/** * \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 OR GPL-2.0-or-later */ #ifndef MBEDTLS_CTR_DRBG_H #define MBEDTLS_CTR_DRBG_H #include "mbedtls/private_access.h" #include "mbedtls/build_info.h" /* The CTR_DRBG implementation can either directly call the low-level AES * module (gated by MBEDTLS_AES_C) or call the PSA API to perform AES * operations. Calling the AES module directly is the default, both for * maximum backward compatibility and because it's a bit more efficient * (less glue code). * * When MBEDTLS_AES_C is disabled, the CTR_DRBG module calls PSA crypto and * thus benefits from the PSA AES accelerator driver. * It is technically possible to enable MBEDTLS_CTR_DRBG_USE_PSA_CRYPTO * to use PSA even when MBEDTLS_AES_C is enabled, but there is very little * reason to do so other than testing purposes and this is not officially * supported. */ #if !defined(MBEDTLS_AES_C) #define MBEDTLS_CTR_DRBG_USE_PSA_CRYPTO #endif #if defined(MBEDTLS_CTR_DRBG_USE_PSA_CRYPTO) #include "psa/crypto.h" #else #include "mbedtls/aes.h" #endif #include "entropy.h" #if defined(MBEDTLS_THREADING_C) #include "mbedtls/threading.h" #endif /** The entropy source failed. */ #define MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED … /** The requested random buffer length is too big. */ #define MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG … /** The input (entropy + additional data) is too large. */ #define MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG … /** Read or write error in file. */ #define MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR … #define MBEDTLS_CTR_DRBG_BLOCKSIZE … #if defined(MBEDTLS_CTR_DRBG_USE_128_BIT_KEY) #define MBEDTLS_CTR_DRBG_KEYSIZE … /**< 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 … /**< 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 … #define MBEDTLS_CTR_DRBG_SEEDLEN … /** * \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_ENTROPY_SHA512_ACCUMULATOR) /** This is 48 bytes because the entropy module uses SHA-512. */ #define MBEDTLS_CTR_DRBG_ENTROPY_LEN … #else /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */ /** This is 32 bytes because the entropy module uses SHA-256. */ #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 … #endif /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */ #endif /* !defined(MBEDTLS_CTR_DRBG_ENTROPY_LEN) */ #if !defined(MBEDTLS_CTR_DRBG_RESEED_INTERVAL) #define MBEDTLS_CTR_DRBG_RESEED_INTERVAL … /**< The interval before reseed is performed by default. */ #endif #if !defined(MBEDTLS_CTR_DRBG_MAX_INPUT) #define MBEDTLS_CTR_DRBG_MAX_INPUT … /**< The maximum number of additional input Bytes. */ #endif #if !defined(MBEDTLS_CTR_DRBG_MAX_REQUEST) #define MBEDTLS_CTR_DRBG_MAX_REQUEST … /**< The maximum number of requested Bytes per call. */ #endif #if !defined(MBEDTLS_CTR_DRBG_MAX_SEED_INPUT) #define MBEDTLS_CTR_DRBG_MAX_SEED_INPUT … /**< The maximum size of seed or reseed buffer in bytes. */ #endif /** \} name SECTION: Module settings */ #define MBEDTLS_CTR_DRBG_PR_OFF … /**< Prediction resistance is disabled. */ #define MBEDTLS_CTR_DRBG_PR_ON … /**< 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 … #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 … #endif #if defined(MBEDTLS_CTR_DRBG_USE_PSA_CRYPTO) typedef struct mbedtls_ctr_drbg_psa_context { mbedtls_svc_key_id_t key_id; psa_cipher_operation_t operation; } mbedtls_ctr_drbg_psa_context; #endif /** * \brief The CTR_DRBG context structure. */ 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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