diff --git a/include/mbedtls/hmac_drbg.h b/include/mbedtls/hmac_drbg.h index 8b4be8756..95aac3b23 100644 --- a/include/mbedtls/hmac_drbg.h +++ b/include/mbedtls/hmac_drbg.h @@ -139,13 +139,13 @@ void mbedtls_hmac_drbg_init( mbedtls_hmac_drbg_context *ctx ); * 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(). + * mbedtls_hmac_drbg_set_entropy_len() afterwards. * - * \note The default entropy length is the security strength - * (converted from bits to bytes). You can override - * it mbedtls_hmac_drbg_set_entropy_len(). - * \p f_entropy is always called with a length that is - * less than or equal to the entropy length. + * \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 @@ -156,6 +156,8 @@ void mbedtls_hmac_drbg_init( mbedtls_hmac_drbg_context *ctx ); * \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 @@ -222,13 +224,14 @@ void mbedtls_hmac_drbg_set_prediction_resistance( mbedtls_hmac_drbg_context *ctx /** * \brief This function sets the amount of entropy grabbed on each - * seed or reseed. + * reseed. * - * During the initial seeding, mbedtls_hmac_drbg_seed() additionally grabs - * half this amount to create the nonce. + * The default value is set by mbedtls_hmac_drbg_seed(). * - * The default value is given by the security strength, which depends on the - * hash used. See the documentation of mbedtls_hmac_drbg_seed() for details. + * \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.