Improve CTR-DRBG documentation
- Rephrase file/function/parameter/enum/define/error descriptions into full
and clear sentences.
- Make sure to adhere to the Arm writing guidelines.
- Fix missing/incorrect Doxygen tags.
- Standardize terminology used within the file.
- Add full standard name in file description.
GitHub PR: #1316
diff --git a/include/mbedtls/ctr_drbg.h b/include/mbedtls/ctr_drbg.h
index 01cd826..121575a 100644
--- a/include/mbedtls/ctr_drbg.h
+++ b/include/mbedtls/ctr_drbg.h
@@ -1,10 +1,13 @@
/**
* \file ctr_drbg.h
*
- * \brief CTR_DRBG based on AES-256 (NIST SP 800-90)
+ * \brief CTR_DRBG is based on AES-256, as defined 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) 2006-2018, 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
@@ -19,8 +22,9 @@
* See the License for the specific language governing permissions and
* limitations under the License.
*
- * This file is part of mbed TLS (https://tls.mbed.org)
+ * This file is part of Mbed TLS (https://tls.mbed.org)
*/
+
#ifndef MBEDTLS_CTR_DRBG_H
#define MBEDTLS_CTR_DRBG_H
@@ -31,78 +35,95 @@
#endif
#define MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED -0x0034 /**< The entropy source failed. */
-#define MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG -0x0036 /**< Too many random requested in single call. */
-#define MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG -0x0038 /**< Input too large (Entropy + additional). */
-#define MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR -0x003A /**< Read/write error in file. */
+#define MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG -0x0036 /**< The requested random buffer length is too big. */
+#define MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG -0x0038 /**< The input (entropy + additional data) is too large. */
+#define MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR -0x003A /**< Read or write error in file. */
-#define MBEDTLS_CTR_DRBG_BLOCKSIZE 16 /**< Block size used by the cipher */
-#define MBEDTLS_CTR_DRBG_KEYSIZE 32 /**< Key size used by the cipher */
-#define MBEDTLS_CTR_DRBG_KEYBITS ( MBEDTLS_CTR_DRBG_KEYSIZE * 8 )
-#define MBEDTLS_CTR_DRBG_SEEDLEN ( MBEDTLS_CTR_DRBG_KEYSIZE + MBEDTLS_CTR_DRBG_BLOCKSIZE )
- /**< The seed length (counter + AES key) */
+#define MBEDTLS_CTR_DRBG_BLOCKSIZE 16 /**< The block size used by the cipher. */
+#define MBEDTLS_CTR_DRBG_KEYSIZE 32 /**< The key size used by the cipher. */
+#define MBEDTLS_CTR_DRBG_KEYBITS ( MBEDTLS_CTR_DRBG_KEYSIZE * 8 ) /**< The key size for the DRBG operation, in bits. */
+#define MBEDTLS_CTR_DRBG_SEEDLEN ( MBEDTLS_CTR_DRBG_KEYSIZE + MBEDTLS_CTR_DRBG_BLOCKSIZE ) /**< The seed length, calculated as (counter + AES key). */
/**
* \name SECTION: Module settings
*
* The configuration options you can set for this module are in this section.
- * Either change them in config.h or define them on the compiler command line.
+ * Either change them in config.h or define them using the compiler command
+ * line.
* \{
*/
#if !defined(MBEDTLS_CTR_DRBG_ENTROPY_LEN)
#if defined(MBEDTLS_SHA512_C) && !defined(MBEDTLS_ENTROPY_FORCE_SHA256)
-#define MBEDTLS_CTR_DRBG_ENTROPY_LEN 48 /**< Amount of entropy used per seed by default (48 with SHA-512, 32 with SHA-256) */
+#define MBEDTLS_CTR_DRBG_ENTROPY_LEN 48
+/**< The amount of entropy used per seed by default:
+ * <ul><li>48 with SHA-512.</li>
+ * <li>32 with SHA-256.</li></ul>
+ */
#else
-#define MBEDTLS_CTR_DRBG_ENTROPY_LEN 32 /**< Amount of entropy used per seed by default (48 with SHA-512, 32 with SHA-256) */
+#define MBEDTLS_CTR_DRBG_ENTROPY_LEN 32
+/**< Amount of entropy used per seed by default:
+ * <ul><li>48 with SHA-512.</li>
+ * <li>32 with SHA-256.</li></ul>
+ */
#endif
#endif
#if !defined(MBEDTLS_CTR_DRBG_RESEED_INTERVAL)
-#define MBEDTLS_CTR_DRBG_RESEED_INTERVAL 10000 /**< Interval before reseed is performed by default */
+#define MBEDTLS_CTR_DRBG_RESEED_INTERVAL 10000
+/**< The interval before reseed is performed by default. */
#endif
#if !defined(MBEDTLS_CTR_DRBG_MAX_INPUT)
-#define MBEDTLS_CTR_DRBG_MAX_INPUT 256 /**< Maximum number of additional input bytes */
+#define MBEDTLS_CTR_DRBG_MAX_INPUT 256
+/**< The maximum number of additional input Bytes. */
#endif
#if !defined(MBEDTLS_CTR_DRBG_MAX_REQUEST)
-#define MBEDTLS_CTR_DRBG_MAX_REQUEST 1024 /**< Maximum number of requested bytes per call */
+#define MBEDTLS_CTR_DRBG_MAX_REQUEST 1024
+/**< The maximum number of requested Bytes per call. */
#endif
#if !defined(MBEDTLS_CTR_DRBG_MAX_SEED_INPUT)
-#define MBEDTLS_CTR_DRBG_MAX_SEED_INPUT 384 /**< Maximum size of (re)seed buffer */
+#define MBEDTLS_CTR_DRBG_MAX_SEED_INPUT 384
+/**< The maximum size of seed or reseed buffer. */
#endif
/* \} name SECTION: Module settings */
-#define MBEDTLS_CTR_DRBG_PR_OFF 0 /**< No prediction resistance */
-#define MBEDTLS_CTR_DRBG_PR_ON 1 /**< Prediction resistance enabled */
+#define MBEDTLS_CTR_DRBG_PR_OFF 0
+/**< Prediction resistance is disabled. */
+#define MBEDTLS_CTR_DRBG_PR_ON 1
+/**< Prediction resistance is enabled. */
#ifdef __cplusplus
extern "C" {
#endif
/**
- * \brief CTR_DRBG context structure
+ * \brief The CTR_DRBG context structure.
*/
typedef struct
{
- unsigned char counter[16]; /*!< counter (V) */
- int reseed_counter; /*!< reseed counter */
- int prediction_resistance; /*!< enable prediction resistance (Automatic
- reseed before every random generation) */
- size_t entropy_len; /*!< amount of entropy grabbed on each
- (re)seed */
- int reseed_interval; /*!< reseed interval */
+ unsigned char counter[16]; /*!< The counter (V). */
+ int reseed_counter; /*!< The reseed counter. */
+ int prediction_resistance; /*!< This determines whether prediction
+ resistance is enabled, that is
+ whether to systematically reseed before
+ each random generation. */
+ size_t entropy_len; /*!< The amount of entropy grabbed on each
+ seed or reseed operation. */
+ int reseed_interval; /*!< The reseed interval. */
- mbedtls_aes_context aes_ctx; /*!< AES context */
+ mbedtls_aes_context aes_ctx; /*!< The AES context. */
/*
* Callbacks (Entropy)
*/
int (*f_entropy)(void *, unsigned char *, size_t);
+ /*!< The entropy callback function. */
- void *p_entropy; /*!< context for the entropy function */
+ void *p_entropy; /*!< The context for the entropy function. */
#if defined(MBEDTLS_THREADING_C)
mbedtls_threading_mutex_t mutex;
@@ -111,31 +132,32 @@
mbedtls_ctr_drbg_context;
/**
- * \brief CTR_DRBG context initialization
- * Makes the context ready for mbedtls_ctr_drbg_seed() or
- * mbedtls_ctr_drbg_free().
+ * \brief This function initializes the CTR_DRBG context,
+ * and prepares it for mbedtls_ctr_drbg_seed()
+ * or mbedtls_ctr_drbg_free().
*
- * \param ctx CTR_DRBG context to be initialized
+ * \param ctx The CTR_DRBG context to initialize.
*/
void mbedtls_ctr_drbg_init( mbedtls_ctr_drbg_context *ctx );
/**
- * \brief CTR_DRBG initial seeding
- * Seed and setup entropy source for future reseeds.
+ * \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.
+ * \note Personalization data can be provided in addition to the more generic
+ * entropy source, to make this instantiation as unique as possible.
*
- * \param ctx CTR_DRBG context to be seeded
- * \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
+ * \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.
*
- * \return 0 if successful, or
- * MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED
+ * \return \c 0 on success, or
+ * #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure.
*/
int mbedtls_ctr_drbg_seed( mbedtls_ctr_drbg_context *ctx,
int (*f_entropy)(void *, unsigned char *, size_t),
@@ -144,138 +166,147 @@
size_t len );
/**
- * \brief Clear CTR_CRBG context data
+ * \brief This function clears CTR_CRBG context data.
*
- * \param ctx CTR_DRBG context to clear
+ * \param ctx The CTR_DRBG context to clear.
*/
void mbedtls_ctr_drbg_free( mbedtls_ctr_drbg_context *ctx );
/**
- * \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_ctr_drbg_random_with_add().
+ * Only use this if your entropy source has sufficient
+ * throughput.
*
- * \param ctx CTR_DRBG context
- * \param resistance MBEDTLS_CTR_DRBG_PR_ON or MBEDTLS_CTR_DRBG_PR_OFF
+ * \param ctx The CTR_DRBG context.
+ * \param resistance #MBEDTLS_CTR_DRBG_PR_ON or #MBEDTLS_CTR_DRBG_PR_OFF.
*/
void mbedtls_ctr_drbg_set_prediction_resistance( mbedtls_ctr_drbg_context *ctx,
int resistance );
/**
- * \brief Set the amount of entropy grabbed on each (re)seed
- * (Default: MBEDTLS_CTR_DRBG_ENTROPY_LEN)
+ * \brief This function sets the amount of entropy grabbed on each
+ * seed or reseed. The default value is
+ * #MBEDTLS_CTR_DRBG_ENTROPY_LEN.
*
- * \param ctx CTR_DRBG context
- * \param len Amount of entropy to grab
+ * \param ctx The CTR_DRBG context.
+ * \param len The amount of entropy to grab.
*/
void mbedtls_ctr_drbg_set_entropy_len( mbedtls_ctr_drbg_context *ctx,
size_t len );
/**
- * \brief Set the reseed interval
- * (Default: MBEDTLS_CTR_DRBG_RESEED_INTERVAL)
+ * \brief This function sets the reseed interval.
+ * The default value is #MBEDTLS_CTR_DRBG_RESEED_INTERVAL.
*
- * \param ctx CTR_DRBG context
- * \param interval Reseed interval
+ * \param ctx The CTR_DRBG context.
+ * \param interval The reseed interval.
*/
void mbedtls_ctr_drbg_set_reseed_interval( mbedtls_ctr_drbg_context *ctx,
int interval );
/**
- * \brief CTR_DRBG reseeding (extracts data from entropy source)
+ * \brief This function reseeds the CTR_DRBG context, that is
+ * extracts data from the entropy source.
*
- * \param ctx CTR_DRBG context
- * \param additional Additional data to add to state (Can be NULL)
- * \param len Length of additional data
+ * \param ctx The CTR_DRBG context.
+ * \param additional Additional data to add to the state. Can be NULL.
+ * \param len The length of the additional data.
*
- * \return 0 if successful, or
- * MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED
+ * \return \c 0 on success, or
+ * #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure.
*/
int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
const unsigned char *additional, size_t len );
/**
- * \brief CTR_DRBG update state
+ * \brief This function updates the state of the CTR_DRBG context.
*
- * \param ctx CTR_DRBG context
- * \param additional Additional data to update state with
- * \param add_len Length of additional data
+ * \param ctx The CTR_DRBG context.
+ * \param additional The data to update the state with.
+ * \param add_len Length of \p additional data.
*
- * \note If add_len is greater than MBEDTLS_CTR_DRBG_MAX_SEED_INPUT,
- * only the first MBEDTLS_CTR_DRBG_MAX_SEED_INPUT bytes are used,
- * the remaining ones are silently discarded.
+ * \note If \p add_len is greater than #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT,
+ * only the first #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT Bytes are used.
+ * The remaining Bytes are silently discarded.
*/
void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
const unsigned char *additional, size_t add_len );
/**
- * \brief CTR_DRBG generate random with additional update input
+ * \brief This function updates a CTR_DRBG instance with additional
+ * data and uses it to generate random data.
*
- * Note: Automatically reseeds if reseed_counter is reached.
+ * \note The function automatically reseeds if the reseed counter is exceeded.
*
- * \param p_rng CTR_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
+ * \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.
*
- * \return 0 if successful, or
- * MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED, or
- * MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG
+ * \return \c 0 on success, or
+ * #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
+ * #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure.
*/
int mbedtls_ctr_drbg_random_with_add( void *p_rng,
unsigned char *output, size_t output_len,
const unsigned char *additional, size_t add_len );
/**
- * \brief CTR_DRBG generate random
+ * \brief This function uses CTR_DRBG to generate random data.
*
- * Note: Automatically reseeds if reseed_counter is reached.
+ * \note The function automatically reseeds if the reseed counter is exceeded.
*
- * \param p_rng CTR_DRBG context
- * \param output Buffer to fill
- * \param output_len Length of the buffer
+ * \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.
*
- * \return 0 if successful, or
- * MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED, or
- * MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG
+ * \return \c 0 on success, or
+ * #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
+ * #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure.
*/
int mbedtls_ctr_drbg_random( void *p_rng,
unsigned char *output, size_t output_len );
#if defined(MBEDTLS_FS_IO)
/**
- * \brief Write a seed file
+ * \brief This function writes a seed file.
*
- * \param ctx CTR_DRBG context
- * \param path Name of the file
+ * \param ctx The CTR_DRBG context.
+ * \param path The name of the file.
*
- * \return 0 if successful,
- * MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error, or
- * MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED
+ * \return \c 0 on success,
+ * #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error, or
+ * #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on
+ * failure.
*/
int mbedtls_ctr_drbg_write_seed_file( mbedtls_ctr_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 CTR_DRBG context
- * \param path Name of the file
+ * \param ctx The CTR_DRBG context.
+ * \param path The name of the file.
*
- * \return 0 if successful,
- * 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
+ * \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.
*/
int mbedtls_ctr_drbg_update_seed_file( mbedtls_ctr_drbg_context *ctx, const char *path );
#endif /* MBEDTLS_FS_IO */
/**
- * \brief Checkup routine
+ * \brief The CTR_DRBG checkup routine.
*
- * \return 0 if successful, or 1 if the test failed
+ * \return \c 0 on success, or \c 1 on failure.
*/
int mbedtls_ctr_drbg_self_test( int verbose );
diff --git a/library/error.c b/library/error.c
index eaf75ad..ac99091 100644
--- a/library/error.c
+++ b/library/error.c
@@ -658,11 +658,11 @@
if( use_ret == -(MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED) )
mbedtls_snprintf( buf, buflen, "CTR_DRBG - The entropy source failed" );
if( use_ret == -(MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG) )
- mbedtls_snprintf( buf, buflen, "CTR_DRBG - Too many random requested in single call" );
+ mbedtls_snprintf( buf, buflen, "CTR_DRBG - The requested random buffer length is too big" );
if( use_ret == -(MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG) )
- mbedtls_snprintf( buf, buflen, "CTR_DRBG - Input too large (Entropy + additional)" );
+ mbedtls_snprintf( buf, buflen, "CTR_DRBG - The input (entropy + additional data) is too large" );
if( use_ret == -(MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR) )
- mbedtls_snprintf( buf, buflen, "CTR_DRBG - Read/write error in file" );
+ mbedtls_snprintf( buf, buflen, "CTR_DRBG - Read or write error in file" );
#endif /* MBEDTLS_CTR_DRBG_C */
#if defined(MBEDTLS_DES_C)