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diff --git a/lib/isc/include/isc/hmac.h b/lib/isc/include/isc/hmac.h
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+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at https://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+/*!
+ * \file isc/hmac.h
+ * \brief This is the header for for message authentication code.
+ */
+
+#pragma once
+
+#include <isc/lang.h>
+#include <isc/md.h>
+#include <isc/result.h>
+#include <isc/types.h>
+
+typedef void isc_hmac_t;
+
+/**
+ * isc_hmac:
+ * @type: the digest type
+ * @key: the key
+ * @keylen: the length of the key
+ * @buf: data to hash
+ * @len: length of the data to hash
+ * @digest: the output buffer
+ * @digestlen: in: the length of @digest
+ *             out: the length of the data written to @digest
+ *
+ * This function computes the message authentication code using a digest type
+ * @type with key @key which is @keylen bytes long from data in @buf which is
+ * @len bytes long, and places the output into @digest, which must have space
+ * for the hash function output (use ISC_MAX_MD_SIZE if unsure). @digestlen
+ * is used to pass in the length of the digest buffer and returns the length
+ * of digest written to @digest.
+ */
+isc_result_t
+isc_hmac(const isc_md_type_t *type, const void *key, const size_t keylen,
+	 const unsigned char *buf, const size_t len, unsigned char *digest,
+	 unsigned int *digestlen);
+
+/**
+ * isc_hmac_new:
+ *
+ * This function allocates, initializes and returns HMAC context.
+ */
+isc_hmac_t *
+isc_hmac_new(void);
+
+/**
+ * isc_hmac_free:
+ * @md: HMAC context
+ *
+ * This function cleans up HMAC context and frees up the space allocated to it.
+ */
+void
+isc_hmac_free(isc_hmac_t *hmac);
+
+/**
+ * isc_hmac_init:
+ * @md: HMAC context
+ * @key: HMAC key
+ * @keylen: HMAC key length
+ * @type: digest type
+ *
+ * This function sets up HMAC context to use a hash function of @type and key
+ * @key which is @keylen bytes long.
+ */
+
+isc_result_t
+isc_hmac_init(isc_hmac_t *hmac, const void *key, const size_t keylen,
+	      const isc_md_type_t *type);
+
+/**
+ * isc_hmac_reset:
+ * @hmac: HMAC context
+ *
+ * This function resets the HMAC context.  This can be used to reuse an already
+ * existing context.
+ */
+isc_result_t
+isc_hmac_reset(isc_hmac_t *hmac);
+
+/**
+ * isc_hmac_update:
+ * @hmac: HMAC context
+ * @buf: data to hash
+ * @len: length of the data to hash
+ *
+ * This function can be called repeatedly with chunks of the message @buf to be
+ * authenticated which is @len bytes long.
+ */
+isc_result_t
+isc_hmac_update(isc_hmac_t *hmac, const unsigned char *buf, const size_t len);
+
+/**
+ * isc_hmac_final:
+ * @hmac: HMAC context
+ * @digest: the output buffer
+ * @digestlen: in: the length of @digest
+ *             out: the length of the data written to @digest
+ *
+ * This function retrieves the message authentication code from @hmac and places
+ * it in @digest, which must have space for the hash function output. @digestlen
+ * is used to pass in the length of the digest buffer and returns the length
+ * of digest written to @digest.  After calling this function no additional
+ * calls to isc_hmac_update() can be made.
+ */
+isc_result_t
+isc_hmac_final(isc_hmac_t *hmac, unsigned char *digest,
+	       unsigned int *digestlen);
+
+/**
+ * isc_hmac_md_type:
+ * @hmac: HMAC context
+ *
+ * This function return the isc_md_type_t previously set for the supplied
+ * HMAC context or NULL if no isc_md_type_t has been set.
+ */
+const isc_md_type_t *
+isc_hmac_get_md_type(isc_hmac_t *hmac);
+
+/**
+ * isc_hmac_get_size:
+ *
+ * This function return the size of the message digest when passed an isc_hmac_t
+ * structure, i.e. the size of the hash.
+ */
+size_t
+isc_hmac_get_size(isc_hmac_t *hmac);
+
+/**
+ * isc_hmac_get_block_size:
+ *
+ * This function return the block size of the message digest when passed an
+ * isc_hmac_t structure.
+ */
+int
+isc_hmac_get_block_size(isc_hmac_t *hmac);