {
                RWDEBUG("Yubikey-Counter not found in control list, skipping replay attack checks");
                RETURN_MODULE_OK;
        }
 
        if (counter <= vp->vp_uint32) {
                REDEBUG("Replay attack detected! Counter value %u, is lt or eq to last known counter value %u",
                        counter, vp->vp_uint32);
                RETURN_MODULE_REJECT;
        }
 
        RETURN_MODULE_OK;
}
#endif