1 files changed, 137 insertions, 0 deletions
diff --git a/src/modules/rlm_yubikey/decrypt.c b/src/modules/rlm_yubikey/decrypt.c
new file mode 100644
index 0000000..20b6df8
--- /dev/null
+++ b/src/modules/rlm_yubikey/decrypt.c
@@ -0,0 +1,137 @@
+/**
+ * $Id$
+ * @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 <info@networkradius.com>
+ */
+#include "rlm_yubikey.h"
+
+#ifdef HAVE_YUBIKEY
+/** Decrypt a Yubikey OTP AES block
+ *
+ * @param inst Module configuration.
+ * @param request The current request.
+ * @param passcode string to decrypt.
+ * @return one of the RLM_RCODE_* constants.
+ */
+rlm_rcode_t rlm_yubikey_decrypt(rlm_yubikey_t *inst, REQUEST *request, char const *passcode)
+{
+	uint32_t counter;
+	yubikey_token_st token;
+
+	DICT_ATTR const *da;
+
+	char private_id[(YUBIKEY_UID_SIZE * 2) + 1];
+	VALUE_PAIR *key, *vp;
+
+	da = dict_attrbyname("Yubikey-Key");
+	if (!da) {
+		REDEBUG("Dictionary missing entry for 'Yubikey-Key'");
+		return RLM_MODULE_FAIL;
+	}
+
+	key = fr_pair_find_by_da(request->config, da, TAG_ANY);
+	if (!key) {
+		REDEBUG("Yubikey-Key attribute not found in control list, can't decrypt OTP data");
+		return RLM_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 RLM_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 RLM_MODULE_REJECT;
+	}
+
+	RDEBUG("Token data decrypted successfully");
+
+	if (RDEBUG_ENABLED2) {
+		(void) fr_bin2hex((char *) &private_id, (uint8_t*) &token.uid, YUBIKEY_UID_SIZE);
+		RDEBUG2("Private ID	: 0x%s", private_id);
+		RDEBUG2("Session counter   : %u", yubikey_counter(token.ctr));
+		RDEBUG2("# used in session : %u", token.use);
+		RDEBUG2("Token timestamp    : %u",
+			(token.tstph << 16) | token.tstpl);
+		RDEBUG2("Random data       : %u", token.rnd);
+		RDEBUG2("CRC data          : 0x%x", token.crc);
+	}
+
+	/*
+	 *	Private ID used for validation purposes
+	 */
+	vp = fr_pair_make(request->packet, &request->packet->vps, "Yubikey-Private-ID", NULL, T_OP_SET);
+	if (!vp) {
+		REDEBUG("Failed creating Yubikey-Private-ID");
+
+		return RLM_MODULE_FAIL;
+	}
+	fr_pair_value_memcpy(vp, token.uid, YUBIKEY_UID_SIZE);
+
+	/*
+	 *	Token timestamp
+	 */
+	vp = fr_pair_make(request->packet, &request->packet->vps, "Yubikey-Timestamp", NULL, T_OP_SET);
+	if (!vp) {
+		REDEBUG("Failed creating Yubikey-Timestamp");
+
+		return RLM_MODULE_FAIL;
+	}
+	vp->vp_integer = (token.tstph << 16) | token.tstpl;
+	vp->vp_length = 4;
+
+	/*
+	 *	Token random
+	 */
+	vp = fr_pair_make(request->packet, &request->packet->vps, "Yubikey-Random", NULL, T_OP_SET);
+	if (!vp) {
+		REDEBUG("Failed creating Yubikey-Random");
+
+		return RLM_MODULE_FAIL;
+	}
+	vp->vp_integer = token.rnd;
+	vp->vp_length = 4;
+
+	/*
+	 *	Combine the two counter fields together so we can do
+	 *	replay attack checks.
+	 */
+	counter = (yubikey_counter(token.ctr) << 16) | token.use;
+
+	vp = fr_pair_make(request->packet, &request->packet->vps, "Yubikey-Counter", NULL, T_OP_SET);
+	if (!vp) {
+		REDEBUG("Failed creating Yubikey-Counter");
+
+		return RLM_MODULE_FAIL;
+	}
+	vp->vp_integer = counter;
+	vp->vp_length = 4;
+
+	/*
+	 *	Now we check for replay attacks
+	 */
+	vp = fr_pair_find_by_da(request->config, vp->da, TAG_ANY);
+	if (!vp) {
+		RWDEBUG("Yubikey-Counter not found in control list, skipping replay attack checks");
+		return RLM_MODULE_OK;
+	}
+
+	if (counter <= vp->vp_integer) {
+		REDEBUG("Replay attack detected! Counter value %u, is lt or eq to last known counter value %u",
+			counter, vp->vp_integer);
+		return RLM_MODULE_REJECT;
+	}
+
+	return RLM_MODULE_OK;
+}
+#endif