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From deeb93c2fb7cc131741ced4877b75bcd3a64cef4 Mon Sep 17 00:00:00 2001
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From: Andreas Schneider <asn@samba.org>
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Date: Wed, 31 Jul 2019 15:38:50 +0200
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Subject: [PATCH 070/187] lib:util: Add better documentation for
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generate_secret_buffer()
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Signed-off-by: Andreas Schneider <asn@samba.org>
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Reviewed-by: Andrew Bartlett <abartlet@samba.org>
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(cherry picked from commit bf52ab7d2982de84a68a1b9c6d2f68250b7e7cca)
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---
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lib/util/genrand.c | 17 ++++++++++++-----
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lib/util/genrand.h | 6 +++++-
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2 files changed, 17 insertions(+), 6 deletions(-)
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diff --git a/lib/util/genrand.c b/lib/util/genrand.c
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index 76c2cb81962..a5809aa2bc9 100644
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--- a/lib/util/genrand.c
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+++ b/lib/util/genrand.c
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@@ -25,19 +25,26 @@
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#include <gnutls/gnutls.h>
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#include <gnutls/crypto.h>
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+/*
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+ * Details about the GnuTLS CSPRNG:
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+ *
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+ * https://nikmav.blogspot.com/2017/03/improving-by-simplifying-gnutls-prng.html
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+ */
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+
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_PUBLIC_ void generate_random_buffer(uint8_t *out, int len)
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{
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/* Thread and fork safe random number generator for temporary keys. */
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gnutls_rnd(GNUTLS_RND_RANDOM, out, len);
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}
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-/*
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- * Keep generate_secret_buffer in case we ever want to do something
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- * different
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- */
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_PUBLIC_ void generate_secret_buffer(uint8_t *out, int len)
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{
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- /* Thread and fork safe random number generator for long term keys. */
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+ /* The key generator, will re-seed after a fixed amount of bytes is
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+ * generated (typically less than the nonce), and will also re-seed
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+ * based on time, i.e., after few hours of operation without reaching
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+ * the limit for a re-seed. For its re-seed it mixes mixes data obtained
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+ * from the OS random device with the previous key.
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+ */
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gnutls_rnd(GNUTLS_RND_KEY, out, len);
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}
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diff --git a/lib/util/genrand.h b/lib/util/genrand.h
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index 5af23100596..abb8ce2c10a 100644
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--- a/lib/util/genrand.h
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+++ b/lib/util/genrand.h
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@@ -25,7 +25,11 @@
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void generate_random_buffer(uint8_t *out, int len);
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/**
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- * Thread and fork safe random number generator for long term keys.
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+ * @brief Generate random values for key buffers (e.g. session keys)
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+ *
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+ * @param[in] out A pointer to the buffer to fill with random data.
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+ *
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+ * @param[in] len The size of the buffer to fill.
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*/
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void generate_secret_buffer(uint8_t *out, int len);
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--
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2.23.0
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