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CTR_DRBG documentation improvements
* State explicit whether several numbers are in bits or bytes. * Clarify whether buffer pointer parameters can be NULL. * Clarify some terminology. * Minor wording and formatting improvements.
This commit is contained in:
Gilles Peskine
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d28b9b3c5d
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25e1945321
@ -1,13 +1,16 @@
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/**
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* \file ctr_drbg.h
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*
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* \brief CTR_DRBG is based on AES-256, as defined in <em>NIST SP 800-90A:
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* Recommendation for Random Number Generation Using Deterministic
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* Random Bit Generators</em>.
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* \brief The CTR_DRBG pseudorandom generator.
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*
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* CTR_DRBG is a standardized way of building a PRNG from a block-cipher
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* in counter mode operation, as defined in <em>NIST SP 800-90A:
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* Recommendation for Random Number Generation Using Deterministic Random
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* Bit Generators</em>.
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*
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*/
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/*
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* Copyright (C) 2006-2018, Arm Limited (or its affiliates), All Rights Reserved
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* Copyright (C) 2006-2019, Arm Limited (or its affiliates), All Rights Reserved
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may
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@ -92,7 +95,7 @@
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#if !defined(MBEDTLS_CTR_DRBG_MAX_SEED_INPUT)
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#define MBEDTLS_CTR_DRBG_MAX_SEED_INPUT 384
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/**< The maximum size of seed or reseed buffer. */
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/**< The maximum size of seed or reseed buffer in bytes. */
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#endif
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/* \} name SECTION: Module settings */
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@ -150,17 +153,21 @@ void mbedtls_ctr_drbg_init( mbedtls_ctr_drbg_context *ctx );
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* \brief This function seeds and sets up the CTR_DRBG
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* entropy source for future reseeds.
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*
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* \note Personalization data can be provided in addition to the more generic
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* You can provide a personalization string in addition to the
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* entropy source, to make this instantiation as unique as possible.
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*
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*
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* \param ctx The CTR_DRBG context to seed.
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* \param f_entropy The entropy callback, taking as arguments the
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* \p p_entropy context, the buffer to fill, and the
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length of the buffer.
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* \param p_entropy The entropy context.
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* \param custom Personalization data, that is device-specific
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identifiers. Can be NULL.
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* \param len The length of the personalization data.
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* length of the buffer.
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* \param p_entropy The entropy context to pass to \p f_entropy.
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* \param custom The personalization string.
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* This can be \c NULL, in which case the personalization
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* string is empty regardless of the value of \p len.
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* \param len The length of the personalization string.
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* This must be at most
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* #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT / 2.
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*
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* \return \c 0 on success, or
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* #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure.
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@ -183,7 +190,8 @@ void mbedtls_ctr_drbg_free( mbedtls_ctr_drbg_context *ctx );
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* The default value is off.
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*
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* \note If enabled, entropy is gathered at the beginning of
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* every call to mbedtls_ctr_drbg_random_with_add().
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* every call to mbedtls_ctr_drbg_random_with_add()
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* or mbedtls_ctr_drbg_random().
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* Only use this if your entropy source has sufficient
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* throughput.
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*
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@ -199,13 +207,19 @@ void mbedtls_ctr_drbg_set_prediction_resistance( mbedtls_ctr_drbg_context *ctx,
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* #MBEDTLS_CTR_DRBG_ENTROPY_LEN.
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*
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* \param ctx The CTR_DRBG context.
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* \param len The amount of entropy to grab.
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* \param len The amount of entropy to grab, in bytes.
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* This must be at most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT.
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*/
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void mbedtls_ctr_drbg_set_entropy_len( mbedtls_ctr_drbg_context *ctx,
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size_t len );
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/**
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* \brief This function sets the reseed interval.
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*
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* The reseed interval is the number of calls to mbedtls_ctr_drbg_random()
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* or mbedtls_ctr_drbg_random_with_add() after which the entropy function
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* is called again.
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*
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* The default value is #MBEDTLS_CTR_DRBG_RESEED_INTERVAL.
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*
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* \param ctx The CTR_DRBG context.
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@ -219,8 +233,12 @@ void mbedtls_ctr_drbg_set_reseed_interval( mbedtls_ctr_drbg_context *ctx,
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* extracts data from the entropy source.
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*
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* \param ctx The CTR_DRBG context.
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* \param additional Additional data to add to the state. Can be NULL.
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* \param additional Additional data to add to the state. Can be \c NULL.
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* \param len The length of the additional data.
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* This must be less than
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* #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - \c entropy_len
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* where \c entropy_len is the entropy length
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* configured for the context.
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*
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* \return \c 0 on success, or
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* #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure.
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@ -232,7 +250,8 @@ int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
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* \brief This function updates the state of the CTR_DRBG context.
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*
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* \param ctx The CTR_DRBG context.
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* \param additional The data to update the state with.
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* \param additional The data to update the state with. This must not be
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* \c NULL unless \p add_len is \c 0.
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* \param add_len Length of \p additional in bytes. This must be at
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* most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT.
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*
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@ -258,8 +277,10 @@ int mbedtls_ctr_drbg_update_ret( mbedtls_ctr_drbg_context *ctx,
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* The remaining Bytes are silently discarded.
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*
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* \param ctx The CTR_DRBG context.
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* \param additional The data to update the state with.
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* \param add_len Length of \p additional data.
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* \param additional The data to update the state with. This must not be
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* \c NULL unless \p add_len is \c 0.
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* \param add_len Length of \p additional data. This must be at
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* most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT.
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*/
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void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
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const unsigned char *additional,
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@ -269,17 +290,26 @@ void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
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* \brief This function updates a CTR_DRBG instance with additional
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* data and uses it to generate random data.
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*
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* \note The function automatically reseeds if the reseed counter is exceeded.
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* This function automatically reseeds if the reseed counter is exceeded
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* or prediction resistance is enabled.
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*
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* \param p_rng The CTR_DRBG context. This must be a pointer to a
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* #mbedtls_ctr_drbg_context structure.
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* \param output The buffer to fill.
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* \param output_len The length of the buffer.
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* \param additional Additional data to update. Can be NULL.
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* \param add_len The length of the additional data.
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* \param output_len The length of the buffer in bytes.
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* \param additional Additional data to update. Can be \c NULL, in which
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* case the additional data is empty regardless of
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* the value of \p add_len.
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* \param add_len The length of the additional data
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* if \p additional is not \c NULL.
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* This must be less than #MBEDTLS_CTR_DRBG_MAX_INPUT
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* and less than
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* #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - \c entropy_len
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* where \c entropy_len is the entropy length
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* configured for the context.
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*
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* \return \c 0 on success, or
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* #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
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* \return \c 0 on success.
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* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
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* #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure.
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*/
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int mbedtls_ctr_drbg_random_with_add( void *p_rng,
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@ -289,15 +319,17 @@ int mbedtls_ctr_drbg_random_with_add( void *p_rng,
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/**
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* \brief This function uses CTR_DRBG to generate random data.
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*
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* \note The function automatically reseeds if the reseed counter is exceeded.
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* This function automatically reseeds if the reseed counter is exceeded
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* or prediction resistance is enabled.
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*
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*
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* \param p_rng The CTR_DRBG context. This must be a pointer to a
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* #mbedtls_ctr_drbg_context structure.
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* \param output The buffer to fill.
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* \param output_len The length of the buffer.
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* \param output_len The length of the buffer in bytes.
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*
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* \return \c 0 on success, or
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* #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
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* \return \c 0 on success.
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* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
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* #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure.
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*/
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int mbedtls_ctr_drbg_random( void *p_rng,
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@ -310,9 +342,9 @@ int mbedtls_ctr_drbg_random( void *p_rng,
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* \param ctx The CTR_DRBG context.
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* \param path The name of the file.
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*
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* \return \c 0 on success,
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* #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error, or
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* #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on
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* \return \c 0 on success.
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* \return #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error.
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* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on reseed
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* failure.
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*/
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int mbedtls_ctr_drbg_write_seed_file( mbedtls_ctr_drbg_context *ctx, const char *path );
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@ -324,10 +356,12 @@ int mbedtls_ctr_drbg_write_seed_file( mbedtls_ctr_drbg_context *ctx, const char
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* \param ctx The CTR_DRBG context.
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* \param path The name of the file.
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*
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* \return \c 0 on success,
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* #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error,
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* #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
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* #MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG on failure.
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* \return \c 0 on success.
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* \return #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error.
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* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on
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* reseed failure.
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* \return #MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG if the existing
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* seed file is too large.
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*/
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int mbedtls_ctr_drbg_update_seed_file( mbedtls_ctr_drbg_context *ctx, const char *path );
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#endif /* MBEDTLS_FS_IO */
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