Improve message digest 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.
GitHub PR: #1319
diff --git a/include/mbedtls/md.h b/include/mbedtls/md.h
index 57c27a6..5e0376c 100644
--- a/include/mbedtls/md.h
+++ b/include/mbedtls/md.h
@@ -1,12 +1,12 @@
-/**
+ /**
* \file md.h
*
- * \brief Generic message digest wrapper
+ * \brief The generic message-digest wrapper.
*
* \author Adriaan de Jong <dejong@fox-it.com>
*/
/*
- * 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
@@ -21,8 +21,9 @@
* 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_MD_H
#define MBEDTLS_MD_H
@@ -64,65 +65,79 @@
#endif
/**
- * Opaque struct defined in md_internal.h
+ * Opaque struct defined in md_internal.h.
*/
typedef struct mbedtls_md_info_t mbedtls_md_info_t;
/**
- * Generic message digest context.
+ * The generic message-digest context.
*/
typedef struct {
- /** Information about the associated message digest */
+ /** Information about the associated message digest. */
const mbedtls_md_info_t *md_info;
- /** Digest-specific context */
+ /** The digest-specific context. */
void *md_ctx;
- /** HMAC part of the context */
+ /** The HMAC part of the context. */
void *hmac_ctx;
} mbedtls_md_context_t;
/**
- * \brief Returns the list of digests supported by the generic digest module.
+ * \brief This function returns the list of digests supported by the
+ * generic digest module.
*
- * \return a statically allocated array of digests, the last entry
- * is 0.
+ * \return A statically allocated array of digests. Each element
+ * in the returned list is an integer belonging to the
+ * message-digest enumeration #mbedtls_md_type_t.
+ * The last entry is 0.
*/
const int *mbedtls_md_list( void );
/**
- * \brief Returns the message digest information associated with the
- * given digest name.
+ * \brief This function returns the message-digest information
+ * associated with the given digest name.
*
- * \param md_name Name of the digest to search for.
+ * \param md_name The name of the digest to search for.
*
- * \return The message digest information associated with md_name or
- * NULL if not found.
+ * \return The message-digest information associated with \p md_name,
+ * or NULL if not found.
*/
const mbedtls_md_info_t *mbedtls_md_info_from_string( const char *md_name );
/**
- * \brief Returns the message digest information associated with the
- * given digest type.
+ * \brief This function returns the message-digest information
+ * associated with the given digest type.
*
- * \param md_type type of digest to search for.
+ * \param md_type The type of digest to search for.
*
- * \return The message digest information associated with md_type or
- * NULL if not found.
+ * \return The message-digest information associated with \p md_type,
+ * or NULL if not found.
*/
const mbedtls_md_info_t *mbedtls_md_info_from_type( mbedtls_md_type_t md_type );
/**
- * \brief Initialize a md_context (as NONE)
- * This should always be called first.
- * Prepares the context for mbedtls_md_setup() or mbedtls_md_free().
+ * \brief This function initializes a message-digest context without
+ * binding it to a particular message-digest algorithm.
+ *
+ * This function should always be called first. It prepares the
+ * context for mbedtls_md_setup() for binding it to a
+ * message-digest algorithm.
*/
void mbedtls_md_init( mbedtls_md_context_t *ctx );
/**
- * \brief Free and clear the internal structures of ctx.
- * Can be called at any time after mbedtls_md_init().
- * Mandatory once mbedtls_md_setup() has been called.
+ * \brief This function clears the internal structure of \p ctx and
+ * frees any embedded internal structure, but does not free
+ * \p ctx itself.
+ *
+ * If you have called mbedtls_md_setup() on \p ctx, you must
+ * call mbedtls_md_free() when you are no longer using the
+ * context.
+ * Calling this function if you have previously
+ * called mbedtls_md_init() and nothing else is optional.
+ * You must not call this function if you have not called
+ * mbedtls_md_init().
*/
void mbedtls_md_free( mbedtls_md_context_t *ctx );
@@ -133,220 +148,288 @@
#define MBEDTLS_DEPRECATED
#endif
/**
- * \brief Select MD to use and allocate internal structures.
- * Should be called after mbedtls_md_init() or mbedtls_md_free().
+ * \brief This function selects the message digest algorithm to use,
+ * and allocates internal structures.
+ *
+ * It should be called after mbedtls_md_init() or mbedtls_md_free().
* Makes it necessary to call mbedtls_md_free() later.
*
* \deprecated Superseded by mbedtls_md_setup() in 2.0.0
*
- * \param ctx Context to set up.
- * \param md_info Message digest to use.
+ * \param ctx The context to set up.
+ * \param md_info The information structure of the message-digest algorithm
+ * to use.
*
* \returns \c 0 on success,
- * \c MBEDTLS_ERR_MD_BAD_INPUT_DATA on parameter failure,
- * \c MBEDTLS_ERR_MD_ALLOC_FAILED memory allocation failure.
+ * #MBEDTLS_ERR_MD_BAD_INPUT_DATA on parameter failure,
+ * #MBEDTLS_ERR_MD_ALLOC_FAILED memory allocation failure.
*/
int mbedtls_md_init_ctx( mbedtls_md_context_t *ctx, const mbedtls_md_info_t *md_info ) MBEDTLS_DEPRECATED;
#undef MBEDTLS_DEPRECATED
#endif /* MBEDTLS_DEPRECATED_REMOVED */
/**
- * \brief Select MD to use and allocate internal structures.
- * Should be called after mbedtls_md_init() or mbedtls_md_free().
- * Makes it necessary to call mbedtls_md_free() later.
+ * \brief This function selects the message digest algorithm to use,
+ * and allocates internal structures.
*
- * \param ctx Context to set up.
- * \param md_info Message digest to use.
- * \param hmac 0 to save some memory if HMAC will not be used,
- * non-zero is HMAC is going to be used with this context.
+ * It should be called after mbedtls_md_init() or
+ * mbedtls_md_free(). Makes it necessary to call
+ * mbedtls_md_free() later.
+ *
+ * \param ctx The context to set up.
+ * \param md_info The information structure of the message-digest algorithm
+ * to use.
+ * \param hmac <ul><li>0: HMAC is not used. Saves some memory.</li>
+ * <li>non-zero: HMAC is used with this context.</li></ul>
*
* \returns \c 0 on success,
- * \c MBEDTLS_ERR_MD_BAD_INPUT_DATA on parameter failure,
- * \c MBEDTLS_ERR_MD_ALLOC_FAILED memory allocation failure.
+ * #MBEDTLS_ERR_MD_BAD_INPUT_DATA on parameter failure, or
+ * #MBEDTLS_ERR_MD_ALLOC_FAILED on memory allocation failure.
*/
int mbedtls_md_setup( mbedtls_md_context_t *ctx, const mbedtls_md_info_t *md_info, int hmac );
/**
- * \brief Clone the state of an MD context
+ * \brief This function clones the state of an message-digest
+ * context.
*
- * \note The two contexts must have been setup to the same type
- * (cloning from SHA-256 to SHA-512 make no sense).
+ * \note You must call mbedtls_md_setup() on \c dst before calling
+ * this function.
*
- * \warning Only clones the MD state, not the HMAC state! (for now)
+ * \note The two contexts must have the same type,
+ * for example, both are SHA-256.
*
- * \param dst The destination context
- * \param src The context to be cloned
+ * \warning This function clones the message-digest state, not the
+ * HMAC state.
+ *
+ * \param dst The destination context.
+ * \param src The context to be cloned.
*
* \return \c 0 on success,
- * \c MBEDTLS_ERR_MD_BAD_INPUT_DATA on parameter failure.
+ * #MBEDTLS_ERR_MD_BAD_INPUT_DATA on parameter failure.
*/
int mbedtls_md_clone( mbedtls_md_context_t *dst,
const mbedtls_md_context_t *src );
/**
- * \brief Returns the size of the message digest output.
+ * \brief This function extracts the message-digest size from the
+ * message-digest information structure.
*
- * \param md_info message digest info
+ * \param md_info The information structure of the message-digest algorithm
+ * to use.
*
- * \return size of the message digest output in bytes.
+ * \return The size of the message-digest output in Bytes.
*/
unsigned char mbedtls_md_get_size( const mbedtls_md_info_t *md_info );
/**
- * \brief Returns the type of the message digest output.
+ * \brief This function extracts the message-digest type from the
+ * message-digest information structure.
*
- * \param md_info message digest info
+ * \param md_info The information structure of the message-digest algorithm
+ * to use.
*
- * \return type of the message digest output.
+ * \return The type of the message digest.
*/
mbedtls_md_type_t mbedtls_md_get_type( const mbedtls_md_info_t *md_info );
/**
- * \brief Returns the name of the message digest output.
+ * \brief This function extracts the message-digest name from the
+ * message-digest information structure.
*
- * \param md_info message digest info
+ * \param md_info The information structure of the message-digest algorithm
+ * to use.
*
- * \return name of the message digest output.
+ * \return The name of the message digest.
*/
const char *mbedtls_md_get_name( const mbedtls_md_info_t *md_info );
/**
- * \brief Prepare the context to digest a new message.
- * Generally called after mbedtls_md_setup() or mbedtls_md_finish().
- * Followed by mbedtls_md_update().
+ * \brief This function starts a message-digest computation.
*
- * \param ctx generic message digest context.
+ * You must call this function after setting up the context
+ * with mbedtls_md_setup(), and before passing data with
+ * mbedtls_md_update().
*
- * \returns 0 on success, MBEDTLS_ERR_MD_BAD_INPUT_DATA if parameter
- * verification fails.
+ * \param ctx The generic message-digest context.
+ *
+ * \returns \c 0 on success, #MBEDTLS_ERR_MD_BAD_INPUT_DATA if
+ * parameter verification fails.
*/
int mbedtls_md_starts( mbedtls_md_context_t *ctx );
/**
- * \brief Generic message digest process buffer
- * Called between mbedtls_md_starts() and mbedtls_md_finish().
- * May be called repeatedly.
+ * \brief This function feeds an input buffer into an ongoing
+ * message-digest computation.
*
- * \param ctx Generic message digest context
- * \param input buffer holding the datal
- * \param ilen length of the input data
+ * You must call mbedtls_md_starts() before calling this
+ * function. You may call this function multiple times.
+ * Afterwards, call mbedtls_md_finish().
*
- * \returns 0 on success, MBEDTLS_ERR_MD_BAD_INPUT_DATA if parameter
- * verification fails.
+ * \param ctx The generic message-digest context.
+ * \param input The buffer holding the input data.
+ * \param ilen The length of the input data.
+ *
+ * \returns \c 0 on success, #MBEDTLS_ERR_MD_BAD_INPUT_DATA if
+ * parameter verification fails.
*/
int mbedtls_md_update( mbedtls_md_context_t *ctx, const unsigned char *input, size_t ilen );
/**
- * \brief Generic message digest final digest
- * Called after mbedtls_md_update().
- * Usually followed by mbedtls_md_free() or mbedtls_md_starts().
+ * \brief This function finishes the digest operation,
+ * and writes the result to the output buffer.
*
- * \param ctx Generic message digest context
- * \param output Generic message digest checksum result
+ * Call this function after a call to mbedtls_md_starts(),
+ * followed by any number of calls to mbedtls_md_update().
+ * Afterwards, you may either clear the context with
+ * mbedtls_md_free(), or call mbedtls_md_starts() to reuse
+ * the context for another digest operation with the same
+ * algorithm.
*
- * \returns 0 on success, MBEDTLS_ERR_MD_BAD_INPUT_DATA if parameter
- * verification fails.
+ * \param ctx The generic message-digest context.
+ * \param output The buffer for the generic message-digest checksum result.
+ *
+ * \returns \c 0 on success, or #MBEDTLS_ERR_MD_BAD_INPUT_DATA if
+ * parameter verification fails.
*/
int mbedtls_md_finish( mbedtls_md_context_t *ctx, unsigned char *output );
/**
- * \brief Output = message_digest( input buffer )
+ * \brief This function calculates the message-digest of a buffer,
+ * with respect to a configurable message-digest algorithm
+ * in a single call.
*
- * \param md_info message digest info
- * \param input buffer holding the data
- * \param ilen length of the input data
- * \param output Generic message digest checksum result
+ * The result is calculated as
+ * Output = message_digest(input buffer).
*
- * \returns 0 on success, MBEDTLS_ERR_MD_BAD_INPUT_DATA if parameter
- * verification fails.
+ * \param md_info The information structure of the message-digest algorithm
+ * to use.
+ * \param input The buffer holding the data.
+ * \param ilen The length of the input data.
+ * \param output The generic message-digest checksum result.
+ *
+ * \returns \c 0 on success, or #MBEDTLS_ERR_MD_BAD_INPUT_DATA if
+ * parameter verification fails.
*/
int mbedtls_md( const mbedtls_md_info_t *md_info, const unsigned char *input, size_t ilen,
unsigned char *output );
#if defined(MBEDTLS_FS_IO)
/**
- * \brief Output = message_digest( file contents )
+ * \brief This function calculates the message-digest checksum
+ * result of the contents of the provided file.
*
- * \param md_info message digest info
- * \param path input file name
- * \param output generic message digest checksum result
+ * The result is calculated as
+ * Output = message_digest(file contents).
*
- * \return 0 if successful,
- * MBEDTLS_ERR_MD_FILE_IO_ERROR if file input failed,
- * MBEDTLS_ERR_MD_BAD_INPUT_DATA if md_info was NULL.
+ * \param md_info The information structure of the message-digest algorithm
+ * to use.
+ * \param path The input file name.
+ * \param output The generic message-digest checksum result.
+ *
+ * \return \c 0 on success,
+ * #MBEDTLS_ERR_MD_FILE_IO_ERROR if file input failed, or
+ * #MBEDTLS_ERR_MD_BAD_INPUT_DATA if \p md_info was NULL.
*/
int mbedtls_md_file( const mbedtls_md_info_t *md_info, const char *path,
unsigned char *output );
#endif /* MBEDTLS_FS_IO */
/**
- * \brief Set HMAC key and prepare to authenticate a new message.
- * Usually called after mbedtls_md_setup() or mbedtls_md_hmac_finish().
+ * \brief This function sets the HMAC key and prepares to
+ * authenticate a new message.
*
- * \param ctx HMAC context
- * \param key HMAC secret key
- * \param keylen length of the HMAC key in bytes
+ * Call this function after mbedtls_md_setup(), to use
+ * the MD context for an HMAC calculation, then call
+ * mbedtls_md_hmac_update() to provide the input data, and
+ * mbedtls_md_hmac_finish() to get the HMAC value.
*
- * \returns 0 on success, MBEDTLS_ERR_MD_BAD_INPUT_DATA if parameter
- * verification fails.
+ * \param ctx The message digest context containing an embedded HMAC
+ * context.
+ * \param key The HMAC secret key.
+ * \param keylen The length of the HMAC key in Bytes.
+ *
+ * \returns \c 0 on success, or #MBEDTLS_ERR_MD_BAD_INPUT_DATA if
+ * parameter verification fails.
*/
int mbedtls_md_hmac_starts( mbedtls_md_context_t *ctx, const unsigned char *key,
size_t keylen );
/**
- * \brief Generic HMAC process buffer.
- * Called between mbedtls_md_hmac_starts() or mbedtls_md_hmac_reset()
- * and mbedtls_md_hmac_finish().
- * May be called repeatedly.
+ * \brief This function feeds an input buffer into an ongoing HMAC
+ * computation.
*
- * \param ctx HMAC context
- * \param input buffer holding the data
- * \param ilen length of the input data
+ * Call mbedtls_md_hmac_starts() or mbedtls_md_hmac_reset()
+ * before calling this function.
+ * You may call this function multiple times to pass the
+ * input piecewise.
+ * Afterwards, call mbedtls_md_hmac_finish().
*
- * \returns 0 on success, MBEDTLS_ERR_MD_BAD_INPUT_DATA if parameter
- * verification fails.
+ * \param ctx The message digest context containing an embedded HMAC
+ * context.
+ * \param input The buffer holding the input data.
+ * \param ilen The length of the input data.
+ *
+ * \returns \c 0 on success, or #MBEDTLS_ERR_MD_BAD_INPUT_DATA if
+ * parameter verification fails.
*/
int mbedtls_md_hmac_update( mbedtls_md_context_t *ctx, const unsigned char *input,
size_t ilen );
/**
- * \brief Output HMAC.
- * Called after mbedtls_md_hmac_update().
- * Usually followed by mbedtls_md_hmac_reset(),
- * mbedtls_md_hmac_starts(), or mbedtls_md_free().
+ * \brief This function finishes the HMAC operation, and writes
+ * the result to the output buffer.
*
- * \param ctx HMAC context
- * \param output Generic HMAC checksum result
+ * Call this function after mbedtls_md_hmac_starts() and
+ * mbedtls_md_hmac_update() to get the HMAC value. Afterwards
+ * you may either call mbedtls_md_free() to clear the context,
+ * or call mbedtls_md_hmac_reset() to reuse the context with
+ * the same HMAC key.
*
- * \returns 0 on success, MBEDTLS_ERR_MD_BAD_INPUT_DATA if parameter
- * verification fails.
+ * \param ctx The message digest context containing an embedded HMAC
+ * context.
+ * \param output The generic HMAC checksum result.
+ *
+ * \returns \c 0 on success, or #MBEDTLS_ERR_MD_BAD_INPUT_DATA if
+ * parameter verification fails.
*/
int mbedtls_md_hmac_finish( mbedtls_md_context_t *ctx, unsigned char *output);
/**
- * \brief Prepare to authenticate a new message with the same key.
- * Called after mbedtls_md_hmac_finish() and before
- * mbedtls_md_hmac_update().
+ * \brief This function prepares to authenticate a new message with
+ * the same key as the previous HMAC operation.
*
- * \param ctx HMAC context to be reset
+ * You may call this function after mbedtls_md_hmac_finish().
+ * Afterwards call mbedtls_md_hmac_update() to pass the new
+ * input.
*
- * \returns 0 on success, MBEDTLS_ERR_MD_BAD_INPUT_DATA if parameter
- * verification fails.
+ * \param ctx The message digest context containing an embedded HMAC
+ * context.
+ *
+ * \returns \c 0 on success, or #MBEDTLS_ERR_MD_BAD_INPUT_DATA if
+ * parameter verification fails.
*/
int mbedtls_md_hmac_reset( mbedtls_md_context_t *ctx );
/**
- * \brief Output = Generic_HMAC( hmac key, input buffer )
+ * \brief This function calculates the full generic HMAC
+ * on the input buffer with the provided key.
*
- * \param md_info message digest info
- * \param key HMAC secret key
- * \param keylen length of the HMAC key in bytes
- * \param input buffer holding the data
- * \param ilen length of the input data
- * \param output Generic HMAC-result
+ * The function allocates the context, performs the
+ * calculation, and frees the context.
*
- * \returns 0 on success, MBEDTLS_ERR_MD_BAD_INPUT_DATA if parameter
- * verification fails.
+ * The HMAC result is calculated as
+ * output = generic HMAC(hmac key, input buffer).
+ *
+ * \param md_info The information structure of the message-digest algorithm
+ * to use.
+ * \param key The HMAC secret key.
+ * \param keylen The length of the HMAC secret key in Bytes.
+ * \param input The buffer holding the input data.
+ * \param ilen The length of the input data.
+ * \param output The generic HMAC result.
+ *
+ * \returns \c 0 on success, or #MBEDTLS_ERR_MD_BAD_INPUT_DATA if
+ * parameter verification fails.
*/
int mbedtls_md_hmac( const mbedtls_md_info_t *md_info, const unsigned char *key, size_t keylen,
const unsigned char *input, size_t ilen,