186 lines
6.5 KiB
C
186 lines
6.5 KiB
C
/*
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* Copyright (c) 2018 Thomas Pornin <pornin@bolet.org>
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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#ifndef BR_BEARSSL_KDF_H__
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#define BR_BEARSSL_KDF_H__
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#include <stddef.h>
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#include <stdint.h>
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#include "bearssl_hash.h"
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#include "bearssl_hmac.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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/** \file bearssl_kdf.h
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*
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* # Key Derivation Functions
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*
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* KDF are functions that takes a variable length input, and provide a
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* variable length output, meant to be used to derive subkeys from a
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* master key.
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*
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* ## HKDF
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*
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* HKDF is a KDF defined by [RFC 5869](https://tools.ietf.org/html/rfc5869).
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* It is based on HMAC, itself using an underlying hash function. Any
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* hash function can be used, as long as it is compatible with the rules
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* for the HMAC implementation (i.e. output size is 64 bytes or less, hash
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* internal state size is 64 bytes or less, and the internal block length is
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* a power of 2 between 16 and 256 bytes). HKDF has two phases:
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*
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* - HKDF-Extract: the input data in ingested, along with a "salt" value.
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*
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* - HKDF-Expand: the output is produced, from the result of processing
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* the input and salt, and using an extra non-secret parameter called
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* "info".
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*
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* The "salt" and "info" strings are non-secret and can be empty. Their role
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* is normally to bind the input and output, respectively, to conventional
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* identifiers that qualifu them within the used protocol or application.
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*
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* The implementation defined in this file uses the following functions:
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*
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* - `br_hkdf_init()`: initialize an HKDF context, with a hash function,
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* and the salt. This starts the HKDF-Extract process.
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*
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* - `br_hkdf_inject()`: inject more input bytes. This function may be
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* called repeatedly if the input data is provided by chunks.
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*
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* - `br_hkdf_flip()`: end the HKDF-Extract process, and start the
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* HKDF-Expand process.
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*
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* - `br_hkdf_produce()`: get the next bytes of output. This function
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* may be called several times to obtain the full output by chunks.
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* For correct HKDF processing, the same "info" string must be
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* provided for each call.
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*
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* Note that the HKDF total output size (the number of bytes that
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* HKDF-Expand is willing to produce) is limited: if the hash output size
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* is _n_ bytes, then the maximum output size is _255*n_.
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*/
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/**
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* \brief HKDF context.
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*
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* The HKDF context is initialized with a hash function implementation
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* and a salt value. Contents are opaque (callers should not access them
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* directly). The caller is responsible for allocating the context where
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* appropriate. Context initialisation and usage incurs no dynamic
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* allocation, so there is no release function.
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*/
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typedef struct {
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#ifndef BR_DOXYGEN_IGNORE
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union {
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br_hmac_context hmac_ctx;
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br_hmac_key_context prk_ctx;
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} u;
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unsigned char buf[64];
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size_t ptr;
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size_t dig_len;
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unsigned chunk_num;
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#endif
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} br_hkdf_context;
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/**
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* \brief HKDF context initialization.
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*
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* The underlying hash function and salt value are provided. Arbitrary
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* salt lengths can be used.
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*
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* HKDF makes a difference between a salt of length zero, and an
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* absent salt (the latter being equivalent to a salt consisting of
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* bytes of value zero, of the same length as the hash function output).
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* If `salt_len` is zero, then this function assumes that the salt is
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* present but of length zero. To specify an _absent_ salt, use
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* `BR_HKDF_NO_SALT` as `salt` parameter (`salt_len` is then ignored).
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*
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* \param hc HKDF context to initialise.
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* \param digest_vtable pointer to the hash function implementation vtable.
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* \param salt HKDF-Extract salt.
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* \param salt_len HKDF-Extract salt length (in bytes).
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*/
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void br_hkdf_init(br_hkdf_context *hc, const br_hash_class *digest_vtable,
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const void *salt, size_t salt_len);
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/**
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* \brief The special "absent salt" value for HKDF.
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*/
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#define BR_HKDF_NO_SALT (&br_hkdf_no_salt)
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#ifndef BR_DOXYGEN_IGNORE
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extern const unsigned char br_hkdf_no_salt;
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#endif
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/**
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* \brief HKDF input injection (HKDF-Extract).
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*
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* This function injects some more input bytes ("key material") into
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* HKDF. This function may be called several times, after `br_hkdf_init()`
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* but before `br_hkdf_flip()`.
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*
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* \param hc HKDF context.
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* \param ikm extra input bytes.
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* \param ikm_len number of extra input bytes.
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*/
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void br_hkdf_inject(br_hkdf_context *hc, const void *ikm, size_t ikm_len);
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/**
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* \brief HKDF switch to the HKDF-Expand phase.
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*
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* This call terminates the HKDF-Extract process (input injection), and
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* starts the HKDF-Expand process (output production).
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*
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* \param hc HKDF context.
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*/
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void br_hkdf_flip(br_hkdf_context *hc);
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/**
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* \brief HKDF output production (HKDF-Expand).
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*
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* Produce more output bytes from the current state. This function may be
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* called several times, but only after `br_hkdf_flip()`.
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*
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* Returned value is the number of actually produced bytes. The total
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* output length is limited to 255 times the output length of the
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* underlying hash function.
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*
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* \param hc HKDF context.
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* \param info application specific information string.
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* \param info_len application specific information string length (in bytes).
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* \param out destination buffer for the HKDF output.
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* \param out_len the length of the requested output (in bytes).
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* \return the produced output length (in bytes).
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*/
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size_t br_hkdf_produce(br_hkdf_context *hc,
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const void *info, size_t info_len, void *out, size_t out_len);
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#ifdef __cplusplus
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}
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#endif
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#endif
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