CTR_DRBG: support set_entropy_len() before seed()
mbedtls_ctr_drbg_seed() always set the entropy length to the default,
so a call to mbedtls_ctr_drbg_set_entropy_len() before seed() had no
effect. Change this to the more intuitive behavior that
set_entropy_len() sets the entropy length and seed() respects that and
only uses the default entropy length if there was no call to
set_entropy_len().
The former test-only function mbedtls_ctr_drbg_seed_entropy_len() is
no longer used, but keep it for strict ABI compatibility.
diff --git a/include/mbedtls/ctr_drbg.h b/include/mbedtls/ctr_drbg.h
index 766e647..c14507f 100644
--- a/include/mbedtls/ctr_drbg.h
+++ b/include/mbedtls/ctr_drbg.h
@@ -214,11 +214,8 @@
* with mbedtls_entropy_init() (which registers the platform's default
* entropy sources).
*
- * \p f_entropy is always called with a buffer size equal to the entropy
- * length. The entropy length is initially #MBEDTLS_CTR_DRBG_ENTROPY_LEN
- * and this value is always used for the initial seeding. You can change
- * the entropy length for subsequent seeding by calling
- * mbedtls_ctr_drbg_set_entropy_len() after this function.
+ * The entropy length is #MBEDTLS_CTR_DRBG_ENTROPY_LEN by default.
+ * You can override it by calling mbedtls_ctr_drbg_set_entropy_len().
*
* You can provide a personalization string in addition to the
* entropy source, to make this instantiation as unique as possible.
@@ -255,6 +252,8 @@
* \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 buffer size
+ * 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
@@ -298,15 +297,10 @@
/**
* \brief This function sets the amount of entropy grabbed on each
- * subsequent reseed.
+ * seed or reseed.
*
* The default value is #MBEDTLS_CTR_DRBG_ENTROPY_LEN.
*
- * \note mbedtls_ctr_drbg_seed() always sets the entropy length
- * to #MBEDTLS_CTR_DRBG_ENTROPY_LEN, so this function
- * only has an effect when it is called after
- * mbedtls_ctr_drbg_seed().
- *
* \note The security strength of CTR_DRBG is bounded by the
* entropy length. Thus:
* - When using AES-256