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diff --git a/src/libdnssec/nsec.h b/src/libdnssec/nsec.h
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+/*  Copyright (C) 2020 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/*!
+ * \file
+ *
+ * \addtogroup nsec
+ *
+ * \brief NSEC bitmap and NSEC3 hash computation API.
+ *
+ * The module provides interface for computation of NSEC3 hashes and for
+ * construction of bit maps used in NSEC and NSEC3 records.
+ *
+ * @{
+ */
+
+#pragma once
+
+#include <stddef.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+#include <libdnssec/binary.h>
+
+/*!
+ * DNSSEC NSEC3 algorithm numbers.
+ */
+typedef enum dnssec_nsec_algorithm {
+	DNSSEC_NSEC3_ALGORITHM_UNKNOWN = 0,
+	DNSSEC_NSEC3_ALGORITHM_SHA1 = 1,
+} dnssec_nsec3_algorithm_t;
+
+/*!
+ * DNSSEC NSEC3 parameters.
+ */
+typedef struct dnssec_nsec3_params {
+	dnssec_nsec3_algorithm_t algorithm; /*!< NSEC3 algorithm. */
+	uint8_t flags;                      /*!< NSEC3 flags. */
+	uint16_t iterations;                /*!< NSEC3 iterations count. */
+	dnssec_binary_t salt;               /*!< NSEC3 salt. */
+} dnssec_nsec3_params_t;
+
+/*!
+ * Free NSEC3 parameters.
+ */
+void dnssec_nsec3_params_free(dnssec_nsec3_params_t *params);
+
+/*!
+ * Parse NSEC3 parameters from NSEC3PARAM RDATA.
+ *
+ * \param params  Output parameters.
+ * \param rdata   NSEC3PARAM RDATA.
+ *
+ * \return Error code, DNSSEC_EOK if successful.
+ */
+int dnssec_nsec3_params_from_rdata(dnssec_nsec3_params_t *params,
+				   const dnssec_binary_t *rdata);
+
+/*!
+ * Check if NSEC3 parameters match.
+ *
+ * \param params1  NSEC3 parameters 1.
+ * \param params2  NSEC3 parameters 2.
+ *
+ * \return True if match or if both NULL.
+ */
+bool dnssec_nsec3_params_match(const dnssec_nsec3_params_t *params1,
+			       const dnssec_nsec3_params_t *params2);
+
+/*!
+ * Check whether a given NSEC bitmap contains a given RR type.
+ *
+ * \param bitmap  Bitmap of an NSEC record.
+ * \param size    Size of the bitmap.
+ * \param type    RR type to check for.
+ *
+ * \return true if bitmap contains type, false otherwise.
+ */
+bool dnssec_nsec_bitmap_contains(const uint8_t *bitmap, uint16_t size, uint16_t type);
+
+/*!
+ * Compute NSEC3 hash for given data.
+ *
+ * \todo Input data must be converted to lowercase!
+ *
+ * \param[in]  data    Data to be hashed (usually domain name).
+ * \param[in]  params  NSEC3 parameters.
+ * \param[out] hash    Computed hash (will be allocated or resized).
+ *
+ * \return Error code, DNSSEC_EOK if successful.
+ */
+int dnssec_nsec3_hash(const dnssec_binary_t *data,
+		      const dnssec_nsec3_params_t *params,
+		      dnssec_binary_t *hash);
+
+/*!
+ * Get length of raw NSEC3 hash for a given algorithm.
+ *
+ * \param algorithm  NSEC3 algorithm number.
+ *
+ * \return Length of raw NSEC3 hash, zero on error.
+ */
+size_t dnssec_nsec3_hash_length(dnssec_nsec3_algorithm_t algorithm);
+
+struct dnssec_nsec_bitmap;
+
+/*!
+ * Context for encoding of RR types bitmap used in NSEC/NSEC3.
+ */
+typedef struct dnssec_nsec_bitmap dnssec_nsec_bitmap_t;
+
+/*!
+ * Allocate new bit map encoding context.
+ */
+dnssec_nsec_bitmap_t *dnssec_nsec_bitmap_new(void);
+
+/*!
+ * Clear existing bit map encoding context.
+ */
+void dnssec_nsec_bitmap_clear(dnssec_nsec_bitmap_t *bitmap);
+
+/*!
+ * Free bit map encoding context.
+ */
+void dnssec_nsec_bitmap_free(dnssec_nsec_bitmap_t *bitmap);
+
+/*!
+ * Add one RR type into the bitmap.
+ */
+void dnssec_nsec_bitmap_add(dnssec_nsec_bitmap_t *bitmap, uint16_t type);
+
+/*!
+ * Compute the size of the encoded bitmap.
+ */
+size_t dnssec_nsec_bitmap_size(const dnssec_nsec_bitmap_t *bitmap);
+
+/*!
+ * Write encoded bitmap into the given buffer.
+ */
+void dnssec_nsec_bitmap_write(const dnssec_nsec_bitmap_t *bitmap, uint8_t *output);
+
+/*! @} */