11 files changed, 788 insertions, 0 deletions

diff --git a/lib/cookies/alg_containers.c b/lib/cookies/alg_containers.c
new file mode 100644
index 0000000..491859b
--- /dev/null
+++ b/lib/cookies/alg_containers.c
@@ -0,0 +1,60 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include <assert.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include <libknot/cookies/alg-fnv64.h>
+
+#include "lib/cookies/alg_containers.h"
+#include "lib/cookies/alg_sha.h"
+
+const struct knot_cc_alg *kr_cc_alg_get(int id)
+{
+	/*
+	 * Client algorithm identifiers are used to index this array of
+	 * pointers.
+	 */
+	static const struct knot_cc_alg *const cc_algs[] = {
+		/* 0 */ &knot_cc_alg_fnv64,
+		/* 1 */ &knot_cc_alg_hmac_sha256_64
+	};
+
+	if (id >= 0 && id < 2) {
+		return cc_algs[id];
+	}
+
+	return NULL;
+}
+
+const knot_lookup_t kr_cc_alg_names[] = {
+	{ 0, "FNV-64" },
+	{ 1, "HMAC-SHA256-64" },
+	{ -1, NULL }
+};
+
+const struct knot_sc_alg *kr_sc_alg_get(int id)
+{
+	/*
+	 * Server algorithm identifiers are used to index this array of
+	 * pointers.
+	 */
+	static const struct knot_sc_alg *const sc_algs[] = {
+		/* 0 */ &knot_sc_alg_fnv64,
+		/* 1 */ &knot_sc_alg_hmac_sha256_64
+	};
+
+	if (id >= 0 && id < 2) {
+		return sc_algs[id];
+	}
+
+	return NULL;
+}
+
+const knot_lookup_t kr_sc_alg_names[] = {
+	{ 0, "FNV-64" },
+	{ 1, "HMAC-SHA256-64" },
+	{ -1, NULL }
+};
diff --git a/lib/cookies/alg_containers.h b/lib/cookies/alg_containers.h
new file mode 100644
index 0000000..3b50cca
--- /dev/null
+++ b/lib/cookies/alg_containers.h
@@ -0,0 +1,37 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include <libknot/cookies/client.h>
+#include <libknot/cookies/server.h>
+#include <libknot/lookup.h>
+
+#include "lib/defines.h"
+
+/**
+ * @brief Returns pointer to client cookie algorithm.
+ *
+ * @param id algorithm identifier as defined by lookup table
+ * @return   pointer to algorithm structure with given id or NULL on error
+ */
+KR_EXPORT
+const struct knot_cc_alg *kr_cc_alg_get(int id);
+
+/** Binds client algorithm identifiers onto names. */
+KR_EXPORT
+extern const knot_lookup_t kr_cc_alg_names[];
+
+/**
+ * @brief Returns pointer to server cookie algorithm.
+ *
+ * @param id algorithm identifier as defined by lookup table
+ * @return   pointer to algorithm structure with given id or NULL on error
+ */
+KR_EXPORT
+const struct knot_sc_alg *kr_sc_alg_get(int id);
+
+/** Binds server algorithm identifiers onto names. */
+KR_EXPORT
+extern const knot_lookup_t kr_sc_alg_names[];
diff --git a/lib/cookies/alg_sha.c b/lib/cookies/alg_sha.c
new file mode 100644
index 0000000..37eafbc
--- /dev/null
+++ b/lib/cookies/alg_sha.c
@@ -0,0 +1,110 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include <assert.h>
+#include <nettle/hmac.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include <libknot/errcode.h>
+#include <libknot/rrtype/opt-cookie.h>
+
+#include "lib/cookies/alg_sha.h"
+#include "lib/utils.h"
+
+/**
+ * @brief Update hash value.
+ *
+ * @param ctx HMAC-SHA256 context to be updated.
+ * @param sa  Socket address.
+ */
+static inline void update_hash(struct hmac_sha256_ctx *ctx,
+                               const struct sockaddr *sa)
+{
+	assert(ctx && sa);
+
+	int addr_len = kr_inaddr_len(sa);
+	const uint8_t *addr = (uint8_t *)kr_inaddr(sa);
+
+	if (addr && addr_len > 0) {
+		hmac_sha256_update(ctx, addr_len, addr);
+	}
+}
+
+/**
+ * @brief Compute client cookie using HMAC-SHA256-64.
+ * @note At least one of the arguments must be non-null.
+ * @param input  input parameters
+ * @param cc_out buffer for computed client cookie
+ * @param cc_len buffer size
+ * @return Non-zero size of written data on success, 0 in case of a failure.
+ */
+static uint16_t cc_gen_hmac_sha256_64(const struct knot_cc_input *input,
+                                      uint8_t *cc_out, uint16_t cc_len)
+{
+	if (!knot_cc_input_is_valid(input) ||
+	    !cc_out || cc_len < KNOT_OPT_COOKIE_CLNT) {
+		return 0;
+	}
+
+	struct hmac_sha256_ctx ctx;
+	hmac_sha256_set_key(&ctx, input->secret_len, input->secret_data);
+
+	if (input->clnt_sockaddr) {
+		update_hash(&ctx, input->clnt_sockaddr);
+	}
+
+	if (input->srvr_sockaddr) {
+		update_hash(&ctx, input->srvr_sockaddr);
+	}
+
+	/* KNOT_OPT_COOKIE_CLNT <= SHA256_DIGEST_SIZE */
+
+	hmac_sha256_digest(&ctx, KNOT_OPT_COOKIE_CLNT, cc_out);
+
+	return KNOT_OPT_COOKIE_CLNT;
+}
+
+#define SRVR_HMAC_SHA256_64_HASH_SIZE 8
+
+/**
+ * @brief Compute server cookie hash using HMAC-SHA256-64).
+ * @note Server cookie = nonce | time | HMAC-SHA256-64( server secret, client cookie | nonce| time | client IP )
+ * @param input    data to compute cookie from
+ * @param hash_out hash output buffer
+ * @param hash_len buffer size
+ * @return Non-zero size of written data on success, 0 in case of a failure.
+ */
+static uint16_t sc_gen_hmac_sha256_64(const struct knot_sc_input *input,
+                                      uint8_t *hash_out, uint16_t hash_len)
+{
+	if (!knot_sc_input_is_valid(input) ||
+	    !hash_out || hash_len < SRVR_HMAC_SHA256_64_HASH_SIZE) {
+		return 0;
+	}
+
+	struct hmac_sha256_ctx ctx;
+	hmac_sha256_set_key(&ctx, input->srvr_data->secret_len,
+	                    input->srvr_data->secret_data);
+
+	hmac_sha256_update(&ctx, input->cc_len, input->cc);
+
+	if (input->nonce && input->nonce_len) {
+		hmac_sha256_update(&ctx, input->nonce_len, input->nonce);
+	}
+
+	if (input->srvr_data->clnt_sockaddr) {
+		update_hash(&ctx, input->srvr_data->clnt_sockaddr);
+	}
+
+	/* SRVR_HMAC_SHA256_64_HASH_SIZE < SHA256_DIGEST_SIZE */
+
+	hmac_sha256_digest(&ctx, SRVR_HMAC_SHA256_64_HASH_SIZE, hash_out);
+
+	return SRVR_HMAC_SHA256_64_HASH_SIZE;
+}
+
+const struct knot_cc_alg knot_cc_alg_hmac_sha256_64 = { KNOT_OPT_COOKIE_CLNT, cc_gen_hmac_sha256_64 };
+
+const struct knot_sc_alg knot_sc_alg_hmac_sha256_64 = { SRVR_HMAC_SHA256_64_HASH_SIZE, sc_gen_hmac_sha256_64 };
diff --git a/lib/cookies/alg_sha.h b/lib/cookies/alg_sha.h
new file mode 100644
index 0000000..de7a75a
--- /dev/null
+++ b/lib/cookies/alg_sha.h
@@ -0,0 +1,18 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include <libknot/cookies/client.h>
+#include <libknot/cookies/server.h>
+
+#include "lib/defines.h"
+
+/* These structures are not meant to be part of public interface. */
+
+/** HMAC-SHA256-64 client cookie algorithm. */
+extern const struct knot_cc_alg knot_cc_alg_hmac_sha256_64;
+
+/** HMAC-SHA256-64 server cookie algorithm. */
+extern const struct knot_sc_alg knot_sc_alg_hmac_sha256_64;
diff --git a/lib/cookies/control.h b/lib/cookies/control.h
new file mode 100644
index 0000000..f977c94
--- /dev/null
+++ b/lib/cookies/control.h
@@ -0,0 +1,37 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "lib/defines.h"
+
+/** Holds secret quantity. */
+struct kr_cookie_secret {
+	size_t size; /*!< Secret quantity size. */
+	uint8_t data[]; /*!< Secret quantity data. */
+};
+
+/** Holds settings that have direct influence on cookie values computation. */
+struct kr_cookie_comp {
+	struct kr_cookie_secret *secr; /*!< Secret data. */
+	int alg_id; /*!< Cookie algorithm identifier. */
+};
+
+/** Holds settings that control client/server cookie behaviour. */
+struct kr_cookie_settings {
+	bool enabled; /**< Enable/disables DNS cookies functionality. */
+
+	struct kr_cookie_comp current; /**< Current cookie settings. */
+	struct kr_cookie_comp recent; /**< Recent cookie settings. */
+};
+
+/** DNS cookies controlling structure. */
+struct kr_cookie_ctx {
+	struct kr_cookie_settings clnt; /**< Client settings. */
+	struct kr_cookie_settings srvr; /**< Server settings. */
+};
diff --git a/lib/cookies/helper.c b/lib/cookies/helper.c
new file mode 100644
index 0000000..55c4fbc
--- /dev/null
+++ b/lib/cookies/helper.c
@@ -0,0 +1,284 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include <assert.h>
+#include <libknot/rrtype/opt.h>
+#include <libknot/rrtype/opt-cookie.h>
+
+#include "lib/cookies/helper.h"
+#include "lib/defines.h"
+
+/**
+ * @brief Check whether there is a cached cookie that matches the current
+ *        client cookie.
+ */
+static const uint8_t *peek_and_check_cc(kr_cookie_lru_t *cache, const void *sa,
+                                        const uint8_t *cc, uint16_t cc_len)
+{
+	assert(cache && sa && cc && cc_len);
+
+	const uint8_t *cached_opt = kr_cookie_lru_get(cache, sa);
+	if (!cached_opt) {
+		return NULL;
+	}
+
+	const uint8_t *cached_cc = knot_edns_opt_get_data((uint8_t *) cached_opt);
+
+	if (cc_len == KNOT_OPT_COOKIE_CLNT &&
+	    0 == memcmp(cc, cached_cc, cc_len)) {
+		return cached_opt;
+	}
+
+	return NULL;
+}
+
+/**
+ * @brief Put a client cookie into the RR Set.
+ */
+static int opt_rr_put_cookie(knot_rrset_t *opt_rr, uint8_t *data,
+                             uint16_t data_len, knot_mm_t *mm)
+{
+	assert(opt_rr && data && data_len > 0);
+
+	const uint8_t *cc = NULL, *sc = NULL;
+	uint16_t cc_len = 0, sc_len = 0;
+
+	int ret = knot_edns_opt_cookie_parse(data, data_len, &cc, &cc_len,
+	                                     &sc, &sc_len);
+	if (ret != KNOT_EOK) {
+		return kr_error(EINVAL);
+	}
+	assert(data_len == cc_len + sc_len);
+
+	uint16_t cookies_size = data_len;
+	uint8_t *cookies_data = NULL;
+
+	ret = knot_edns_reserve_unique_option(opt_rr, KNOT_EDNS_OPTION_COOKIE,
+	                                      cookies_size, &cookies_data, mm);
+	if (ret != KNOT_EOK) {
+		return kr_error(EINVAL);
+	}
+	assert(cookies_data != NULL);
+
+	cookies_size = knot_edns_opt_cookie_write(cc, cc_len, sc, sc_len,
+	                                          cookies_data, cookies_size);
+	if (cookies_size == 0) {
+		return kr_error(EINVAL);
+	}
+	assert(cookies_size == data_len);
+
+	return kr_ok();
+}
+
+/**
+ * @brief Puts entire EDNS option into the RR Set.
+ */
+static int opt_rr_put_cookie_opt(knot_rrset_t *opt_rr, uint8_t *option, knot_mm_t *mm)
+{
+	assert(opt_rr && option);
+
+	uint16_t opt_code = knot_edns_opt_get_code(option);
+	if (opt_code != KNOT_EDNS_OPTION_COOKIE) {
+		return kr_error(EINVAL);
+	}
+
+	uint16_t opt_len = knot_edns_opt_get_length(option);
+	uint8_t *opt_data = knot_edns_opt_get_data(option);
+	if (!opt_data || opt_len == 0) {
+		return kr_error(EINVAL);
+	}
+
+	return opt_rr_put_cookie(opt_rr, opt_data, opt_len, mm);
+}
+
+int kr_request_put_cookie(const struct kr_cookie_comp *clnt_comp,
+                          kr_cookie_lru_t *cookie_cache,
+                          const struct sockaddr *clnt_sa,
+                          const struct sockaddr *srvr_sa,
+                          struct kr_request *req)
+{
+	if (!clnt_comp || !req) {
+		return kr_error(EINVAL);
+	}
+
+	if (!req->ctx->opt_rr) {
+		return kr_ok();
+	}
+
+	if (!clnt_comp->secr || (clnt_comp->alg_id < 0) || !cookie_cache) {
+		return kr_error(EINVAL);
+	}
+
+	/*
+	 * Generate client cookie from client address, server address and
+	 * secret quantity.
+	 */
+	struct knot_cc_input input = {
+		.clnt_sockaddr = clnt_sa,
+		.srvr_sockaddr = srvr_sa,
+		.secret_data = clnt_comp->secr->data,
+		.secret_len = clnt_comp->secr->size
+	};
+	uint8_t cc[KNOT_OPT_COOKIE_CLNT];
+	uint16_t cc_len = KNOT_OPT_COOKIE_CLNT;
+	const struct knot_cc_alg *cc_alg = kr_cc_alg_get(clnt_comp->alg_id);
+	if (!cc_alg) {
+		return kr_error(EINVAL);
+	}
+	assert(cc_alg->gen_func);
+	cc_len = cc_alg->gen_func(&input, cc, cc_len);
+	if (cc_len != KNOT_OPT_COOKIE_CLNT) {
+		return kr_error(EINVAL);
+	}
+
+	const uint8_t *cached_cookie = peek_and_check_cc(cookie_cache,
+	                                                 srvr_sa, cc, cc_len);
+
+	/* Add cookie option. */
+	int ret;
+	if (cached_cookie) {
+		ret = opt_rr_put_cookie_opt(req->ctx->opt_rr,
+		                            (uint8_t *)cached_cookie,
+		                            req->ctx->pool);
+	} else {
+		ret = opt_rr_put_cookie(req->ctx->opt_rr, cc, cc_len,
+		                        req->ctx->pool);
+	}
+
+	return ret;
+}
+
+int kr_answer_write_cookie(struct knot_sc_input *sc_input,
+                           const struct kr_nonce_input *nonce,
+                           const struct knot_sc_alg *alg, knot_pkt_t *pkt)
+{
+	if (!sc_input || !sc_input->cc || sc_input->cc_len == 0) {
+		return kr_error(EINVAL);
+	}
+
+	if (!sc_input->srvr_data || !sc_input->srvr_data->clnt_sockaddr ||
+	    !sc_input->srvr_data->secret_data ||
+	    !sc_input->srvr_data->secret_len) {
+		return kr_error(EINVAL);
+	}
+
+	if (!nonce) {
+		return kr_error(EINVAL);
+	}
+
+	if (!alg || !alg->hash_size || !alg->hash_func) {
+		return kr_error(EINVAL);
+	}
+
+	if (!pkt || !pkt->opt_rr) {
+		return kr_error(EINVAL);
+	}
+
+	uint16_t nonce_len = KR_NONCE_LEN;
+	uint16_t hash_len = alg->hash_size;
+
+	/*
+	 * Space for cookie is reserved inside the EDNS OPT RR of
+	 * the answer packet.
+	 */
+	uint8_t *cookie = NULL;
+	uint16_t cookie_len = knot_edns_opt_cookie_data_len(sc_input->cc_len,
+	                                                    nonce_len + hash_len);
+	if (cookie_len == 0) {
+		return kr_error(EINVAL);
+	}
+
+	int ret = knot_edns_reserve_unique_option(pkt->opt_rr,
+	                                          KNOT_EDNS_OPTION_COOKIE,
+	                                          cookie_len, &cookie,
+	                                          &pkt->mm);
+	if (ret != KNOT_EOK) {
+		return kr_error(ENOMEM);
+	}
+	assert(cookie != NULL);
+
+	/*
+	 * Function knot_edns_opt_cookie_data_len() returns the sum of its
+	 * parameters or zero. Anyway, let's check again.
+	 */
+	if (cookie_len < (sc_input->cc_len + nonce_len + hash_len)) {
+		return kr_error(EINVAL);
+	}
+
+	/* Copy client cookie data portion. */
+	memcpy(cookie, sc_input->cc, sc_input->cc_len);
+
+	if (nonce_len) {
+		/* Write nonce data portion. */
+		kr_nonce_write_wire(cookie + sc_input->cc_len, nonce_len,
+		                    nonce);
+		/* Adjust input for written nonce value. */
+		sc_input->nonce = cookie + sc_input->cc_len;
+		sc_input->nonce_len = nonce_len;
+	}
+
+	hash_len = alg->hash_func(sc_input,
+	                          cookie + sc_input->cc_len + nonce_len,
+	                          hash_len);
+	/* Zero nonce values. */
+	sc_input->nonce = NULL;
+	sc_input->nonce_len = 0;
+
+	return (hash_len != 0) ? kr_ok() : kr_error(EINVAL);
+}
+
+int kr_pkt_set_ext_rcode(knot_pkt_t *pkt, uint16_t whole_rcode)
+{
+	/*
+	 * RFC6891 6.1.3 -- extended RCODE forms the upper 8 bits of whole
+	 * 12-bit RCODE (together with the 4 bits of 'normal' RCODE).
+	 *
+	 * | 11 10 09 08 07 06 05 04 | 03 02 01 00 |
+	 * |          12-bit whole RCODE           |
+	 * |   8-bit extended RCODE  | 4-bit RCODE |
+	 */
+
+	if (!pkt || !knot_pkt_has_edns(pkt)) {
+		return kr_error(EINVAL);
+	}
+
+	uint8_t rcode = whole_rcode & 0x0f;
+	uint8_t ext_rcode = whole_rcode >> 4;
+	knot_wire_set_rcode(pkt->wire, rcode);
+	knot_edns_set_ext_rcode(pkt->opt_rr, ext_rcode);
+
+	return kr_ok();
+}
+
+uint8_t *kr_no_question_cookie_query(const knot_pkt_t *pkt)
+{
+	if (!pkt || knot_wire_get_qdcount(pkt->wire) > 0) {
+		return false;
+	}
+
+	if (knot_wire_get_qr(pkt->wire) != 0 || !pkt->opt_rr) {
+		return false;
+	}
+
+	return knot_edns_get_option(pkt->opt_rr, KNOT_EDNS_OPTION_COOKIE);
+}
+
+int kr_parse_cookie_opt(uint8_t *cookie_opt, struct knot_dns_cookies *cookies)
+{
+	if (!cookie_opt || !cookies) {
+		return kr_error(EINVAL);
+	}
+
+	const uint8_t *cookie_data = knot_edns_opt_get_data(cookie_opt);
+	uint16_t cookie_len = knot_edns_opt_get_length(cookie_opt);
+	if (!cookie_data || cookie_len == 0) {
+		return kr_error(EINVAL);
+	}
+
+	int ret =  knot_edns_opt_cookie_parse(cookie_data, cookie_len,
+	                                      &cookies->cc, &cookies->cc_len,
+	                                      &cookies->sc, &cookies->sc_len);
+
+	return (ret == KNOT_EOK) ? kr_ok() : kr_error(EINVAL);
+}
diff --git a/lib/cookies/helper.h b/lib/cookies/helper.h
new file mode 100644
index 0000000..0fee2fc
--- /dev/null
+++ b/lib/cookies/helper.h
@@ -0,0 +1,74 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include <libknot/packet/pkt.h>
+
+#include "lib/cookies/alg_containers.h"
+#include "lib/cookies/control.h"
+#include "lib/cookies/lru_cache.h"
+#include "lib/cookies/nonce.h"
+#include "lib/defines.h"
+#include "lib/resolve.h"
+
+/**
+ * @brief Updates DNS cookie in the request EDNS options.
+ * @note This function must be called before the request packet is finalised.
+ * @param clnt_comp    client cookie control structure
+ * @param cookie_cache cookie cache
+ * @param clnt_sa      client socket address
+ * @param srvr_sa      server socket address
+ * @param req          name resolution request
+ * @return kr_ok() or error code
+ */
+KR_EXPORT
+int kr_request_put_cookie(const struct kr_cookie_comp *clnt_comp,
+                          kr_cookie_lru_t *cookie_cache,
+                          const struct sockaddr *clnt_sa,
+                          const struct sockaddr *srvr_sa,
+                          struct kr_request *req);
+
+/**
+ * @brief Inserts a cookie option into the OPT RR. It does not write any
+ *        wire data.
+ * @note The content of @a sc_input is modified. Any pre-set nonce value is
+ *       ignored. After retuning its nonce value will be null.
+ * @param sc_input  data needed to compute server cookie, nonce is ignored
+ * @param nonce     nonce value that is actually used
+ * @param alg       hash algorithm
+ * @param pkt       DNS response packet
+ */
+KR_EXPORT
+int kr_answer_write_cookie(struct knot_sc_input *sc_input,
+                           const struct kr_nonce_input *nonce,
+                           const struct knot_sc_alg *alg, knot_pkt_t *pkt);
+
+/**
+ * @brief Set RCODE and extended RCODE.
+ * @param pkt DNS packet
+ * @param whole_rcode RCODE value
+ * @return kr_ok() or error code
+ */
+KR_EXPORT
+int kr_pkt_set_ext_rcode(knot_pkt_t *pkt, uint16_t whole_rcode);
+
+/**
+ * @brief Check whether packet is a server cookie request according to
+ *        RFC7873 5.4.
+ * @param pkt Packet to be examined.
+ * @return Pointer to entire cookie option if is a server cookie query, NULL on
+ *         errors or if packet doesn't contain cookies or if QDCOUNT > 0.
+ */
+KR_EXPORT
+uint8_t *kr_no_question_cookie_query(const knot_pkt_t *pkt);
+
+/**
+ * @brief Parse cookies from cookie option.
+ * @param cookie_opt Cookie option.
+ * @param cookies    Cookie structure to be set.
+ * @return kr_ok() on success, error if cookies are malformed.
+ */
+KR_EXPORT
+int kr_parse_cookie_opt(uint8_t *cookie_opt, struct knot_dns_cookies *cookies);
diff --git a/lib/cookies/lru_cache.c b/lib/cookies/lru_cache.c
new file mode 100644
index 0000000..1b629f7
--- /dev/null
+++ b/lib/cookies/lru_cache.c
@@ -0,0 +1,58 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include <libknot/rrtype/opt.h>
+#include <string.h>
+
+#include "lib/cookies/lru_cache.h"
+#include "lib/utils.h"
+
+const uint8_t *kr_cookie_lru_get(kr_cookie_lru_t *cache,
+                                 const struct sockaddr *sa)
+{
+	if (!cache || !sa) {
+		return NULL;
+	}
+
+	int addr_len = kr_inaddr_len(sa);
+	const char *addr = kr_inaddr(sa);
+	if (!addr || addr_len <= 0) {
+		return NULL;
+	}
+
+	struct cookie_opt_data *cached = lru_get_try(cache, addr, addr_len);
+	return cached ? cached->opt_data : NULL;
+}
+
+int kr_cookie_lru_set(kr_cookie_lru_t *cache, const struct sockaddr *sa,
+                      uint8_t *opt)
+{
+	if (!cache || !sa) {
+		return kr_error(EINVAL);
+	}
+
+	if (!opt) {
+		return kr_ok();
+	}
+
+	int addr_len = kr_inaddr_len(sa);
+	const char *addr = kr_inaddr(sa);
+	if (!addr || addr_len <= 0) {
+		return kr_error(EINVAL);
+	}
+
+	uint16_t opt_size = KNOT_EDNS_OPTION_HDRLEN +
+	                    knot_edns_opt_get_length(opt);
+
+	if (opt_size > KR_COOKIE_OPT_MAX_LEN) {
+		return kr_error(EINVAL);
+	}
+
+	struct cookie_opt_data *cached = lru_get_new(cache, addr, addr_len, NULL);
+	if (cached) {
+		memcpy(cached->opt_data, opt, opt_size);
+	}
+
+	return kr_ok();
+}
diff --git a/lib/cookies/lru_cache.h b/lib/cookies/lru_cache.h
new file mode 100644
index 0000000..3594ee1
--- /dev/null
+++ b/lib/cookies/lru_cache.h
@@ -0,0 +1,57 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include <netinet/in.h>
+#include <stdint.h>
+
+#if ENABLE_COOKIES
+#include <libknot/rrtype/opt.h>
+#include <libknot/rrtype/opt-cookie.h>
+#else
+#define KNOT_OPT_COOKIE_CLNT 8
+#define KNOT_OPT_COOKIE_SRVR_MAX 32
+#endif /* ENABLE_COOKIES */
+
+#include "lib/defines.h"
+#include "lib/generic/lru.h"
+
+/** Maximal size of a cookie option. */
+#define KR_COOKIE_OPT_MAX_LEN (KNOT_EDNS_OPTION_HDRLEN + KNOT_OPT_COOKIE_CLNT + KNOT_OPT_COOKIE_SRVR_MAX)
+
+/**
+ * Cookie option entry.
+ */
+struct cookie_opt_data {
+	uint8_t opt_data[KR_COOKIE_OPT_MAX_LEN];
+};
+
+/**
+ * DNS cookies tracking.
+ */
+typedef lru_t(struct cookie_opt_data) kr_cookie_lru_t;
+
+/**
+ * @brief Obtain LRU cache entry.
+ *
+ * @param cache cookie LRU cache
+ * @param sa socket address serving as key
+ * @return pointer to cached option or NULL if not found or error occurred
+ */
+KR_EXPORT
+const uint8_t *kr_cookie_lru_get(kr_cookie_lru_t *cache,
+                                 const struct sockaddr *sa);
+
+/**
+ * @brief Stores cookie option into LRU cache.
+ *
+ * @param cache cookie LRU cache
+ * @param sa socket address serving as key
+ * @param opt cookie option to be stored
+ * @return kr_ok() or error code
+ */
+KR_EXPORT
+int kr_cookie_lru_set(kr_cookie_lru_t *cache, const struct sockaddr *sa,
+                      uint8_t *opt);
diff --git a/lib/cookies/nonce.c b/lib/cookies/nonce.c
new file mode 100644
index 0000000..8e4b754
--- /dev/null
+++ b/lib/cookies/nonce.c
@@ -0,0 +1,22 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include <assert.h>
+
+#include "contrib/wire.h"
+#include "lib/cookies/nonce.h"
+
+uint16_t kr_nonce_write_wire(uint8_t *buf, uint16_t buf_len,
+                             const struct kr_nonce_input *input)
+{
+	if (!buf || buf_len < KR_NONCE_LEN || !input) {
+		return 0;
+	}
+
+	wire_write_u32(buf, input->rand);
+	wire_write_u32(buf + sizeof(uint32_t), input->time);
+	buf_len = 2 * sizeof(uint32_t);
+
+	return buf_len;
+}
diff --git a/lib/cookies/nonce.h b/lib/cookies/nonce.h
new file mode 100644
index 0000000..4d8460f
--- /dev/null
+++ b/lib/cookies/nonce.h
@@ -0,0 +1,31 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include "lib/defines.h"
+
+/* RFC7873 Appendix B.2 mentions an algorithm using two values before the
+ * actual server cookie hash. */
+
+/** Nonce value length. */
+#define KR_NONCE_LEN 8
+
+/** Input data to generate nonce from. */
+struct kr_nonce_input {
+	uint32_t rand; /**< some random value */
+	uint32_t time; /**< time stamp */
+};
+
+/**
+ * @brief Writes server cookie nonce value into given buffer.
+ *
+ * @param buf     buffer to write nonce data in wire format into
+ * @param buf_len buffer size
+ * @param input   data to generate wire data from
+ * @return non-zero size of written data on success, 0 on failure
+ */
+KR_EXPORT
+uint16_t kr_nonce_write_wire(uint8_t *buf, uint16_t buf_len,
+                             const struct kr_nonce_input *input);