#include "bearssl_hash.h"
-/*
- * HMAC
- * ----
+#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
*
* 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
+ *
+ * - 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.
*/
-/*
- * Key context.
+/**
+ * \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;
-/*
- * Initialize the key context with the provided key, using the hash function
- * identified by digest_class.
+/**
+ * \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_class, const void *key, size_t key_len);
+ const br_hash_class *digest_vtable, const void *key, size_t key_len);
/*
- * A helper structure that is big enough to accommodate all context
- * structures for all hash functions for which HMAC is supported.
+ * \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.
*/
-typedef union {
- const br_hash_class *vtable;
- br_md5_context md5;
- br_sha1_context sha1;
- br_sha224_context sha224;
- br_sha256_context sha256;
- br_sha384_context sha384;
- br_sha512_context sha512;
-} br_hmac_allhash_context;
+static inline const br_hash_class *br_hmac_key_get_digest(
+ const br_hmac_key_context *kc)
+{
+ return kc->dig_vtable;
+}
-/*
- * Context for an HMAC computation.
+/**
+ * \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 {
- br_hmac_allhash_context dig;
+#ifndef BR_DOXYGEN_IGNORE
+ br_hash_compat_context dig;
unsigned char kso[64];
size_t out_len;
+#endif
} br_hmac_context;
-/*
- * Initialize a HMAC context with a key context. The key context is
+/**
+ * \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.
+ * 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);
-/*
- * Get the MAC output size. The context must have been initialized.
+/**
+ * \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.
*/
-#define br_hmac_size(ctx) ((ctx)->out_len)
+static inline size_t
+br_hmac_size(br_hmac_context *ctx)
+{
+ return ctx->out_len;
+}
/*
- * Process some more bytes.
+ * \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);
-/*
- * Compute the HMAC output. The destination buffer MUST be large enough
- * to accomodate the result. The context is NOT modified; further bytes
- * may be processed. Thus, "partial HMAC" values can be efficiently
- * obtained.
+/**
+ * \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);
-/*
- * 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 bytes or the value of 'len'.
- *
- * The output is written in the 'out' buffer, that MUST be large enough
+/**
+ * \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 2^30.
+ * 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,
*
* The provided context is NOT modified.
*
- * Returned value is the MAC length (in bytes).
+ * \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
projects / BearSSL / blobdiff