diff --git a/ChangeLog b/ChangeLog index 4f86ee9be..16982a0e0 100644 --- a/ChangeLog +++ b/ChangeLog @@ -5,6 +5,9 @@ mbed TLS ChangeLog (Sorted per branch, date) Changes * Add unit tests for AES-GCM when called through mbedtls_cipher_auth_xxx() from the cipher abstraction layer. Fixes #2198. + * Clarify how the interface of the CTR_DRBG and HMAC modules relates to + NIST SP 800-90A. In particular CTR_DRBG requires an explicit nonce + to achieve a 256-bit strength if MBEDTLS_ENTROPY_FORCE_SHA256 is set. = mbed TLS 2.7.12 branch released 2019-09-06 diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h index fa88ebf01..0bc08cca4 100644 --- a/include/mbedtls/config.h +++ b/include/mbedtls/config.h @@ -1884,6 +1884,10 @@ * * Enable the CTR_DRBG AES-256-based random generator. * + * \note This module only achieves a 256-bit security strength if + * the generator is seeded with sufficient entropy. + * See ctr_drbg.h for more details. + * * Module: library/ctr_drbg.c * Caller: * diff --git a/include/mbedtls/ctr_drbg.h b/include/mbedtls/ctr_drbg.h index 5a3284315..8963c7423 100644 --- a/include/mbedtls/ctr_drbg.h +++ b/include/mbedtls/ctr_drbg.h @@ -1,13 +1,38 @@ /** * \file ctr_drbg.h * - * \brief CTR_DRBG is based on AES-256, as defined in NIST SP 800-90A: - * Recommendation for Random Number Generation Using Deterministic - * Random Bit Generators. + * \brief 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 NIST SP 800-90A: + * Recommendation for Random Number Generation Using Deterministic Random + * Bit Generators. + * + * The Mbed TLS implementation of CTR_DRBG uses AES-256 + * as the underlying block cipher, with a derivation function. + * The initial seeding grabs #MBEDTLS_CTR_DRBG_ENTROPY_LEN bytes of entropy. + * See the documentation of mbedtls_ctr_drbg_seed() for more details. + * + * Based on NIST SP 800-90A §10.2.1 table 3 and NIST SP 800-57 part 1 table 2, + * here are the security strengths achieved in typical configuration: + * - 256 bits under the default configuration of the library, + * with #MBEDTLS_CTR_DRBG_ENTROPY_LEN set to 48 or more. + * - 256 bits if #MBEDTLS_CTR_DRBG_ENTROPY_LEN is set + * to 32 or more and the DRBG is initialized with an explicit + * nonce in the \c custom parameter to mbedtls_ctr_drbg_seed(). + * - 128 bits if #MBEDTLS_CTR_DRBG_ENTROPY_LEN is + * between 24 and 47 and the DRBG is not initialized with an explicit + * nonce (see mbedtls_ctr_drbg_seed()). + * + * Note that the value of #MBEDTLS_CTR_DRBG_ENTROPY_LEN defaults to: + * - \c 48 if the module \c MBEDTLS_SHA512_C is enabled and the symbol + * \c MBEDTLS_ENTROPY_FORCE_SHA256 is not enabled at compile time. + * This is the default configuration of the library. + * - \c 32 if the module \c MBEDTLS_SHA512_C is disabled at compile time. + * - \c 32 if \c MBEDTLS_ENTROPY_FORCE_SHA256 is enabled at compile time. */ /* - * Copyright (C) 2006-2018, Arm Limited (or its affiliates), All Rights Reserved + * Copyright (C) 2006-2019, Arm Limited (or its affiliates), All Rights Reserved * SPDX-License-Identifier: Apache-2.0 * * Licensed under the Apache License, Version 2.0 (the "License"); you may @@ -59,21 +84,29 @@ * \{ */ +/** \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 not set). + */ #define MBEDTLS_CTR_DRBG_ENTROPY_LEN 48 -/**< The amount of entropy used per seed by default: - * + +#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). + * + * \warning To achieve a 256-bit security strength, you must pass a nonce + * to mbedtls_ctr_drbg_seed(). */ -#else #define MBEDTLS_CTR_DRBG_ENTROPY_LEN 32 -/**< Amount of entropy used per seed by default: - * - */ -#endif -#endif +#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 @@ -92,7 +125,7 @@ #if !defined(MBEDTLS_CTR_DRBG_MAX_SEED_INPUT) #define MBEDTLS_CTR_DRBG_MAX_SEED_INPUT 384 -/**< The maximum size of seed or reseed buffer. */ +/**< The maximum size of seed or reseed buffer in bytes. */ #endif /* \} name SECTION: Module settings */ @@ -150,17 +183,61 @@ 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. * - * \note Personalization data can be provided in addition to the more generic - * entropy source, to make this instantiation as unique as possible. + * 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). * + * \p f_entropy is always called with a buffer size equal to the entropy + * length. The entropy length is initially #MBEDTLS_CTR_DRBG_ENTROPY_LEN + * and this value is always used for the initial seeding. You can change + * the entropy length for subsequent seeding by calling + * mbedtls_ctr_drbg_set_entropy_len() after this function. + * + * You can provide a personalization string in addition to the + * entropy source, to make this instantiation as unique as possible. + * + * \note 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 string obtained from + * calling \p f_entropy and the \p custom string. + * The origin of the nonce depends on the value of + * the entropy length relative to the security strength. + * - If the entropy length is at least 1.5 times the + * security strength then the nonce is taken from the + * string obtained with \p f_entropy. + * - If the entropy length is less than the security + * strength, then the nonce is taken from \p custom. + * In this case, for compliance with SP 800-90A, + * you must pass a unique value of \p custom at + * each invocation. See SP 800-90A §8.6.7 for more + * details. + */ +#if MBEDTLS_CTR_DRBG_ENTROPY_LEN < MBEDTLS_CTR_DRBG_KEYSIZE * 3 / 2 +/** \warning When #MBEDTLS_CTR_DRBG_ENTROPY_LEN is less than + * 48, to achieve a 256-bit security strength, + * you must pass a value of \p custom that is a nonce: + * this value must never be repeated in subsequent + * runs of the same application or on a different + * device. + */ +#endif +/** * \param ctx The CTR_DRBG context to seed. * \param f_entropy The entropy callback, taking as arguments the * \p p_entropy context, the buffer to fill, and the - length of the buffer. - * \param p_entropy The entropy context. - * \param custom Personalization data, that is device-specific - identifiers. Can be NULL. - * \param len The length of the personalization data. + * length of the buffer. + * \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, or * #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure. @@ -183,7 +260,8 @@ void mbedtls_ctr_drbg_free( mbedtls_ctr_drbg_context *ctx ); * The default value is off. * * \note If enabled, entropy is gathered at the beginning of - * every call to mbedtls_ctr_drbg_random_with_add(). + * every call to mbedtls_ctr_drbg_random_with_add() + * or mbedtls_ctr_drbg_random(). * Only use this if your entropy source has sufficient * throughput. * @@ -195,18 +273,34 @@ void mbedtls_ctr_drbg_set_prediction_resistance( mbedtls_ctr_drbg_context *ctx, /** * \brief This function sets the amount of entropy grabbed on each - * seed or reseed. The default value is - * #MBEDTLS_CTR_DRBG_ENTROPY_LEN. + * subsequent reseed. + * + * The default value is #MBEDTLS_CTR_DRBG_ENTROPY_LEN. + * + * \note mbedtls_ctr_drbg_seed() always sets the entropy length + * to #MBEDTLS_CTR_DRBG_ENTROPY_LEN, so this function + * only has an effect when it is called after + * mbedtls_ctr_drbg_seed(). + * + * \note The security strength of CTR_DRBG is bounded by the + * entropy length. Thus \p len must be at least + * 32 (in bytes) to achieve a 256-bit strength. * * \param ctx The CTR_DRBG context. - * \param len The amount of entropy to grab. + * \param len The amount of entropy to grab, in bytes. + * This must be at most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT. */ void mbedtls_ctr_drbg_set_entropy_len( mbedtls_ctr_drbg_context *ctx, size_t len ); /** * \brief This function sets the reseed interval. - * The default value is #MBEDTLS_CTR_DRBG_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. @@ -219,8 +313,12 @@ void mbedtls_ctr_drbg_set_reseed_interval( mbedtls_ctr_drbg_context *ctx, * extracts data from the entropy source. * * \param ctx The CTR_DRBG context. - * \param additional Additional data to add to the state. Can be NULL. + * \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, or * #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure. @@ -232,7 +330,8 @@ int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx, * \brief This function updates the state of the CTR_DRBG context. * * \param ctx The CTR_DRBG context. - * \param additional The data to update the state with. + * \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. * @@ -258,8 +357,10 @@ int mbedtls_ctr_drbg_update_ret( mbedtls_ctr_drbg_context *ctx, * The remaining Bytes are silently discarded. * * \param ctx The CTR_DRBG context. - * \param additional The data to update the state with. - * \param add_len Length of \p additional data. + * \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 data. This must be at + * most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT. */ void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx, const unsigned char *additional, @@ -269,17 +370,26 @@ void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx, * \brief This function updates a CTR_DRBG instance with additional * data and uses it to generate random data. * - * \note The function automatically reseeds if the reseed counter is exceeded. + * This function automatically reseeds if the reseed counter is exceeded + * or prediction resistance is enabled. * * \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. - * \param additional Additional data to update. Can be NULL. - * \param add_len The length of the additional data. + * \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, or - * #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or + * \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, @@ -289,15 +399,17 @@ int mbedtls_ctr_drbg_random_with_add( void *p_rng, /** * \brief This function uses CTR_DRBG to generate random data. * - * \note The function automatically reseeds if the reseed counter is exceeded. + * This function automatically reseeds if the reseed counter is exceeded + * or prediction resistance is enabled. + * * * \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. + * \param output_len The length of the buffer in bytes. * - * \return \c 0 on success, or - * #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or + * \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, @@ -310,9 +422,9 @@ int mbedtls_ctr_drbg_random( void *p_rng, * \param ctx The CTR_DRBG context. * \param path The name of the file. * - * \return \c 0 on success, - * #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error, or - * #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on + * \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 ); @@ -324,10 +436,12 @@ int mbedtls_ctr_drbg_write_seed_file( mbedtls_ctr_drbg_context *ctx, const char * \param ctx The CTR_DRBG context. * \param path The name of the file. * - * \return \c 0 on success, - * #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error, - * #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or - * #MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG on failure. + * \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 */ diff --git a/include/mbedtls/hmac_drbg.h b/include/mbedtls/hmac_drbg.h index bd05da33c..a46b28726 100644 --- a/include/mbedtls/hmac_drbg.h +++ b/include/mbedtls/hmac_drbg.h @@ -1,10 +1,14 @@ /** * \file hmac_drbg.h * - * \brief HMAC_DRBG (NIST SP 800-90A) + * \brief The HMAC_DRBG pseudorandom generator. + * + * This module implements the HMAC_DRBG pseudorandom generator described + * in NIST SP 800-90A: Recommendation for Random Number Generation Using + * Deterministic Random Bit Generators. */ /* - * Copyright (C) 2006-2015, ARM Limited, All Rights Reserved + * Copyright (C) 2006-2019, ARM Limited, All Rights Reserved * SPDX-License-Identifier: Apache-2.0 * * Licensed under the Apache License, Version 2.0 (the "License"); you may @@ -104,38 +108,74 @@ typedef struct } mbedtls_hmac_drbg_context; /** - * \brief HMAC_DRBG context initialization - * Makes the context ready for mbedtls_hmac_drbg_seed(), - * mbedtls_hmac_drbg_seed_buf() or - * mbedtls_hmac_drbg_free(). + * \brief HMAC_DRBG context initialization. * - * \param ctx HMAC_DRBG context to be initialized + * This function makes the context ready for mbedtls_hmac_drbg_seed(), + * mbedtls_hmac_drbg_seed_buf() or mbedtls_hmac_drbg_free(). + * + * \param ctx HMAC_DRBG context to be initialized. */ void mbedtls_hmac_drbg_init( mbedtls_hmac_drbg_context *ctx ); /** - * \brief HMAC_DRBG initial seeding - * Seed and setup entropy source for future reseeds. + * \brief HMAC_DRBG initial seeding. * - * \param ctx HMAC_DRBG context to be seeded - * \param md_info MD algorithm to use for HMAC_DRBG - * \param f_entropy Entropy callback (p_entropy, buffer to fill, buffer - * length) - * \param p_entropy Entropy context - * \param custom Personalization data (Device specific identifiers) - * (Can be NULL) - * \param len Length of personalization data + * Set the initial seed and set up the entropy source for future reseeds. * - * \note The "security strength" as defined by NIST is set to: - * 128 bits if md_alg is SHA-1, - * 192 bits if md_alg is SHA-224, - * 256 bits if md_alg is SHA-256 or higher. + * 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). + * + * You can provide a personalization string in addition to the + * entropy source, to make this instantiation as unique as possible. + * + * \note By default, the security strength as defined by NIST is: + * - 128 bits if \p md_info is SHA-1; + * - 192 bits if \p md_info is SHA-224; + * - 256 bits if \p md_info is SHA-256, SHA-384 or SHA-512. * Note that SHA-256 is just as efficient as SHA-224. + * The security strength can be reduced if a smaller + * entropy length is set with + * mbedtls_hmac_drbg_set_entropy_len() afterwards. * - * \return 0 if successful, or - * MBEDTLS_ERR_MD_BAD_INPUT_DATA, or - * MBEDTLS_ERR_MD_ALLOC_FAILED, or - * MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED. + * \note The entropy length for the initial seeding is + * the security strength (converted from bits to bytes). + * You can set a different entropy length for subsequent + * seeding by calling mbedtls_hmac_drbg_set_entropy_len() + * after this function. + * + * \note During the initial seeding, this function calls + * the entropy source to obtain a nonce + * whose length is half the entropy length. + * + * \param ctx HMAC_DRBG context to be seeded. + * \param md_info MD algorithm to use for HMAC_DRBG. + * \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 length that is + * 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_HMAC_DRBG_MAX_INPUT + * and also at most + * #MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT - \p entropy_len * 3 / 2 + * where \p entropy_len is the entropy length + * described above. + * + * \return \c 0 if successful. + * \return #MBEDTLS_ERR_MD_BAD_INPUT_DATA if \p md_info is + * invalid. + * \return #MBEDTLS_ERR_MD_ALLOC_FAILED if there was not enough + * memory to allocate context data. + * \return #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED + * if the call to \p f_entropy failed. */ int mbedtls_hmac_drbg_seed( mbedtls_hmac_drbg_context *ctx, const mbedtls_md_info_t * md_info, @@ -146,66 +186,85 @@ int mbedtls_hmac_drbg_seed( mbedtls_hmac_drbg_context *ctx, /** * \brief Initilisation of simpified HMAC_DRBG (never reseeds). - * (For use with deterministic ECDSA.) * - * \param ctx HMAC_DRBG context to be initialised - * \param md_info MD algorithm to use for HMAC_DRBG - * \param data Concatenation of entropy string and additional data - * \param data_len Length of data in bytes + * This function is meant for use in algorithms that need a pseudorandom + * input such as deterministic ECDSA. * - * \return 0 if successful, or - * MBEDTLS_ERR_MD_BAD_INPUT_DATA, or - * MBEDTLS_ERR_MD_ALLOC_FAILED. + * \param ctx HMAC_DRBG context to be initialised. + * \param md_info MD algorithm to use for HMAC_DRBG. + * \param data Concatenation of the initial entropy string and + * the additional data. + * \param data_len Length of \p data in bytes. + * + * \return \c 0 if successful. or + * \return #MBEDTLS_ERR_MD_BAD_INPUT_DATA if \p md_info is + * invalid. + * \return #MBEDTLS_ERR_MD_ALLOC_FAILED if there was not enough + * memory to allocate context data. */ int mbedtls_hmac_drbg_seed_buf( mbedtls_hmac_drbg_context *ctx, const mbedtls_md_info_t * md_info, const unsigned char *data, size_t data_len ); /** - * \brief Enable / disable prediction resistance (Default: Off) + * \brief This function turns prediction resistance on or off. + * The default value is off. * - * Note: If enabled, entropy is used for ctx->entropy_len before each call! - * Only use this if you have ample supply of good entropy! + * \note If enabled, entropy is gathered at the beginning of + * every call to mbedtls_hmac_drbg_random_with_add() + * or mbedtls_hmac_drbg_random(). + * Only use this if your entropy source has sufficient + * throughput. * - * \param ctx HMAC_DRBG context - * \param resistance MBEDTLS_HMAC_DRBG_PR_ON or MBEDTLS_HMAC_DRBG_PR_OFF + * \param ctx The HMAC_DRBG context. + * \param resistance #MBEDTLS_HMAC_DRBG_PR_ON or #MBEDTLS_HMAC_DRBG_PR_OFF. */ void mbedtls_hmac_drbg_set_prediction_resistance( mbedtls_hmac_drbg_context *ctx, int resistance ); /** - * \brief Set the amount of entropy grabbed on each reseed - * (Default: given by the security strength, which - * depends on the hash used, see \c mbedtls_hmac_drbg_init() ) + * \brief This function sets the amount of entropy grabbed on each + * reseed. * - * \param ctx HMAC_DRBG context - * \param len Amount of entropy to grab, in bytes + * The default value is set by mbedtls_hmac_drbg_seed(). + * + * \note mbedtls_hmac_drbg_seed() always sets the entropy length + * to the default value based on the chosen MD algorithm, + * so this function only has an effect if it is called + * after mbedtls_hmac_drbg_seed(). + * + * \param ctx The HMAC_DRBG context. + * \param len The amount of entropy to grab, in bytes. */ void mbedtls_hmac_drbg_set_entropy_len( mbedtls_hmac_drbg_context *ctx, size_t len ); /** - * \brief Set the reseed interval - * (Default: MBEDTLS_HMAC_DRBG_RESEED_INTERVAL) + * \brief Set the reseed interval. * - * \param ctx HMAC_DRBG context - * \param interval Reseed interval + * The reseed interval is the number of calls to mbedtls_hmac_drbg_random() + * or mbedtls_hmac_drbg_random_with_add() after which the entropy function + * is called again. + * + * The default value is #MBEDTLS_HMAC_DRBG_RESEED_INTERVAL. + * + * \param ctx The HMAC_DRBG context. + * \param interval The reseed interval. */ void mbedtls_hmac_drbg_set_reseed_interval( mbedtls_hmac_drbg_context *ctx, int interval ); /** - * \brief HMAC_DRBG update state + * \brief This function updates the state of the HMAC_DRBG context. * - * \param ctx HMAC_DRBG context - * \param additional Additional data to update state with, or NULL - * \param add_len Length of additional data, or 0 + * \param ctx The HMAC_DRBG context. + * \param additional The data to update the state with. + * If this is \c NULL, there is no additional data. + * \param add_len Length of \p additional in bytes. + * Unused if \p additional is \c NULL. * * \return \c 0 on success, or an error from the underlying * hash calculation. - * - * \note Additional data is optional, pass NULL and 0 as second - * third argument if no additional data is being used. */ int mbedtls_hmac_drbg_update_ret( mbedtls_hmac_drbg_context *ctx, const unsigned char *additional, size_t add_len ); @@ -228,33 +287,52 @@ void mbedtls_hmac_drbg_update( mbedtls_hmac_drbg_context *ctx, size_t add_len ); /** - * \brief HMAC_DRBG reseeding (extracts data from entropy source) + * \brief This function reseeds the HMAC_DRBG context, that is + * extracts data from the entropy source. * - * \param ctx HMAC_DRBG context - * \param additional Additional data to add to state (Can be NULL) - * \param len Length of additional data + * \param ctx The HMAC_DRBG context. + * \param additional Additional data to add to the state. + * If this is \c NULL, there is no additional data + * and \p len should be \c 0. + * \param len The length of the additional data. + * This must be at most #MBEDTLS_HMAC_DRBG_MAX_INPUT + * and also at most + * #MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT - \p entropy_len + * where \p entropy_len is the entropy length + * (see mbedtls_hmac_drbg_set_entropy_len()). * - * \return 0 if successful, or - * MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED + * \return \c 0 if successful. + * \return #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED + * if a call to the entropy function failed. */ int mbedtls_hmac_drbg_reseed( mbedtls_hmac_drbg_context *ctx, const unsigned char *additional, size_t len ); /** - * \brief HMAC_DRBG generate random with additional update input + * \brief This function updates an HMAC_DRBG instance with additional + * data and uses it to generate random data. * - * Note: Automatically reseeds if reseed_counter is reached or PR is enabled. + * This function automatically reseeds if the reseed counter is exceeded + * or prediction resistance is enabled. * - * \param p_rng HMAC_DRBG context - * \param output Buffer to fill - * \param output_len Length of the buffer - * \param additional Additional data to update with (can be NULL) - * \param add_len Length of additional data (can be 0) + * \param p_rng The HMAC_DRBG context. This must be a pointer to a + * #mbedtls_hmac_drbg_context structure. + * \param output The buffer to fill. + * \param output_len The length of the buffer in bytes. + * This must be at most #MBEDTLS_HMAC_DRBG_MAX_REQUEST. + * \param additional Additional data to update with. + * If this is \c NULL, there is no additional data + * and \p add_len should be \c 0. + * \param add_len The length of the additional data. + * This must be at most #MBEDTLS_HMAC_DRBG_MAX_INPUT. * - * \return 0 if successful, or - * MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED, or - * MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG, or - * MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG. + * \return \c 0 if successful. + * \return #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED + * if a call to the entropy source failed. + * \return #MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG if + * \p output_len > #MBEDTLS_HMAC_DRBG_MAX_REQUEST. + * \return #MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG if + * \p add_len > #MBEDTLS_HMAC_DRBG_MAX_INPUT. */ int mbedtls_hmac_drbg_random_with_add( void *p_rng, unsigned char *output, size_t output_len, @@ -262,49 +340,59 @@ int mbedtls_hmac_drbg_random_with_add( void *p_rng, size_t add_len ); /** - * \brief HMAC_DRBG generate random + * \brief This function uses HMAC_DRBG to generate random data. * - * Note: Automatically reseeds if reseed_counter is reached or PR is enabled. + * This function automatically reseeds if the reseed counter is exceeded + * or prediction resistance is enabled. * - * \param p_rng HMAC_DRBG context - * \param output Buffer to fill - * \param out_len Length of the buffer + * \param p_rng The HMAC_DRBG context. This must be a pointer to a + * #mbedtls_hmac_drbg_context structure. + * \param output The buffer to fill. + * \param out_len The length of the buffer in bytes. + * This must be at most #MBEDTLS_HMAC_DRBG_MAX_REQUEST. * - * \return 0 if successful, or - * MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED, or - * MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG + * \return \c 0 if successful. + * \return #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED + * if a call to the entropy source failed. + * \return #MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG if + * \p out_len > #MBEDTLS_HMAC_DRBG_MAX_REQUEST. */ int mbedtls_hmac_drbg_random( void *p_rng, unsigned char *output, size_t out_len ); /** * \brief Free an HMAC_DRBG context * - * \param ctx HMAC_DRBG context to free. + * \param ctx The HMAC_DRBG context to free. */ void mbedtls_hmac_drbg_free( mbedtls_hmac_drbg_context *ctx ); #if defined(MBEDTLS_FS_IO) /** - * \brief Write a seed file + * \brief This function writes a seed file. * - * \param ctx HMAC_DRBG context - * \param path Name of the file + * \param ctx The HMAC_DRBG context. + * \param path The name of the file. * - * \return 0 if successful, 1 on file error, or - * MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED + * \return \c 0 on success. + * \return #MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR on file error. + * \return #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED on reseed + * failure. */ int mbedtls_hmac_drbg_write_seed_file( mbedtls_hmac_drbg_context *ctx, const char *path ); /** - * \brief Read and update a seed file. Seed is added to this - * instance + * \brief This function reads and updates a seed file. The seed + * is added to this instance. * - * \param ctx HMAC_DRBG context - * \param path Name of the file + * \param ctx The HMAC_DRBG context. + * \param path The name of the file. * - * \return 0 if successful, 1 on file error, - * MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED or - * MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG + * \return \c 0 on success. + * \return #MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR on file error. + * \return #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED on + * reseed failure. + * \return #MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG if the existing + * seed file is too large. */ int mbedtls_hmac_drbg_update_seed_file( mbedtls_hmac_drbg_context *ctx, const char *path ); #endif /* MBEDTLS_FS_IO */ @@ -312,9 +400,10 @@ int mbedtls_hmac_drbg_update_seed_file( mbedtls_hmac_drbg_context *ctx, const ch #if defined(MBEDTLS_SELF_TEST) /** - * \brief Checkup routine + * \brief The HMAC_DRBG Checkup routine. * - * \return 0 if successful, or 1 if the test failed + * \return \c 0 if successful. + * \return \c 1 if the test failed. */ int mbedtls_hmac_drbg_self_test( int verbose ); #endif