lib:util: Add better documentation for generate_secret_buffer()

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

1 files changed, 12 insertions, 5 deletions

diff --git a/lib/util/genrand.c b/lib/util/genrand.c
index 76c2cb81962..a5809aa2bc9 100644
--- a/lib/util/genrand.c
+++ b/lib/util/genrand.c
@@ -25,19 +25,26 @@
 #include <gnutls/gnutls.h>
 #include <gnutls/crypto.h>
 
+/*
+ * Details about the GnuTLS CSPRNG:
+ *
+ * https://nikmav.blogspot.com/2017/03/improving-by-simplifying-gnutls-prng.html
+ */
+
 _PUBLIC_ void generate_random_buffer(uint8_t *out, int len)
 {
 	/* Thread and fork safe random number generator for temporary keys. */
 	gnutls_rnd(GNUTLS_RND_RANDOM, out, len);
 }
 
-/*
- * Keep generate_secret_buffer in case we ever want to do something
- * different
- */
 _PUBLIC_ void generate_secret_buffer(uint8_t *out, int len)
 {
-	/* Thread and fork safe random number generator for long term keys. */
+	/* The key generator, will re-seed after a fixed amount of bytes is
+	 * generated (typically less than the nonce), and will also re-seed
+	 * based on time, i.e., after few hours of operation without reaching
+	 * the limit for a re-seed. For its re-seed it mixes mixes data obtained
+	 * from the OS random device with the previous key.
+	 */
 	gnutls_rnd(GNUTLS_RND_KEY, out, len);
 }