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/**
* \file ctr_drbg.h
*
* \brief This file contains definitions and functions for the
* CTR_DRBG pseudorandom generator.
*
* CTR_DRBG is a standardized way of building a PRNG from a block-cipher
* in counter mode operation, as defined in <em>NIST SP 800-90A:
* Recommendation for Random Number Generation Using Deterministic Random
* Bit Generators</em>.
*
* The Mbed TLS implementation of CTR_DRBG uses AES-256 (default) or AES-128
* (if \c MBEDTLS_CTR_DRBG_USE_128_BIT_KEY is enabled at compile time)
* as the underlying block cipher, with a derivation function.
*
* The security strength as defined in NIST SP 800-90A is
* 128 bits when AES-128 is used (\c MBEDTLS_CTR_DRBG_USE_128_BIT_KEY enabled)
* and 256 bits otherwise, provided that #MBEDTLS_CTR_DRBG_ENTROPY_LEN is
* kept at its default value (and not overridden in mbedtls_config.h) and that the
* DRBG instance is set up with default parameters.
* See the documentation of mbedtls_ctr_drbg_seed() for more
* information.
*/
/*
* Copyright The Mbed TLS Contributors
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef MBEDTLS_CTR_DRBG_H
#define MBEDTLS_CTR_DRBG_H
#include "mbedtls/private_access.h"
#include "mbedtls/build_info.h"
#include "mbedtls/aes.h"
#if defined(MBEDTLS_THREADING_C)
#include "mbedtls/threading.h"
#endif
/** The entropy source failed. */
#define MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED -0x0034
/** The requested random buffer length is too big. */
#define MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG -0x0036
/** The input (entropy + additional data) is too large. */
#define MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG -0x0038
/** Read or write error in file. */
#define MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR -0x003A
#define MBEDTLS_CTR_DRBG_BLOCKSIZE 16 /**< The block size used by the cipher. */
#if defined(MBEDTLS_CTR_DRBG_USE_128_BIT_KEY)
#define MBEDTLS_CTR_DRBG_KEYSIZE 16
/**< The key size in bytes used by the cipher.
*
* Compile-time choice: 16 bytes (128 bits)
* because #MBEDTLS_CTR_DRBG_USE_128_BIT_KEY is enabled.
*/
#else
#define MBEDTLS_CTR_DRBG_KEYSIZE 32
/**< The key size in bytes used by the cipher.
*
* Compile-time choice: 32 bytes (256 bits)
* because \c MBEDTLS_CTR_DRBG_USE_128_BIT_KEY is disabled.
*/
#endif
#define MBEDTLS_CTR_DRBG_KEYBITS ( MBEDTLS_CTR_DRBG_KEYSIZE * 8 ) /**< The key size for the DRBG operation, in bits. */
#define MBEDTLS_CTR_DRBG_SEEDLEN ( MBEDTLS_CTR_DRBG_KEYSIZE + MBEDTLS_CTR_DRBG_BLOCKSIZE ) /**< The seed length, calculated as (counter + AES key). */
/**
* \name SECTION: Module settings
*
* The configuration options you can set for this module are in this section.
* Either change them in mbedtls_config.h or define them using the compiler command
* line.
* \{
*/
/** \def MBEDTLS_CTR_DRBG_ENTROPY_LEN
*
* \brief The amount of entropy used per seed by default, in bytes.
*/
#if !defined(MBEDTLS_CTR_DRBG_ENTROPY_LEN)
#if defined(MBEDTLS_SHA512_C) && !defined(MBEDTLS_ENTROPY_FORCE_SHA256)
/** This is 48 bytes because the entropy module uses SHA-512
* (\c MBEDTLS_ENTROPY_FORCE_SHA256 is disabled).
*/
#define MBEDTLS_CTR_DRBG_ENTROPY_LEN 48
#else /* defined(MBEDTLS_SHA512_C) && !defined(MBEDTLS_ENTROPY_FORCE_SHA256) */
/** This is 32 bytes because the entropy module uses SHA-256
* (the SHA512 module is disabled or
* \c MBEDTLS_ENTROPY_FORCE_SHA256 is enabled).
*/
#if !defined(MBEDTLS_CTR_DRBG_USE_128_BIT_KEY)
/** \warning To achieve a 256-bit security strength, you must pass a nonce
* to mbedtls_ctr_drbg_seed().
*/
#endif /* !defined(MBEDTLS_CTR_DRBG_USE_128_BIT_KEY) */
#define MBEDTLS_CTR_DRBG_ENTROPY_LEN 32
#endif /* defined(MBEDTLS_SHA512_C) && !defined(MBEDTLS_ENTROPY_FORCE_SHA256) */
#endif /* !defined(MBEDTLS_CTR_DRBG_ENTROPY_LEN) */
#if !defined(MBEDTLS_CTR_DRBG_RESEED_INTERVAL)
#define MBEDTLS_CTR_DRBG_RESEED_INTERVAL 10000
/**< The interval before reseed is performed by default. */
#endif
#if !defined(MBEDTLS_CTR_DRBG_MAX_INPUT)
#define MBEDTLS_CTR_DRBG_MAX_INPUT 256
/**< The maximum number of additional input Bytes. */
#endif
#if !defined(MBEDTLS_CTR_DRBG_MAX_REQUEST)
#define MBEDTLS_CTR_DRBG_MAX_REQUEST 1024
/**< The maximum number of requested Bytes per call. */
#endif
#if !defined(MBEDTLS_CTR_DRBG_MAX_SEED_INPUT)
#define MBEDTLS_CTR_DRBG_MAX_SEED_INPUT 384
/**< The maximum size of seed or reseed buffer in bytes. */
#endif
/** \} name SECTION: Module settings */
#define MBEDTLS_CTR_DRBG_PR_OFF 0
/**< Prediction resistance is disabled. */
#define MBEDTLS_CTR_DRBG_PR_ON 1
/**< Prediction resistance is enabled. */
#ifdef __cplusplus
extern "C" {
#endif
#if MBEDTLS_CTR_DRBG_ENTROPY_LEN >= MBEDTLS_CTR_DRBG_KEYSIZE * 3 / 2
/** The default length of the nonce read from the entropy source.
*
* This is \c 0 because a single read from the entropy source is sufficient
* to include a nonce.
* See the documentation of mbedtls_ctr_drbg_seed() for more information.
*/
#define MBEDTLS_CTR_DRBG_ENTROPY_NONCE_LEN 0
#else
/** The default length of the nonce read from the entropy source.
*
* This is half of the default entropy length because a single read from
* the entropy source does not provide enough material to form a nonce.
* See the documentation of mbedtls_ctr_drbg_seed() for more information.
*/
#define MBEDTLS_CTR_DRBG_ENTROPY_NONCE_LEN ( MBEDTLS_CTR_DRBG_ENTROPY_LEN + 1 ) / 2
#endif
/**
* \brief The CTR_DRBG context structure.
*/
typedef struct mbedtls_ctr_drbg_context
{
unsigned char MBEDTLS_PRIVATE(counter)[16]; /*!< The counter (V). */
int MBEDTLS_PRIVATE(reseed_counter); /*!< The reseed counter.
* This is the number of requests that have
* been made since the last (re)seeding,
* minus one.
* Before the initial seeding, this field
* contains the amount of entropy in bytes
* to use as a nonce for the initial seeding,
* or -1 if no nonce length has been explicitly
* set (see mbedtls_ctr_drbg_set_nonce_len()).
*/
int MBEDTLS_PRIVATE(prediction_resistance); /*!< This determines whether prediction
resistance is enabled, that is
whether to systematically reseed before
each random generation. */
size_t MBEDTLS_PRIVATE(entropy_len); /*!< The amount of entropy grabbed on each
seed or reseed operation, in bytes. */
int MBEDTLS_PRIVATE(reseed_interval); /*!< The reseed interval.
* This is the maximum number of requests
* that can be made between reseedings. */
mbedtls_aes_context MBEDTLS_PRIVATE(aes_ctx); /*!< The AES context. */
/*
* Callbacks (Entropy)
*/
int (*MBEDTLS_PRIVATE(f_entropy))(void *, unsigned char *, size_t);
/*!< The entropy callback function. */
void *MBEDTLS_PRIVATE(p_entropy); /*!< The context for the entropy function. */
#if defined(MBEDTLS_THREADING_C)
/* Invariant: the mutex is initialized if and only if f_entropy != NULL.
* This means that the mutex is initialized during the initial seeding
* in mbedtls_ctr_drbg_seed() and freed in mbedtls_ctr_drbg_free().
*
* Note that this invariant may change without notice. Do not rely on it
* and do not access the mutex directly in application code.
*/
mbedtls_threading_mutex_t MBEDTLS_PRIVATE(mutex);
#endif
}
mbedtls_ctr_drbg_context;
/**
* \brief This function initializes the CTR_DRBG context,
* and prepares it for mbedtls_ctr_drbg_seed()
* or mbedtls_ctr_drbg_free().
*
* \note The reseed interval is
* #MBEDTLS_CTR_DRBG_RESEED_INTERVAL by default.
* You can override it by calling
* mbedtls_ctr_drbg_set_reseed_interval().
*
* \param ctx The CTR_DRBG context to initialize.
*/
void mbedtls_ctr_drbg_init( mbedtls_ctr_drbg_context *ctx );
/**
* \brief This function seeds and sets up the CTR_DRBG
* entropy source for future reseeds.
*
* A typical choice for the \p f_entropy and \p p_entropy parameters is
* to use the entropy module:
* - \p f_entropy is mbedtls_entropy_func();
* - \p p_entropy is an instance of ::mbedtls_entropy_context initialized
* with mbedtls_entropy_init() (which registers the platform's default
* entropy sources).
*
* The entropy length is #MBEDTLS_CTR_DRBG_ENTROPY_LEN by default.
* You can override it by calling mbedtls_ctr_drbg_set_entropy_len().
*
* The entropy nonce length is:
* - \c 0 if the entropy length is at least 3/2 times the entropy length,
* which guarantees that the security strength is the maximum permitted
* by the key size and entropy length according to NIST SP 800-90A §10.2.1;
* - Half the entropy length otherwise.
* You can override it by calling mbedtls_ctr_drbg_set_nonce_len().
* With the default entropy length, the entropy nonce length is
* #MBEDTLS_CTR_DRBG_ENTROPY_NONCE_LEN.
*
* You can provide a nonce and personalization string in addition to the
* entropy source, to make this instantiation as unique as possible.
* See SP 800-90A §8.6.7 for more details about nonces.
*
* The _seed_material_ value passed to the derivation function in
* the CTR_DRBG Instantiate Process described in NIST SP 800-90A §10.2.1.3.2
* is the concatenation of the following strings:
* - A string obtained by calling \p f_entropy function for the entropy
* length.
*/
#if MBEDTLS_CTR_DRBG_ENTROPY_NONCE_LEN == 0
/**
* - If mbedtls_ctr_drbg_set_nonce_len() has been called, a string
* obtained by calling \p f_entropy function for the specified length.
*/
#else
/**
* - A string obtained by calling \p f_entropy function for the entropy nonce
* length. If the entropy nonce length is \c 0, this function does not
* make a second call to \p f_entropy.
*/
#endif
#if defined(MBEDTLS_THREADING_C)
/**
* \note When Mbed TLS is built with threading support,
* after this function returns successfully,
* it is safe to call mbedtls_ctr_drbg_random()
* from multiple threads. Other operations, including
* reseeding, are not thread-safe.
*/
#endif /* MBEDTLS_THREADING_C */
/**
* - The \p custom string.
*
* \note To achieve the nominal security strength permitted
* by CTR_DRBG, the entropy length must be:
* - at least 16 bytes for a 128-bit strength
* (maximum achievable strength when using AES-128);
* - at least 32 bytes for a 256-bit strength
* (maximum achievable strength when using AES-256).
*
* In addition, if you do not pass a nonce in \p custom,
* the sum of the entropy length
* and the entropy nonce length must be:
* - at least 24 bytes for a 128-bit strength
* (maximum achievable strength when using AES-128);
* - at least 48 bytes for a 256-bit strength
* (maximum achievable strength when using AES-256).
*
* \param ctx The CTR_DRBG context to seed.
* It must have been initialized with
* mbedtls_ctr_drbg_init().
* After a successful call to mbedtls_ctr_drbg_seed(),
* you may not call mbedtls_ctr_drbg_seed() again on
* the same context unless you call
* mbedtls_ctr_drbg_free() and mbedtls_ctr_drbg_init()
* again first.
* After a failed call to mbedtls_ctr_drbg_seed(),
* you must call mbedtls_ctr_drbg_free().
* \param f_entropy The entropy callback, taking as arguments the
* \p p_entropy context, the buffer to fill, and the
* length of the buffer.
* \p f_entropy is always called with a buffer size
* less than or equal to the entropy length.
* \param p_entropy The entropy context to pass to \p f_entropy.
* \param custom The personalization string.
* This can be \c NULL, in which case the personalization
* string is empty regardless of the value of \p len.
* \param len The length of the personalization string.
* This must be at most
* #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT
* - #MBEDTLS_CTR_DRBG_ENTROPY_LEN.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure.
*/
int mbedtls_ctr_drbg_seed( mbedtls_ctr_drbg_context *ctx,
int (*f_entropy)(void *, unsigned char *, size_t),
void *p_entropy,
const unsigned char *custom,
size_t len );
/**
* \brief This function resets CTR_DRBG context to the state immediately
* after initial call of mbedtls_ctr_drbg_init().
*
* \param ctx The CTR_DRBG context to clear.
*/
void mbedtls_ctr_drbg_free( mbedtls_ctr_drbg_context *ctx );
/**
* \brief This function turns prediction resistance on or off.
* The default value is off.
*
* \note If enabled, entropy is gathered at the beginning of
* every call to mbedtls_ctr_drbg_random_with_add()
* or mbedtls_ctr_drbg_random().
* Only use this if your entropy source has sufficient
* throughput.
*
* \param ctx The CTR_DRBG context.
* \param resistance #MBEDTLS_CTR_DRBG_PR_ON or #MBEDTLS_CTR_DRBG_PR_OFF.
*/
void mbedtls_ctr_drbg_set_prediction_resistance( mbedtls_ctr_drbg_context *ctx,
int resistance );
/**
* \brief This function sets the amount of entropy grabbed on each
* seed or reseed.
*
* The default value is #MBEDTLS_CTR_DRBG_ENTROPY_LEN.
*
* \note The security strength of CTR_DRBG is bounded by the
* entropy length. Thus:
* - When using AES-256
* (\c MBEDTLS_CTR_DRBG_USE_128_BIT_KEY is disabled,
* which is the default),
* \p len must be at least 32 (in bytes)
* to achieve a 256-bit strength.
* - When using AES-128
* (\c MBEDTLS_CTR_DRBG_USE_128_BIT_KEY is enabled)
* \p len must be at least 16 (in bytes)
* to achieve a 128-bit strength.
*
* \param ctx The CTR_DRBG context.
* \param len The amount of entropy to grab, in bytes.
* This must be at most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT
* and at most the maximum length accepted by the
* entropy function that is set in the context.
*/
void mbedtls_ctr_drbg_set_entropy_len( mbedtls_ctr_drbg_context *ctx,
size_t len );
/**
* \brief This function sets the amount of entropy grabbed
* as a nonce for the initial seeding.
*
* Call this function before calling mbedtls_ctr_drbg_seed() to read
* a nonce from the entropy source during the initial seeding.
*
* \param ctx The CTR_DRBG context.
* \param len The amount of entropy to grab for the nonce, in bytes.
* This must be at most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT
* and at most the maximum length accepted by the
* entropy function that is set in the context.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG if \p len is
* more than #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT.
* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED
* if the initial seeding has already taken place.
*/
int mbedtls_ctr_drbg_set_nonce_len( mbedtls_ctr_drbg_context *ctx,
size_t len );
/**
* \brief This function sets the reseed interval.
*
* The reseed interval is the number of calls to mbedtls_ctr_drbg_random()
* or mbedtls_ctr_drbg_random_with_add() after which the entropy function
* is called again.
*
* The default value is #MBEDTLS_CTR_DRBG_RESEED_INTERVAL.
*
* \param ctx The CTR_DRBG context.
* \param interval The reseed interval.
*/
void mbedtls_ctr_drbg_set_reseed_interval( mbedtls_ctr_drbg_context *ctx,
int interval );
/**
* \brief This function reseeds the CTR_DRBG context, that is
* extracts data from the entropy source.
*
* \note This function is not thread-safe. It is not safe
* to call this function if another thread might be
* concurrently obtaining random numbers from the same
* context or updating or reseeding the same context.
*
* \param ctx The CTR_DRBG context.
* \param additional Additional data to add to the state. Can be \c NULL.
* \param len The length of the additional data.
* This must be less than
* #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - \c entropy_len
* where \c entropy_len is the entropy length
* configured for the context.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure.
*/
int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
const unsigned char *additional, size_t len );
/**
* \brief This function updates the state of the CTR_DRBG context.
*
* \note This function is not thread-safe. It is not safe
* to call this function if another thread might be
* concurrently obtaining random numbers from the same
* context or updating or reseeding the same context.
*
* \param ctx The CTR_DRBG context.
* \param additional The data to update the state with. This must not be
* \c NULL unless \p add_len is \c 0.
* \param add_len Length of \p additional in bytes. This must be at
* most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG if
* \p add_len is more than
* #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT.
* \return An error from the underlying AES cipher on failure.
*/
int mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
const unsigned char *additional,
size_t add_len );
/**
* \brief This function updates a CTR_DRBG instance with additional
* data and uses it to generate random data.
*
* This function automatically reseeds if the reseed counter is exceeded
* or prediction resistance is enabled.
*
* \note This function is not thread-safe. It is not safe
* to call this function if another thread might be
* concurrently obtaining random numbers from the same
* context or updating or reseeding the same context.
*
* \param p_rng The CTR_DRBG context. This must be a pointer to a
* #mbedtls_ctr_drbg_context structure.
* \param output The buffer to fill.
* \param output_len The length of the buffer in bytes.
* \param additional Additional data to update. Can be \c NULL, in which
* case the additional data is empty regardless of
* the value of \p add_len.
* \param add_len The length of the additional data
* if \p additional is not \c NULL.
* This must be less than #MBEDTLS_CTR_DRBG_MAX_INPUT
* and less than
* #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - \c entropy_len
* where \c entropy_len is the entropy length
* configured for the context.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
* #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure.
*/
int mbedtls_ctr_drbg_random_with_add( void *p_rng,
unsigned char *output, size_t output_len,
const unsigned char *additional, size_t add_len );
/**
* \brief This function uses CTR_DRBG to generate random data.
*
* This function automatically reseeds if the reseed counter is exceeded
* or prediction resistance is enabled.
*/
#if defined(MBEDTLS_THREADING_C)
/**
* \note When Mbed TLS is built with threading support,
* it is safe to call mbedtls_ctr_drbg_random()
* from multiple threads. Other operations, including
* reseeding, are not thread-safe.
*/
#endif /* MBEDTLS_THREADING_C */
/**
* \param p_rng The CTR_DRBG context. This must be a pointer to a
* #mbedtls_ctr_drbg_context structure.
* \param output The buffer to fill.
* \param output_len The length of the buffer in bytes.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
* #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure.
*/
int mbedtls_ctr_drbg_random( void *p_rng,
unsigned char *output, size_t output_len );
#if defined(MBEDTLS_FS_IO)
/**
* \brief This function writes a seed file.
*
* \param ctx The CTR_DRBG context.
* \param path The name of the file.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error.
* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on reseed
* failure.
*/
int mbedtls_ctr_drbg_write_seed_file( mbedtls_ctr_drbg_context *ctx, const char *path );
/**
* \brief This function reads and updates a seed file. The seed
* is added to this instance.
*
* \param ctx The CTR_DRBG context.
* \param path The name of the file.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error.
* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on
* reseed failure.
* \return #MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG if the existing
* seed file is too large.
*/
int mbedtls_ctr_drbg_update_seed_file( mbedtls_ctr_drbg_context *ctx, const char *path );
#endif /* MBEDTLS_FS_IO */
#if defined(MBEDTLS_SELF_TEST)
/**
* \brief The CTR_DRBG checkup routine.
*
* \return \c 0 on success.
* \return \c 1 on failure.
*/
int mbedtls_ctr_drbg_self_test( int verbose );
#endif /* MBEDTLS_SELF_TEST */
#ifdef __cplusplus
}
#endif
#endif /* ctr_drbg.h */
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