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Merge remote-tracking branch 'origin/pr/2878' into mbedtls-2.7

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* origin/pr/2878:
  mbedtls_hmac_drbg_set_entropy_len() only matters when reseeding
  mbedtls_ctr_drbg_set_entropy_len() only matters when reseeding
  mbedtls_ctr_drbg_seed: correct maximum for len
  Add a note about CTR_DRBG security strength to config.h
  CTR_DRBG: more consistent formatting and wording
  DRBG documentation: Relate f_entropy arguments to the entropy module
  Add ChangeLog entry for the DRBG documentation improvements
  HMAC_DRBG documentation improvements
  CTR_DRBG: explain the security strength and the entropy input length
  CTR_DRBG documentation improvements
This commit is contained in:
Jaeden Amero 2019-10-18 14:21:49 +01:00
commit 395d8c1222
4 changed files with 352 additions and 142 deletions
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3
ChangeLog
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@ -5,6 +5,9 @@ mbed TLS ChangeLog (Sorted per branch, date)
Changes Changes
* Add unit tests for AES-GCM when called through mbedtls_cipher_auth_xxx() * Add unit tests for AES-GCM when called through mbedtls_cipher_auth_xxx()
from the cipher abstraction layer. Fixes #2198. 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 = mbed TLS 2.7.12 branch released 2019-09-06

4
include/mbedtls/config.h
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@ -1884,6 +1884,10 @@
* *
* Enable the CTR_DRBG AES-256-based random generator. * 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 * Module: library/ctr_drbg.c
* Caller: * Caller:
* *

210
include/mbedtls/ctr_drbg.h
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@ -1,13 +1,38 @@
/** /**
* \file ctr_drbg.h * \file ctr_drbg.h
* *
* \brief CTR_DRBG is based on AES-256, as defined in <em>NIST SP 800-90A: * \brief The CTR_DRBG pseudorandom generator.
* Recommendation for Random Number Generation Using Deterministic
* Random Bit Generators</em>.
* *
* 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
* 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 * SPDX-License-Identifier: Apache-2.0
* *
* Licensed under the Apache License, Version 2.0 (the "License"); you may * 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_CTR_DRBG_ENTROPY_LEN)
#if defined(MBEDTLS_SHA512_C) && !defined(MBEDTLS_ENTROPY_FORCE_SHA256) #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 #define MBEDTLS_CTR_DRBG_ENTROPY_LEN 48
/**< The amount of entropy used per seed by default:
* <ul><li>48 with SHA-512.</li> #else /* defined(MBEDTLS_SHA512_C) && !defined(MBEDTLS_ENTROPY_FORCE_SHA256) */
* <li>32 with SHA-256.</li></ul>
/** 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 #define MBEDTLS_CTR_DRBG_ENTROPY_LEN 32
/**< Amount of entropy used per seed by default: #endif /* defined(MBEDTLS_SHA512_C) && !defined(MBEDTLS_ENTROPY_FORCE_SHA256) */
* <ul><li>48 with SHA-512.</li> #endif /* !defined(MBEDTLS_CTR_DRBG_ENTROPY_LEN) */
* <li>32 with SHA-256.</li></ul>
*/
#endif
#endif
#if !defined(MBEDTLS_CTR_DRBG_RESEED_INTERVAL) #if !defined(MBEDTLS_CTR_DRBG_RESEED_INTERVAL)
#define MBEDTLS_CTR_DRBG_RESEED_INTERVAL 10000 #define MBEDTLS_CTR_DRBG_RESEED_INTERVAL 10000
@ -92,7 +125,7 @@
#if !defined(MBEDTLS_CTR_DRBG_MAX_SEED_INPUT) #if !defined(MBEDTLS_CTR_DRBG_MAX_SEED_INPUT)
#define MBEDTLS_CTR_DRBG_MAX_SEED_INPUT 384 #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 #endif
/* \} name SECTION: Module settings */ /* \} 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 * \brief This function seeds and sets up the CTR_DRBG
* entropy source for future reseeds. * entropy source for future reseeds.
* *
* \note Personalization data can be provided in addition to the more generic * A typical choice for the \p f_entropy and \p p_entropy parameters is
* entropy source, to make this instantiation as unique as possible. * 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 ctx The CTR_DRBG context to seed.
* \param f_entropy The entropy callback, taking as arguments the * \param f_entropy The entropy callback, taking as arguments the
* \p p_entropy context, the buffer to fill, and the * \p p_entropy context, the buffer to fill, and the
length of the buffer. * length of the buffer.
* \param p_entropy The entropy context. * \param p_entropy The entropy context to pass to \p f_entropy.
* \param custom Personalization data, that is device-specific * \param custom The personalization string.
identifiers. Can be NULL. * This can be \c NULL, in which case the personalization
* \param len The length of the personalization data. * 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 * \return \c 0 on success, or
* #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure. * #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. * The default value is off.
* *
* \note If enabled, entropy is gathered at the beginning of * \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 * Only use this if your entropy source has sufficient
* throughput. * 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 * \brief This function sets the amount of entropy grabbed on each
* seed or reseed. The default value is * subsequent reseed.
* #MBEDTLS_CTR_DRBG_ENTROPY_LEN. *
* 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 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, void mbedtls_ctr_drbg_set_entropy_len( mbedtls_ctr_drbg_context *ctx,
size_t len ); size_t len );
/** /**
* \brief This function sets the reseed interval. * \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 ctx The CTR_DRBG context.
* \param interval The reseed interval. * \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. * extracts data from the entropy source.
* *
* \param ctx The CTR_DRBG context. * \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. * \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 * \return \c 0 on success, or
* #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure. * #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. * \brief This function updates the state of the CTR_DRBG context.
* *
* \param ctx 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 * \param add_len Length of \p additional in bytes. This must be at
* most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT. * 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. * The remaining Bytes are silently discarded.
* *
* \param ctx 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
* \param add_len Length of \p additional data. * \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, void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
const unsigned char *additional, 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 * \brief This function updates a CTR_DRBG instance with additional
* data and uses it to generate random data. * 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 * \param p_rng The CTR_DRBG context. This must be a pointer to a
* #mbedtls_ctr_drbg_context structure. * #mbedtls_ctr_drbg_context structure.
* \param output The buffer to fill. * \param output The buffer to fill.
* \param output_len The length of the buffer. * \param output_len The length of the buffer in bytes.
* \param additional Additional data to update. Can be NULL. * \param additional Additional data to update. Can be \c NULL, in which
* \param add_len The length of the additional data. * 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 * \return \c 0 on success.
* #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or * \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
* #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure. * #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure.
*/ */
int mbedtls_ctr_drbg_random_with_add( void *p_rng, 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. * \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 * \param p_rng The CTR_DRBG context. This must be a pointer to a
* #mbedtls_ctr_drbg_context structure. * #mbedtls_ctr_drbg_context structure.
* \param output The buffer to fill. * \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 * \return \c 0 on success.
* #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or * \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
* #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure. * #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure.
*/ */
int mbedtls_ctr_drbg_random( void *p_rng, 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 ctx The CTR_DRBG context.
* \param path The name of the file. * \param path The name of the file.
* *
* \return \c 0 on success, * \return \c 0 on success.
* #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error, or * \return #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error.
* #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on * \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on reseed
* failure. * failure.
*/ */
int mbedtls_ctr_drbg_write_seed_file( mbedtls_ctr_drbg_context *ctx, const char *path ); 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 ctx The CTR_DRBG context.
* \param path The name of the file. * \param path The name of the file.
* *
* \return \c 0 on success, * \return \c 0 on success.
* #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error, * \return #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error.
* #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or * \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on
* #MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG on failure. * 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 ); int mbedtls_ctr_drbg_update_seed_file( mbedtls_ctr_drbg_context *ctx, const char *path );
#endif /* MBEDTLS_FS_IO */ #endif /* MBEDTLS_FS_IO */

277
include/mbedtls/hmac_drbg.h
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@ -1,10 +1,14 @@
/** /**
* \file hmac_drbg.h * \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 <em>NIST SP 800-90A: Recommendation for Random Number Generation Using
* Deterministic Random Bit Generators</em>.
*/ */
/* /*
* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved * Copyright (C) 2006-2019, ARM Limited, All Rights Reserved
* SPDX-License-Identifier: Apache-2.0 * SPDX-License-Identifier: Apache-2.0
* *
* Licensed under the Apache License, Version 2.0 (the "License"); you may * Licensed under the Apache License, Version 2.0 (the "License"); you may
@ -104,38 +108,74 @@ typedef struct
} mbedtls_hmac_drbg_context; } mbedtls_hmac_drbg_context;
/** /**
* \brief HMAC_DRBG context initialization * \brief HMAC_DRBG context initialization.
* 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 * 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 ); void mbedtls_hmac_drbg_init( mbedtls_hmac_drbg_context *ctx );
/** /**
* \brief HMAC_DRBG initial seeding * \brief HMAC_DRBG initial seeding.
* Seed and setup entropy source for future reseeds.
* *
* \param ctx HMAC_DRBG context to be seeded * Set the initial seed and set up the entropy source for future reseeds.
* \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
* *
* \note The "security strength" as defined by NIST is set to: * A typical choice for the \p f_entropy and \p p_entropy parameters is
* 128 bits if md_alg is SHA-1, * to use the entropy module:
* 192 bits if md_alg is SHA-224, * - \p f_entropy is mbedtls_entropy_func();
* 256 bits if md_alg is SHA-256 or higher. * - \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. * 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 * \note The entropy length for the initial seeding is
* MBEDTLS_ERR_MD_BAD_INPUT_DATA, or * the security strength (converted from bits to bytes).
* MBEDTLS_ERR_MD_ALLOC_FAILED, or * You can set a different entropy length for subsequent
* MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED. * 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, int mbedtls_hmac_drbg_seed( mbedtls_hmac_drbg_context *ctx,
const mbedtls_md_info_t * md_info, 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). * \brief Initilisation of simpified HMAC_DRBG (never reseeds).
* (For use with deterministic ECDSA.)
* *
* \param ctx HMAC_DRBG context to be initialised * This function is meant for use in algorithms that need a pseudorandom
* \param md_info MD algorithm to use for HMAC_DRBG * input such as deterministic ECDSA.
* \param data Concatenation of entropy string and additional data
* \param data_len Length of data in bytes
* *
* \return 0 if successful, or * \param ctx HMAC_DRBG context to be initialised.
* MBEDTLS_ERR_MD_BAD_INPUT_DATA, or * \param md_info MD algorithm to use for HMAC_DRBG.
* MBEDTLS_ERR_MD_ALLOC_FAILED. * \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, int mbedtls_hmac_drbg_seed_buf( mbedtls_hmac_drbg_context *ctx,
const mbedtls_md_info_t * md_info, const mbedtls_md_info_t * md_info,
const unsigned char *data, size_t data_len ); 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! * \note If enabled, entropy is gathered at the beginning of
* Only use this if you have ample supply of good entropy! * 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 ctx The HMAC_DRBG context.
* \param resistance MBEDTLS_HMAC_DRBG_PR_ON or MBEDTLS_HMAC_DRBG_PR_OFF * \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, void mbedtls_hmac_drbg_set_prediction_resistance( mbedtls_hmac_drbg_context *ctx,
int resistance ); int resistance );
/** /**
* \brief Set the amount of entropy grabbed on each reseed * \brief This function sets the amount of entropy grabbed on each
* (Default: given by the security strength, which * reseed.
* depends on the hash used, see \c mbedtls_hmac_drbg_init() )
* *
* \param ctx HMAC_DRBG context * The default value is set by mbedtls_hmac_drbg_seed().
* \param len Amount of entropy to grab, in bytes *
* \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, void mbedtls_hmac_drbg_set_entropy_len( mbedtls_hmac_drbg_context *ctx,
size_t len ); size_t len );
/** /**
* \brief Set the reseed interval * \brief Set the reseed interval.
* (Default: MBEDTLS_HMAC_DRBG_RESEED_INTERVAL)
* *
* \param ctx HMAC_DRBG context * The reseed interval is the number of calls to mbedtls_hmac_drbg_random()
* \param interval Reseed interval * 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, void mbedtls_hmac_drbg_set_reseed_interval( mbedtls_hmac_drbg_context *ctx,
int interval ); int interval );
/** /**
* \brief HMAC_DRBG update state * \brief This function updates the state of the HMAC_DRBG context.
* *
* \param ctx HMAC_DRBG context * \param ctx The HMAC_DRBG context.
* \param additional Additional data to update state with, or NULL * \param additional The data to update the state with.
* \param add_len Length of additional data, or 0 * 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 * \return \c 0 on success, or an error from the underlying
* hash calculation. * 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, int mbedtls_hmac_drbg_update_ret( mbedtls_hmac_drbg_context *ctx,
const unsigned char *additional, size_t add_len ); 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 ); 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 ctx The HMAC_DRBG context.
* \param additional Additional data to add to state (Can be NULL) * \param additional Additional data to add to the state.
* \param len Length of additional data * 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 * \return \c 0 if successful.
* MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED * \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, int mbedtls_hmac_drbg_reseed( mbedtls_hmac_drbg_context *ctx,
const unsigned char *additional, size_t len ); 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 p_rng The HMAC_DRBG context. This must be a pointer to a
* \param output Buffer to fill * #mbedtls_hmac_drbg_context structure.
* \param output_len Length of the buffer * \param output The buffer to fill.
* \param additional Additional data to update with (can be NULL) * \param output_len The length of the buffer in bytes.
* \param add_len Length of additional data (can be 0) * 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 * \return \c 0 if successful.
* MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED, or * \return #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
* MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG, or * if a call to the entropy source failed.
* MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG. * \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, int mbedtls_hmac_drbg_random_with_add( void *p_rng,
unsigned char *output, size_t output_len, 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 ); 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 p_rng The HMAC_DRBG context. This must be a pointer to a
* \param output Buffer to fill * #mbedtls_hmac_drbg_context structure.
* \param out_len Length of the buffer * \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 * \return \c 0 if successful.
* MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED, or * \return #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
* MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG * 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 ); int mbedtls_hmac_drbg_random( void *p_rng, unsigned char *output, size_t out_len );
/** /**
* \brief Free an HMAC_DRBG context * \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 ); void mbedtls_hmac_drbg_free( mbedtls_hmac_drbg_context *ctx );
#if defined(MBEDTLS_FS_IO) #if defined(MBEDTLS_FS_IO)
/** /**
* \brief Write a seed file * \brief This function writes a seed file.
* *
* \param ctx HMAC_DRBG context * \param ctx The HMAC_DRBG context.
* \param path Name of the file * \param path The name of the file.
* *
* \return 0 if successful, 1 on file error, or * \return \c 0 on success.
* MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED * \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 ); 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 * \brief This function reads and updates a seed file. The seed
* instance * is added to this instance.
* *
* \param ctx HMAC_DRBG context * \param ctx The HMAC_DRBG context.
* \param path Name of the file * \param path The name of the file.
* *
* \return 0 if successful, 1 on file error, * \return \c 0 on success.
* MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED or * \return #MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR on file error.
* MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG * \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 ); int mbedtls_hmac_drbg_update_seed_file( mbedtls_hmac_drbg_context *ctx, const char *path );
#endif /* MBEDTLS_FS_IO */ #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) #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 ); int mbedtls_hmac_drbg_self_test( int verbose );
#endif #endif