CTR_DRBG: make it easier to understand the security strength

Explain how MBEDTLS_CTR_DRBG_ENTROPY_LEN is set next to the security
strength statement, rather than giving a partial explanation (current
setting only) in the documentation of MBEDTLS_CTR_DRBG_ENTROPY_LEN.
This commit is contained in:
Gilles Peskine 2019-10-02 18:23:38 +02:00
parent 340d6099a0
commit 8cec70a8c4

View File

@ -24,6 +24,13 @@
* and #MBEDTLS_CTR_DRBG_ENTROPY_LEN is set to 24 or more (which is
* always the case unless it is explicitly set to a different value
* in `config.h`).
*
* Note that the value of #MBEDTLS_CTR_DRBG_ENTROPY_LEN defaults to:
* - \c 48 if the module #MBEDTLS_SHA512_C is enabled and the symbol
* #MBEDTLS_ENTROPY_FORCE_SHA256 is not enabled at compile time.
* This is the default configuration of the library.
* - \c 32 if the module #MBEDTLS_SHA512_C is disabled at compile time.
* - \c 32 if #MBEDTLS_ENTROPY_FORCE_SHA256 is enabled at compile time.
*/
/*
* Copyright (C) 2006-2019, Arm Limited (or its affiliates), All Rights Reserved
@ -99,7 +106,7 @@
/** The amount of entropy used per seed by default.
*
* This is 48 bytes because the entropy module uses SHA-512
* (`MBEDTLS_ENTROPY_FORCE_SHA256` is not set).
* #MBEDTLS_ENTROPY_FORCE_SHA256 is not set).
*
* \note See mbedtls_ctr_drbg_set_entropy_len() regarding what values are
* acceptable.
@ -109,7 +116,7 @@
/** The amount of entropy used per seed by default.
*
* This is 32 bytes because the entropy module uses SHA-256
* (the SHA-512 module is disabled or `MBEDTLS_ENTROPY_FORCE_SHA256` is set).
* (the SHA512 module is disabled or #MBEDTLS_ENTROPY_FORCE_SHA256 is set).
*
* \note See mbedtls_ctr_drbg_set_entropy_len() regarding what values are
* acceptable.