/*
* 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_RAND_H__
#define BR_BEARSSL_RAND_H__
#include <stddef.h>
#include <stdint.h>
#include "bearssl_block.h"
#include "bearssl_hash.h"
#ifdef __cplusplus
extern "C" {
#endif
/** \file bearssl_rand.h
*
* # Pseudo-Random Generators
*
* A PRNG is a state-based engine that outputs pseudo-random bytes on
* demand. It is initialized with an initial seed, and additional seed
* bytes can be added afterwards. Bytes produced depend on the seeds and
* also on the exact sequence of calls (including sizes requested for
* each call).
*
*
* ## Procedural and OOP API
*
* For the PRNG of name "`xxx`", two API are provided. The _procedural_
* API defined a context structure `br_xxx_context` and three functions:
*
* - `br_xxx_init()`
*
* Initialise the context with an initial seed.
*
* - `br_xxx_generate()`
*
* Produce some pseudo-random bytes.
*
* - `br_xxx_update()`
*
* Inject some additional seed.
*
* The initialisation function sets the first context field (`vtable`)
* to a pointer to the vtable that supports the OOP API. The OOP API
* provides access to the same functions through function pointers,
* named `init()`, `generate()` and `update()`.
*
* Note that the context initialisation method may accept additional
* parameters, provided as a 'const void *' pointer at API level. These
* additional parameters depend on the implemented PRNG.
*
*
* ## HMAC_DRBG
*
* HMAC_DRBG is defined in [NIST SP 800-90A Revision
* 1](http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-90Ar1.pdf).
* It uses HMAC repeatedly, over some configurable underlying hash
* function. In BearSSL, it is implemented under the "`hmac_drbg`" name.
* The "extra parameters" pointer for context initialisation should be
* set to a pointer to the vtable for the underlying hash function (e.g.
* pointer to `br_sha256_vtable` to use HMAC_DRBG with SHA-256).
*
* According to the NIST standard, each request shall produce up to
* 2<sup>19</sup> bits (i.e. 64 kB of data); moreover, the context shall
* be reseeded at least once every 2<sup>48</sup> requests. This
* implementation does not maintain the reseed counter (the threshold is
* too high to be reached in practice) and does not object to producing
* more than 64 kB in a single request; thus, the code cannot fail,
* which corresponds to the fact that the API has no room for error
* codes. However, this implies that requesting more than 64 kB in one
* `generate()` request, or making more than 2<sup>48</sup> requests
* without reseeding, is formally out of NIST specification. There is
* no currently known security penalty for exceeding the NIST limits,
* and, in any case, HMAC_DRBG usage in implementing SSL/TLS always
* stays much below these thresholds.
*
*
* ## AESCTR_DRBG
*
* AESCTR_DRBG is a custom PRNG based on AES-128 in CTR mode. This is
* meant to be used only in situations where you are desperate for
* speed, and have an hardware-optimized AES/CTR implementation. Whether
* this will yield perceptible improvements depends on what you use the
* pseudorandom bytes for, and how many you want; for instance, RSA key
* pair generation uses a substantial amount of randomness, and using
* AESCTR_DRBG instead of HMAC_DRBG yields a 15 to 20% increase in key
* generation speed on a recent x86 CPU (Intel Core i7-6567U at 3.30 GHz).
*
* Internally, it uses CTR mode with successive counter values, starting
* at zero (counter value expressed over 128 bits, big-endian convention).
* The counter is not allowed to reach 32768; thus, every 32768*16 bytes
* at most, the `update()` function is run (on an empty seed, if none is
* provided). The `update()` function computes the new AES-128 key by
* applying a custom hash function to the concatenation of a state-dependent
* word (encryption of an all-one block with the current key) and the new
* seed. The custom hash function uses Hirose's construction over AES-256;
* see the comments in `aesctr_drbg.c` for details.
*
* This DRBG does not follow an existing standard, and thus should be
* considered as inadequate for production use until it has been properly
* analysed.
*/
/**
* \brief Class type for PRNG implementations.
*
* A `br_prng_class` instance references the methods implementing a PRNG.
* Constant instances of this structure are defined for each implemented
* PRNG. Such instances are also called "vtables".
*/
typedef struct br_prng_class_ br_prng_class;
struct br_prng_class_ {
/**
* \brief Size (in bytes) of the context structure appropriate for
* running this PRNG.
*/
size_t context_size;
/**
* \brief Initialisation method.
*
* The context to initialise is provided as a pointer to its
* first field (the vtable pointer); this function sets that
* first field to a pointer to the vtable.
*
* The extra parameters depend on the implementation; each
* implementation defines what kind of extra parameters it
* expects (if any).
*
* Requirements on the initial seed depend on the implemented
* PRNG.
*
* \param ctx PRNG context to initialise.
* \param params extra parameters for the PRNG.
* \param seed initial seed.
* \param seed_len initial seed length (in bytes).
*/
void (*init)(const br_prng_class **ctx, const void *params,
const void *seed, size_t seed_len);
/**
* \brief Random bytes generation.
*
* This method produces `len` pseudorandom bytes, in the `out`
* buffer. The context is updated accordingly.
*
* \param ctx PRNG context.
* \param out output buffer.
* \param len number of pseudorandom bytes to produce.
*/
void (*generate)(const br_prng_class **ctx, void *out, size_t len);
/**
* \brief Inject additional seed bytes.
*
* The provided seed bytes are added into the PRNG internal
* entropy pool.
*
* \param ctx PRNG context.
* \param seed additional seed.
* \param seed_len additional seed length (in bytes).
*/
void (*update)(const br_prng_class **ctx,
const void *seed, size_t seed_len);
};
/**
* \brief Context for HMAC_DRBG.
*
* The context contents are opaque, except the first field, which
* supports OOP.
*/
typedef struct {
/**
* \brief Pointer to the vtable.
*
* This field is set with the initialisation method/function.
*/
const br_prng_class *vtable;
#ifndef BR_DOXYGEN_IGNORE
unsigned char K[64];
unsigned char V[64];
const br_hash_class *digest_class;
#endif
} br_hmac_drbg_context;
/**
* \brief Statically allocated, constant vtable for HMAC_DRBG.
*/
extern const br_prng_class br_hmac_drbg_vtable;
/**
* \brief HMAC_DRBG initialisation.
*
* The context to initialise is provided as a pointer to its first field
* (the vtable pointer); this function sets that first field to a
* pointer to the vtable.
*
* The `seed` value is what is called, in NIST terminology, the
* concatenation of the "seed", "nonce" and "personalization string", in
* that order.
*
* The `digest_class` parameter defines the underlying hash function.
* Formally, the NIST standard specifies that the hash function shall
* be only SHA-1 or one of the SHA-2 functions. This implementation also
* works with any other implemented hash function (such as MD5), but
* this is non-standard and therefore not recommended.
*
* \param ctx HMAC_DRBG context to initialise.
* \param digest_class vtable for the underlying hash function.
* \param seed initial seed.
* \param seed_len initial seed length (in bytes).
*/
void br_hmac_drbg_init(br_hmac_drbg_context *ctx,
const br_hash_class *digest_class, const void *seed, size_t seed_len);
/**
* \brief Random bytes generation with HMAC_DRBG.
*
* This method produces `len` pseudorandom bytes, in the `out`
* buffer. The context is updated accordingly. Formally, requesting
* more than 65536 bytes in one request falls out of specification
* limits (but it won't fail).
*
* \param ctx HMAC_DRBG context.
* \param out output buffer.
* \param len number of pseudorandom bytes to produce.
*/
void br_hmac_drbg_generate(br_hmac_drbg_context *ctx, void *out, size_t len);
/**
* \brief Inject additional seed bytes in HMAC_DRBG.
*
* The provided seed bytes are added into the HMAC_DRBG internal
* entropy pool. The process does not _replace_ existing entropy,
* thus pushing non-random bytes (i.e. bytes which are known to the
* attackers) does not degrade the overall quality of generated bytes.
*
* \param ctx HMAC_DRBG context.
* \param seed additional seed.
* \param seed_len additional seed length (in bytes).
*/
void br_hmac_drbg_update(br_hmac_drbg_context *ctx,
const void *seed, size_t seed_len);
/**
* \brief Get the hash function implementation used by a given instance of
* HMAC_DRBG.
*
* This calls MUST NOT be performed on a context which was not
* previously initialised.
*
* \param ctx HMAC_DRBG context.
* \return the hash function vtable.
*/
static inline const br_hash_class *
br_hmac_drbg_get_hash(const br_hmac_drbg_context *ctx)
{
return ctx->digest_class;
}
/**
* \brief Type for a provider of entropy seeds.
*
* A "seeder" is a function that is able to obtain random values from
* some source and inject them as entropy seed in a PRNG. A seeder
* shall guarantee that the total entropy of the injected seed is large
* enough to seed a PRNG for purposes of cryptographic key generation
* (i.e. at least 128 bits).
*
* A seeder may report a failure to obtain adequate entropy. Seeders
* shall endeavour to fix themselves transient errors by trying again;
* thus, callers may consider reported errors as permanent.
*
* \param ctx PRNG context to seed.
* \return 1 on success, 0 on error.
*/
typedef int (*br_prng_seeder)(const br_prng_class **ctx);
/**
* \brief Get a seeder backed by the operating system or hardware.
*
* Get a seeder that feeds on RNG facilities provided by the current
* operating system or hardware. If no such facility is known, then 0
* is returned.
*
* If `name` is not `NULL`, then `*name` is set to a symbolic string
* that identifies the seeder implementation. If no seeder is returned
* and `name` is not `NULL`, then `*name` is set to a pointer to the
* constant string `"none"`.
*
* \param name receiver for seeder name, or `NULL`.
* \return the system seeder, if available, or 0.
*/
br_prng_seeder br_prng_seeder_system(const char **name);
/**
* \brief Context for AESCTR_DRBG.
*
* The context contents are opaque, except the first field, which
* supports OOP.
*/
typedef struct {
/**
* \brief Pointer to the vtable.
*
* This field is set with the initialisation method/function.
*/
const br_prng_class *vtable;
#ifndef BR_DOXYGEN_IGNORE
br_aes_gen_ctr_keys sk;
uint32_t cc;
#endif
} br_aesctr_drbg_context;
/**
* \brief Statically allocated, constant vtable for AESCTR_DRBG.
*/
extern const br_prng_class br_aesctr_drbg_vtable;
/**
* \brief AESCTR_DRBG initialisation.
*
* The context to initialise is provided as a pointer to its first field
* (the vtable pointer); this function sets that first field to a
* pointer to the vtable.
*
* The internal AES key is first set to the all-zero key; then, the
* `br_aesctr_drbg_update()` function is called with the provided `seed`.
* The call is performed even if the seed length (`seed_len`) is zero.
*
* The `aesctr` parameter defines the underlying AES/CTR implementation.
*
* \param ctx AESCTR_DRBG context to initialise.
* \param aesctr vtable for the AES/CTR implementation.
* \param seed initial seed (can be `NULL` if `seed_len` is zero).
* \param seed_len initial seed length (in bytes).
*/
void br_aesctr_drbg_init(br_aesctr_drbg_context *ctx,
const br_block_ctr_class *aesctr, const void *seed, size_t seed_len);
/**
* \brief Random bytes generation with AESCTR_DRBG.
*
* This method produces `len` pseudorandom bytes, in the `out`
* buffer. The context is updated accordingly.
*
* \param ctx AESCTR_DRBG context.
* \param out output buffer.
* \param len number of pseudorandom bytes to produce.
*/
void br_aesctr_drbg_generate(br_aesctr_drbg_context *ctx,
void *out, size_t len);
/**
* \brief Inject additional seed bytes in AESCTR_DRBG.
*
* The provided seed bytes are added into the AESCTR_DRBG internal
* entropy pool. The process does not _replace_ existing entropy,
* thus pushing non-random bytes (i.e. bytes which are known to the
* attackers) does not degrade the overall quality of generated bytes.
*
* \param ctx AESCTR_DRBG context.
* \param seed additional seed.
* \param seed_len additional seed length (in bytes).
*/
void br_aesctr_drbg_update(br_aesctr_drbg_context *ctx,
const void *seed, size_t seed_len);
#ifdef __cplusplus
}
#endif
#endif