Add remaining documentation

[libcontrac.git] / src / dtk.c

diff --git a/src/dtk.c b/src/dtk.c
index 3febd9f..5faffd7 100644 (file)
--- a/src/dtk.c
+++ b/src/dtk.c
@@ -1,17 +1,24 @@
-/** \ingroup contrac
+/** \ingroup DailyTracingKey
  * @file
- * @author     David Llewellyn-Jones
+ * @author     David Llewellyn-Jones <david@flypig.co.uk>
  * @version    $(VERSION)
  *
  * @section LICENSE
  *
+ * Copyright David Llewellyn-Jones, 2020
+ * Released under the GPLv2.
  *
- *
- * @brief
+ * @brief Daily Tracing Key functionality
  * @section DESCRIPTION
  *
+ * This class is used to generate and manage the Daily Tracing Key (DTK). It's
+ * largely internal. The functionality from \ref Contrac should generally be
+ * used in preference to this.
  *
- *
+ */
+
+/** \addtogroup DailyTracingKey
+ *  @{
  */
 
 // Includes
@@ -34,10 +41,25 @@
 
 // Defines
 
+/**
+ * Used internally.
+ *
+ * This is the prefix for the Info parameter provided to the HKDF and used to
+ * generate the DTK.
+ */
 #define DTK_INFO_PREFIX "CT-DTK"
 
 // Structures
 
+/**
+ * @brief The structure used to represent a Daily Tracing Key.
+ *
+ * This is an opaque structure that contains information about the DTK..
+ *
+ * This must be passed as the first parameter of every non-static function.
+ *
+ * The structure typedef is in dtk.h
+ */
 struct _Dtk {
        // Daily key
        unsigned char dtk[DTK_SIZE];
@@ -48,6 +70,11 @@ struct _Dtk {
 
 // Function definitions
 
+/**
+ * Creates a new instance of the class.
+ *
+ * @return The newly created object.
+ */
 Dtk * dtk_new() {
        Dtk * data;
        
@@ -56,6 +83,11 @@ Dtk * dtk_new() {
        return data;
 }
 
+/**
+ * Deletes an instance of the class, freeing up the memory allocated to it.
+ *
+ * @param data The instance to free.
+ */
 void dtk_delete(Dtk * data) {
        if (data) {
                // Clear the data for security
@@ -65,12 +97,25 @@ void dtk_delete(Dtk * data) {
        }
 }
 
-bool contrac_generate_daily_key(Dtk * data, Contrac const * contrac, uint32_t day_number) {
+/**
+ * Generates a Daily Tracing Key based on the day number provided.
+ *
+ * The operation may fail under certain circumstances, such as if the
+ * HKDF operation fails for some reason.
+ *
+ * For internal use. It generally makes more sense to use the
+ * contrac_set_day_number() function instead.
+ *
+ * @param data The context object to work with.
+ * @param day_number The day number to use to generate the key.
+ * @return true if the operation completed successfully, false otherwise.
+ */
+bool dtk_generate_daily_key(Dtk * data, Contrac const * contrac, uint32_t day_number) {
        int result = 1;
        char encode[sizeof(DTK_INFO_PREFIX) + sizeof(day_number)];
        size_t out_length = 0;
        EVP_PKEY_CTX *pctx = NULL;
-       const unsigned char * tk;
+       unsigned char const * tk;
 
        // dtk_i <- HKDF(tk, NULL, (UTF8("CT-DTK") || D_i), 16)
 
@@ -123,17 +168,62 @@ bool contrac_generate_daily_key(Dtk * data, Contrac const * contrac, uint32_t da
        return (result > 0);
 }
 
-const unsigned char * dtk_get_daily_key(Dtk const * data) {
+/**
+ * Gets the Daily Tracing Key for the device in binary format.
+ *
+ * For internal use. It generally makes more sense to use the
+ * contrac_get_daily_key() function instead.
+ *
+ * This allows the Daily Tracing Key to be extracted. The Daily Tracing Key
+ * should be kept secret (to maintain privacy) until a positive test is
+ * confirmed, at which point the user may choose to upload the key to a
+ * Diagnosis Server, so that others can be notified.
+ *
+ * The buffer returned will contain exactly DTK_SIZE (16) bytes of data in
+ * binary format. This may therefore contain null bytes, and the buffer will not
+ * necessarily be null terminated. Future operations may cause the data to
+ * change, so the caller should make a copy of the buffer rather than keeping
+ * a pointer to it.
+ *
+ * @param data The context object to work with.
+ * @return The Daily Tracing Key in binary format, not null terminated.
+ */
+unsigned char const * dtk_get_daily_key(Dtk const * data) {
        return data->dtk;
 }
 
+/**
+ * Gets the day number that applies to the current DTK.
+ *
+ * For internal use. It generally makes more sense to use the
+ * contrac_get_day_number() function instead.
+ *
+ * @param data The context object to work with.
+ * @return The day number stored in the object..
+ */
 uint32_t dtk_get_day_number(Dtk const * data) {
        return data->day_number;
 }
 
+/**
+ * Populates the data structure.
+ *
+ * Allows the DTK and day number values of the object to be set explicitly.
+ *
+ * For internal use. To set the DTK it generally makes more sense to use one of
+ * eiher contrac_set_day_number() or contrac_update_current_time() instead.
+ *
+ * The dtk_bytes buffer passed in must contain exactly DTK_SIZE (16) bytes of
+ * data. It doen't have to be null terminated.
+ *
+ * @param data The context object to work with.
+ * @param dtk_bytes The DTK value to set, in binary format.
+ * @param day_number The day number to associate with this DTK.
+ */
 void dtk_assign(Dtk * data, unsigned char const * dtk_bytes, uint32_t day_number) {
        memcpy(data->dtk, dtk_bytes, DTK_SIZE);
        data->day_number = day_number;
 }
 
+/** @} addtogroup DailyTracingKey */