diff --git a/include/mbedtls/ccm.h b/include/mbedtls/ccm.h
index 6210c1f..b2c57a4 100644
--- a/include/mbedtls/ccm.h
+++ b/include/mbedtls/ccm.h
@@ -92,7 +92,8 @@
  * \brief           This function initializes the CCM context set in the
  *                  \p ctx parameter and sets the encryption key.
  *
- * \param ctx       The CCM context to initialize. Must not be \c NULL.
+ * \param ctx       The CCM context to initialize. Must be an initialized
+ *                  context.
  * \param cipher    The 128-bit block cipher to use.
  * \param key       The encryption key. Must not be \c NULL.
  * \param keybits   The key size in bits. This must be acceptable by the cipher.
@@ -109,7 +110,7 @@
  * \brief   This function releases and clears the specified CCM context
  *          and underlying cipher sub-context.
  *
- * \param ctx       The CCM context to clear.
+ * \param ctx       The CCM context to clear. Must be an initialized context.
  *
  * \note            If ctx is \c NULL, the function has no effect.
  */
@@ -124,20 +125,27 @@
  *                  \p tag = \p output + \p length, and make sure that the
  *                  output buffer is at least \p length + \p tag_len wide.
  *
- * \param ctx       The CCM context to use for encryption. Must not be \c NULL.
+ * \param ctx       The CCM context to use for encryption. Must be an
+ *                  initialized context.
  * \param length    The length of the input data in Bytes.
- * \param iv        Initialization vector (nonce). Must not be \c NULL.
+ * \param iv        Initialization vector (nonce). Must be a readable buffer of
+ *                  at least \p iv_len Bytes.
  * \param iv_len    The length of the nonce in Bytes: 7, 8, 9, 10, 11, 12,
  *                  or 13. The length L of the message length field is
  *                  15 - \p iv_len.
- * \param add       The additional data field. Must not be \c NULL.
+ * \param add       The additional data field. If \p add_len is greater than
+ *                  zero, \p add must be a readable buffer of at least that
+ *                  length.
  * \param add_len   The length of additional data in Bytes.
  *                  Must be less than 2^16 - 2^8.
- * \param input     The buffer holding the input data. Must not be \c NULL.
- * \param output    The buffer holding the output data.
- *                  Must be at least \p length Bytes wide.
- * \param tag       The buffer holding the authentication field. Must not be
- *                  \c NULL.
+ * \param input     The buffer holding the input data. If \p length is greater
+ *                  than zero, \p input must be a readable buffer of at least
+ *                  that length.
+ * \param output    The buffer holding the output data. If \p length is greater
+ *                  than zero, \p output must be a writable buffer of at least
+ *                  that length.
+ * \param tag       The buffer holding the authentication field. Must be a
+ *                  readable buffer of at least \p tag_len Bytes.
  * \param tag_len   The length of the authentication field to generate in Bytes:
  *                  4, 6, 8, 10, 12, 14 or 16.
  *
@@ -163,20 +171,27 @@
  *                  the tag length has to be encoded into the \p iv passed to
  *                  this function.
  *
- * \param ctx       The CCM context to use for encryption. Must not be \c NULL.
+ * \param ctx       The CCM context to use for encryption. Must be an
+ *                  initialized context.
  * \param length    The length of the input data in Bytes.
- * \param iv        Initialization vector (nonce). Must not be \c NULL.
+ * \param iv        Initialization vector (nonce). Must be a readable buffer of
+ *                  at least \p iv_len Bytes.
  * \param iv_len    The length of the nonce in Bytes: 7, 8, 9, 10, 11, 12,
  *                  or 13. The length L of the message length field is
  *                  15 - \p iv_len.
- * \param add       The additional data field. Must not be \c NULL.
+ * \param add       The additional data field. If \p add_len is greater than
+ *                  zero, \p add must be a readable buffer of at least that
+ *                  length.
  * \param add_len   The length of additional data in Bytes.
  *                  Must be less than 2^16 - 2^8.
- * \param input     The buffer holding the input data. Must not be \c NULL.
- * \param output    The buffer holding the output data.
- *                  Must be at least \p length Bytes wide.
- * \param tag       The buffer holding the authentication field. Must not be
- *                  NULL.
+ * \param input     The buffer holding the input data. If \p length is greater
+ *                  than zero, \p input must be a readable buffer of at least
+ *                  that length.
+ * \param output    The buffer holding the output data. If \p length is greater
+ *                  than zero, \p output must be a writable buffer of at least
+ *                  that length.
+ * \param tag       The buffer holding the authentication field. Must be a
+ *                  readable buffer of at least \p tag_len Bytes.
  * \param tag_len   The length of the authentication field to generate in Bytes:
  *                  0, 4, 6, 8, 10, 12, 14 or 16.
  *
@@ -196,21 +211,28 @@
  * \brief           This function performs a CCM authenticated decryption of a
  *                  buffer.
  *
- * \param ctx       The CCM context to use for decryption. Must not be \c NULL.
+ * \param ctx       The CCM context to use for decryption. Must be an
+ *                  initialized context.
  * \param length    The length of the input data in Bytes.
- * \param iv        Initialization vector (nonce). Must not be \c NULL.
+ * \param iv        Initialization vector (nonce). Must be a readable buffer of
+ *                  at least \p iv_len Bytes.
  * \param iv_len    The length of the nonce in Bytes: 7, 8, 9, 10, 11, 12,
  *                  or 13. The length L of the message length field is
  *                  15 - \p iv_len.
- * \param add       The additional data field. Must not be \c NULL.
+ * \param add       The additional data field. If \p add_len is greater than
+ *                  zero, \p add must be a readable buffer of at least that
+ *                  length.
  * \param add_len   The length of additional data in Bytes.
  *                  Must be less than 2^16 - 2^8.
- * \param input     The buffer holding the input data. Must not be \c NULL.
- * \param output    The buffer holding the output data.
- *                  Must be at least \p length Bytes wide.
- * \param tag       The buffer holding the authentication field. Must not be
- *                  NULL.
- * \param tag_len   The length of the authentication field in Bytes.
+ * \param input     The buffer holding the input data. If \p length is greater
+ *                  than zero, \p input must be a readable buffer of at least
+ *                  that length.
+ * \param output    The buffer holding the output data. If \p length is greater
+ *                  than zero, \p output must be a writable buffer of at least
+ *                  that length.
+ * \param tag       The buffer holding the authentication field. Must be a
+ *                  readable buffer of at least \p tag_len Bytes.
+ * \param tag_len   The length of the authentication field to generate in Bytes:
  *                  4, 6, 8, 10, 12, 14 or 16.
  *
  * \return          \c 0 on success. This indicates that the message is authentic.
@@ -232,20 +254,27 @@
  *                  this function as \p tag_len. (\p tag needs to be adjusted
  *                  accordingly.)
  *
- * \param ctx       The CCM context to use for decryption. Must not be \c NULL.
+ * \param ctx       The CCM context to use for decryption. Must be an
+ *                  initialized context.
  * \param length    The length of the input data in Bytes.
- * \param iv        Initialization vector (nonce). Must not be \c NULL.
+ * \param iv        Initialization vector (nonce). Must be a readable buffer of
+ *                  at least \p iv_len Bytes.
  * \param iv_len    The length of the nonce in Bytes: 7, 8, 9, 10, 11, 12,
  *                  or 13. The length L of the message length field is
  *                  15 - \p iv_len.
- * \param add       The additional data field. Must not be \c NULL.
+ * \param add       The additional data field. If \p add_len is greater than
+ *                  zero, \p add must be a readable buffer of at least that
+ *                  length.
  * \param add_len   The length of additional data in Bytes.
  *                  Must be less than 2^16 - 2^8.
- * \param input     The buffer holding the input data. Must not be \c NULL.
- * \param output    The buffer holding the output data.
- *                  Must be at least \p length Bytes wide.
- * \param tag       The buffer holding the authentication field. Must not be
- *                  NULL.
+ * \param input     The buffer holding the input data. If \p length is greater
+ *                  than zero, \p input must be a readable buffer of at least
+ *                  that length.
+ * \param output    The buffer holding the output data. If \p length is greater
+ *                  than zero, \p output must be a writable buffer of at least
+ *                  that length.
+ * \param tag       The buffer holding the authentication field. Must be a
+ *                  readable buffer of at least \p tag_len Bytes.
  * \param tag_len   The length of the authentication field in Bytes.
  *                  0, 4, 6, 8, 10, 12, 14 or 16.
  *