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+/*
+ * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef BR_BEARSSL_HMAC_H__
+#define BR_BEARSSL_HMAC_H__
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "bearssl_hash.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** \file bearssl_hmac.h
+ *
+ * # HMAC
+ *
+ * HMAC is initialized with a key and an underlying hash function; it
+ * then fills a "key context". That context contains the processed
+ * key.
+ *
+ * With the key context, a HMAC context can be initialized to process
+ * the input bytes and obtain the MAC output. The key context is not
+ * modified during that process, and can be reused.
+ *
+ * IMPORTANT: HMAC shall be used only with functions that have the
+ * following properties:
+ *
+ * - hash output size does not exceed 64 bytes;
+ * - hash internal state size does not exceed 64 bytes;
+ * - internal block length is a power of 2 between 16 and 256 bytes.
+ */
+
+/**
+ * \brief HMAC key context.
+ *
+ * The HMAC key context is initialised with a hash function implementation
+ * and a secret key. Contents are opaque (callers should not access them
+ * directly). The caller is responsible for allocating the context where
+ * appropriate. Context initialisation and usage incurs no dynamic
+ * allocation, so there is no release function.
+ */
+typedef struct {
+#ifndef BR_DOXYGEN_IGNORE
+ const br_hash_class *dig_vtable;
+ unsigned char ksi[64], kso[64];
+#endif
+} br_hmac_key_context;
+
+/**
+ * \brief HMAC key context initialisation.
+ *
+ * Initialise the key context with the provided key, using the hash function
+ * identified by `digest_vtable`. This supports arbitrary key lengths.
+ *
+ * \param kc HMAC key context to initialise.
+ * \param digest_vtable pointer to the hash function implementation vtable.
+ * \param key pointer to the HMAC secret key.
+ * \param key_len HMAC secret key length (in bytes).
+ */
+void br_hmac_key_init(br_hmac_key_context *kc,
+ const br_hash_class *digest_vtable, const void *key, size_t key_len);
+
+/*
+ * \brief Get the underlying hash function.
+ *
+ * This function returns a pointer to the implementation vtable of the
+ * hash function used for this HMAC key context.
+ *
+ * \param kc HMAC key context.
+ * \return the hash function implementation.
+ */
+static inline const br_hash_class *br_hmac_key_get_digest(
+ const br_hmac_key_context *kc)
+{
+ return kc->dig_vtable;
+}
+
+/**
+ * \brief HMAC computation context.
+ *
+ * The HMAC computation context maintains the state for a single HMAC
+ * computation. It is modified as input bytes are injected. The context
+ * is caller-allocated and has no release function since it does not
+ * dynamically allocate external resources. Its contents are opaque.
+ */
+typedef struct {
+#ifndef BR_DOXYGEN_IGNORE
+ br_hash_compat_context dig;
+ unsigned char kso[64];
+ size_t out_len;
+#endif
+} br_hmac_context;
+
+/**
+ * \brief HMAC computation initialisation.
+ *
+ * Initialise a HMAC context with a key context. The key context is
+ * unmodified. Relevant data from the key context is immediately copied;
+ * the key context can thus be independently reused, modified or released
+ * without impacting this HMAC computation.
+ *
+ * An explicit output length can be specified; the actual output length
+ * will be the minimum of that value and the natural HMAC output length.
+ * If `out_len` is 0, then the natural HMAC output length is selected. The
+ * "natural output length" is the output length of the underlying hash
+ * function.
+ *
+ * \param ctx HMAC context to initialise.
+ * \param kc HMAC key context (already initialised with the key).
+ * \param out_len HMAC output length (0 to select "natural length").
+ */
+void br_hmac_init(br_hmac_context *ctx,
+ const br_hmac_key_context *kc, size_t out_len);
+
+/**
+ * \brief Get the HMAC output size.
+ *
+ * The HMAC output size is the number of bytes that will actually be
+ * produced with `br_hmac_out()` with the provided context. This function
+ * MUST NOT be called on a non-initialised HMAC computation context.
+ * The returned value is the minimum of the HMAC natural length (output
+ * size of the underlying hash function) and the `out_len` parameter which
+ * was used with the last `br_hmac_init()` call on that context (if the
+ * initialisation `out_len` parameter was 0, then this function will
+ * return the HMAC natural length).
+ *
+ * \param ctx the (already initialised) HMAC computation context.
+ * \return the HMAC actual output size.
+ */
+static inline size_t
+br_hmac_size(br_hmac_context *ctx)
+{
+ return ctx->out_len;
+}
+
+/*
+ * \brief Get the underlying hash function.
+ *
+ * This function returns a pointer to the implementation vtable of the
+ * hash function used for this HMAC context.
+ *
+ * \param hc HMAC context.
+ * \return the hash function implementation.
+ */
+static inline const br_hash_class *br_hmac_get_digest(
+ const br_hmac_context *hc)
+{
+ return hc->dig.vtable;
+}
+
+/**
+ * \brief Inject some bytes in HMAC.
+ *
+ * The provided `len` bytes are injected as extra input in the HMAC
+ * computation incarnated by the `ctx` HMAC context. It is acceptable
+ * that `len` is zero, in which case `data` is ignored (and may be
+ * `NULL`) and this function does nothing.
+ */
+void br_hmac_update(br_hmac_context *ctx, const void *data, size_t len);
+
+/**
+ * \brief Compute the HMAC output.
+ *
+ * The destination buffer MUST be large enough to accommodate the result;
+ * its length is at most the "natural length" of HMAC (i.e. the output
+ * length of the underlying hash function). The context is NOT modified;
+ * further bytes may be processed. Thus, "partial HMAC" values can be
+ * efficiently obtained.
+ *
+ * Returned value is the output length (in bytes).
+ *
+ * \param ctx HMAC computation context.
+ * \param out destination buffer for the HMAC output.
+ * \return the produced value length (in bytes).
+ */
+size_t br_hmac_out(const br_hmac_context *ctx, void *out);
+
+/**
+ * \brief Constant-time HMAC computation.
+ *
+ * This function compute the HMAC output in constant time. Some extra
+ * input bytes are processed, then the output is computed. The extra
+ * input consists in the `len` bytes pointed to by `data`. The `len`
+ * parameter must lie between `min_len` and `max_len` (inclusive);
+ * `max_len` bytes are actually read from `data`. Computing time (and
+ * memory access pattern) will not depend upon the data byte contents or
+ * the value of `len`.
+ *
+ * The output is written in the `out` buffer, that MUST be large enough
+ * to receive it.
+ *
+ * The difference `max_len - min_len` MUST be less than 2<sup>30</sup>
+ * (i.e. about one gigabyte).
+ *
+ * This function computes the output properly only if the underlying
+ * hash function uses MD padding (i.e. MD5, SHA-1, SHA-224, SHA-256,
+ * SHA-384 or SHA-512).
+ *
+ * The provided context is NOT modified.
+ *
+ * \param ctx the (already initialised) HMAC computation context.
+ * \param data the extra input bytes.
+ * \param len the extra input length (in bytes).
+ * \param min_len minimum extra input length (in bytes).
+ * \param max_len maximum extra input length (in bytes).
+ * \param out destination buffer for the HMAC output.
+ * \return the produced value length (in bytes).
+ */
+size_t br_hmac_outCT(const br_hmac_context *ctx,
+ const void *data, size_t len, size_t min_len, size_t max_len,
+ void *out);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif