diff --git a/ChangeLog b/ChangeLog
index 59797bd2f..c92e42953 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -10,6 +10,9 @@ Bugfix
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 2.16.3 branch released 2019-09-06
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 5df962ef6..834cced87 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -689,6 +689,13 @@
#define MBEDTLS_CIPHER_PADDING_ZEROS_AND_LEN
#define MBEDTLS_CIPHER_PADDING_ZEROS
+/** \def MBEDTLS_CTR_DRBG_USE_128_BIT_KEY
+ *
+ * Uncomment this macro to use a 128-bit key in the CTR_DRBG module.
+ * By default, CTR_DRBG uses a 256-bit key.
+ */
+//#define MBEDTLS_CTR_DRBG_USE_128_BIT_KEY
+
/**
* \def MBEDTLS_ENABLE_WEAK_CIPHERSUITES
*
@@ -2149,7 +2156,11 @@
*
* Enable the CTR_DRBG AES-based random generator.
* The CTR_DRBG generator uses AES-256 by default.
- * To use AES-128 instead, enable MBEDTLS_CTR_DRBG_USE_128_BIT_KEY below.
+ * To use AES-128 instead, enable \c MBEDTLS_CTR_DRBG_USE_128_BIT_KEY above.
+ *
+ * \note To achieve a 256-bit security strength with CTR_DRBG,
+ * you must use AES-256 *and* use sufficient entropy.
+ * See ctr_drbg.h for more details.
*
* Module: library/ctr_drbg.c
* Caller:
@@ -3041,7 +3052,6 @@
//#define MBEDTLS_CTR_DRBG_MAX_INPUT 256 /**< Maximum number of additional input bytes */
//#define MBEDTLS_CTR_DRBG_MAX_REQUEST 1024 /**< Maximum number of requested bytes per call */
//#define MBEDTLS_CTR_DRBG_MAX_SEED_INPUT 384 /**< Maximum size of (re)seed buffer */
-//#define MBEDTLS_CTR_DRBG_USE_128_BIT_KEY /**< Use 128-bit key for CTR_DRBG - may reduce security (see ctr_drbg.h) */
/* HMAC_DRBG options */
//#define MBEDTLS_HMAC_DRBG_RESEED_INTERVAL 10000 /**< Interval before reseed is performed by default */
diff --git a/include/mbedtls/ctr_drbg.h b/include/mbedtls/ctr_drbg.h
index cc3df7b11..766e64701 100644
--- a/include/mbedtls/ctr_drbg.h
+++ b/include/mbedtls/ctr_drbg.h
@@ -1,7 +1,8 @@
/**
* \file ctr_drbg.h
*
- * \brief This file contains CTR_DRBG definitions and functions.
+ * \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 NIST SP 800-90A:
@@ -9,13 +10,35 @@
* Bit Generators.
*
* The Mbed TLS implementation of CTR_DRBG uses AES-256 (default) or AES-128
- * as the underlying block cipher.
+ * (if \c MBEDTLS_CTR_DRBG_USE_128_BIT_KEY is enabled at compile time)
+ * 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.
*
- * \warning Using 128-bit keys for CTR_DRBG limits the security of generated
- * keys and operations that use random values generated to 128-bit security.
+ * 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 AES-256
+ * and with #MBEDTLS_CTR_DRBG_ENTROPY_LEN set to 48 or more.
+ * - 256 bits if AES-256 is used, #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 AES-256 is used but #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()).
+ * - 128 bits if AES-128 is used (\c MBEDTLS_CTR_DRBG_USE_128_BIT_KEY enabled)
+ * and #MBEDTLS_CTR_DRBG_ENTROPY_LEN is set to 24 or more (which is
+ * always the case unless it is explicitly set to a different value
+ * in config.h).
+ *
+ * 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 disabled 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
@@ -56,9 +79,19 @@
#define MBEDTLS_CTR_DRBG_BLOCKSIZE 16 /**< The block size used by the cipher. */
#if defined(MBEDTLS_CTR_DRBG_USE_128_BIT_KEY)
-#define MBEDTLS_CTR_DRBG_KEYSIZE 16 /**< The key size used by the cipher (compile-time choice: 128 bits). */
+#define MBEDTLS_CTR_DRBG_KEYSIZE 16
+/**< The key size in bytes used by the cipher.
+ *
+ * Compile-time choice: 16 bytes (128 bits)
+ * because #MBEDTLS_CTR_DRBG_USE_128_BIT_KEY is enabled.
+ */
#else
-#define MBEDTLS_CTR_DRBG_KEYSIZE 32 /**< The key size used by the cipher (compile-time choice: 256 bits). */
+#define MBEDTLS_CTR_DRBG_KEYSIZE 32
+/**< The key size in bytes used by the cipher.
+ *
+ * Compile-time choice: 32 bytes (256 bits)
+ * because \c MBEDTLS_CTR_DRBG_USE_128_BIT_KEY is disabled.
+ */
#endif
#define MBEDTLS_CTR_DRBG_KEYBITS ( MBEDTLS_CTR_DRBG_KEYSIZE * 8 ) /**< The key size for the DRBG operation, in bits. */
@@ -73,21 +106,31 @@
* \{
*/
+/** \def MBEDTLS_CTR_DRBG_ENTROPY_LEN
+ *
+ * \brief The amount of entropy used per seed by default, in bytes.
+ */
#if !defined(MBEDTLS_CTR_DRBG_ENTROPY_LEN)
#if defined(MBEDTLS_SHA512_C) && !defined(MBEDTLS_ENTROPY_FORCE_SHA256)
+/** This is 48 bytes because the entropy module uses SHA-512
+ * (\c MBEDTLS_ENTROPY_FORCE_SHA256 is disabled).
+ */
#define MBEDTLS_CTR_DRBG_ENTROPY_LEN 48
-/**< The amount of entropy used per seed by default:
- * - 48 with SHA-512.
- * - 32 with SHA-256.
+
+#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).
*/
-#else
+#if !defined(MBEDTLS_CTR_DRBG_USE_128_BIT_KEY)
+/** \warning To achieve a 256-bit security strength, you must pass a nonce
+ * to mbedtls_ctr_drbg_seed().
+ */
+#endif /* !defined(MBEDTLS_CTR_DRBG_USE_128_BIT_KEY) */
#define MBEDTLS_CTR_DRBG_ENTROPY_LEN 32
-/**< Amount of entropy used per seed by default:
- * - 48 with SHA-512.
- * - 32 with SHA-256.
- */
-#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
@@ -106,7 +149,7 @@
#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 */
@@ -164,17 +207,62 @@ 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
+ * #MBEDTLS_CTR_DRBG_KEYSIZE * 3 / 2, to achieve the
+ * maximum security strength permitted by CTR_DRBG,
+ * 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.
* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure.
@@ -197,7 +285,8 @@ 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.
*
@@ -209,18 +298,42 @@ 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:
+ * - 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.
+ * \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.
@@ -233,8 +346,12 @@ 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.
* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure.
@@ -246,7 +363,8 @@ 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.
*
@@ -264,14 +382,23 @@ int mbedtls_ctr_drbg_update_ret( 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.
* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
@@ -284,12 +411,14 @@ 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.
* \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
@@ -336,7 +465,7 @@ MBEDTLS_DEPRECATED void mbedtls_ctr_drbg_update(
*
* \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
+ * \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 );
@@ -350,8 +479,10 @@ int mbedtls_ctr_drbg_write_seed_file( mbedtls_ctr_drbg_context *ctx, const char
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error.
- * \return #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
- * #MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG on failure.
+ * \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 f1289cb30..20b29d981 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
} 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,
@@ -146,98 +186,136 @@ 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 );
/**
- * \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,
@@ -245,24 +323,29 @@ 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 );
@@ -273,17 +356,16 @@ void mbedtls_hmac_drbg_free( mbedtls_hmac_drbg_context *ctx );
#define MBEDTLS_DEPRECATED
#endif
/**
- * \brief HMAC_DRBG update state
+ * \brief This function updates the state of the HMAC_DRBG context.
*
* \deprecated Superseded by mbedtls_hmac_drbg_update_ret()
* in 2.16.0.
*
- * \param ctx HMAC_DRBG context
- * \param additional Additional data to update state with, or NULL
- * \param add_len Length of additional data, or 0
- *
- * \note Additional data is optional, pass NULL and 0 as second
- * third argument if no additional data is being used.
+ * \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.
*/
MBEDTLS_DEPRECATED void mbedtls_hmac_drbg_update(
mbedtls_hmac_drbg_context *ctx,
@@ -293,26 +375,31 @@ MBEDTLS_DEPRECATED void mbedtls_hmac_drbg_update(
#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 */
@@ -320,9 +407,10 @@ 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
diff --git a/library/version_features.c b/library/version_features.c
index a99ee808d..3b67b2be8 100644
--- a/library/version_features.c
+++ b/library/version_features.c
@@ -297,6 +297,9 @@ static const char *features[] = {
#if defined(MBEDTLS_CIPHER_PADDING_ZEROS)
"MBEDTLS_CIPHER_PADDING_ZEROS",
#endif /* MBEDTLS_CIPHER_PADDING_ZEROS */
+#if defined(MBEDTLS_CTR_DRBG_USE_128_BIT_KEY)
+ "MBEDTLS_CTR_DRBG_USE_128_BIT_KEY",
+#endif /* MBEDTLS_CTR_DRBG_USE_128_BIT_KEY */
#if defined(MBEDTLS_ENABLE_WEAK_CIPHERSUITES)
"MBEDTLS_ENABLE_WEAK_CIPHERSUITES",
#endif /* MBEDTLS_ENABLE_WEAK_CIPHERSUITES */
diff --git a/programs/ssl/query_config.c b/programs/ssl/query_config.c
index bfb92720b..37e4141e9 100644
--- a/programs/ssl/query_config.c
+++ b/programs/ssl/query_config.c
@@ -834,6 +834,14 @@ int query_config( const char *config )
}
#endif /* MBEDTLS_CIPHER_PADDING_ZEROS */
+#if defined(MBEDTLS_CTR_DRBG_USE_128_BIT_KEY)
+ if( strcmp( "MBEDTLS_CTR_DRBG_USE_128_BIT_KEY", config ) == 0 )
+ {
+ MACRO_EXPANSION_TO_STR( MBEDTLS_CTR_DRBG_USE_128_BIT_KEY );
+ return( 0 );
+ }
+#endif /* MBEDTLS_CTR_DRBG_USE_128_BIT_KEY */
+
#if defined(MBEDTLS_ENABLE_WEAK_CIPHERSUITES)
if( strcmp( "MBEDTLS_ENABLE_WEAK_CIPHERSUITES", config ) == 0 )
{
@@ -2114,14 +2122,6 @@ int query_config( const char *config )
}
#endif /* MBEDTLS_CTR_DRBG_MAX_SEED_INPUT */
-#if defined(MBEDTLS_CTR_DRBG_USE_128_BIT_KEY)
- if( strcmp( "MBEDTLS_CTR_DRBG_USE_128_BIT_KEY", config ) == 0 )
- {
- MACRO_EXPANSION_TO_STR( MBEDTLS_CTR_DRBG_USE_128_BIT_KEY );
- return( 0 );
- }
-#endif /* MBEDTLS_CTR_DRBG_USE_128_BIT_KEY */
-
#if defined(MBEDTLS_HMAC_DRBG_RESEED_INTERVAL)
if( strcmp( "MBEDTLS_HMAC_DRBG_RESEED_INTERVAL", config ) == 0 )
{
diff --git a/scripts/config.pl b/scripts/config.pl
index 7afc89875..c2be0ba56 100755
--- a/scripts/config.pl
+++ b/scripts/config.pl
@@ -87,6 +87,7 @@ MBEDTLS_TEST_NULL_ENTROPY
MBEDTLS_DEPRECATED_REMOVED
MBEDTLS_HAVE_SSE2
MBEDTLS_PLATFORM_NO_STD_FUNCTIONS
+MBEDTLS_CTR_DRBG_USE_128_BIT_KEY
MBEDTLS_ECP_DP_M221_ENABLED
MBEDTLS_ECP_DP_M383_ENABLED
MBEDTLS_ECP_DP_M511_ENABLED