/*
* Copyright (c) 2016 Thomas Pornin
*
* 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
#include
#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 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 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 accomodate 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^{30}
* (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