From a2169368bbd92b77636e39b5cfe864a1236b083b Mon Sep 17 00:00:00 2001
From: Christian Grothoff <christian@grothoff.org>
Date: Thu, 28 Jan 2021 22:28:01 +0100
Subject: implement #6716

---
 src/include/gnunet_common.h     |  7 ++++++-
 src/include/gnunet_crypto_lib.h | 16 ++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

(limited to 'src/include')

diff --git a/src/include/gnunet_common.h b/src/include/gnunet_common.h
index 707108289..4dab71f7f 100644
--- a/src/include/gnunet_common.h
+++ b/src/include/gnunet_common.h
@@ -256,7 +256,12 @@ struct GNUNET_ShortHashCode
 
 
 /**
- * A UUID, a 128 bit random value.
+ * A UUID, a 128 bit "random" value.  We OFTEN use
+ * timeflakes (see: https://github.com/anthonynsimon/timeflake),
+ * where only 80 bits are random and the rest encodes
+ * a timestamp to improve database access.
+ *
+ * See #GNUNET_CRYPTO_random_timeflake().
  */
 struct GNUNET_Uuid
 {
diff --git a/src/include/gnunet_crypto_lib.h b/src/include/gnunet_crypto_lib.h
index 5521dad3c..d01457b4a 100644
--- a/src/include/gnunet_crypto_lib.h
+++ b/src/include/gnunet_crypto_lib.h
@@ -475,6 +475,22 @@ GNUNET_CRYPTO_random_block (enum GNUNET_CRYPTO_Quality mode,
                             void *buffer,
                             size_t length);
 
+
+/**
+ * @ingroup crypto
+ * Fill UUID with a timeflake pseudo-random value.  Note that
+ * timeflakes use only 80 bits of randomness and 48 bits
+ * to encode a timestamp in milliseconds. So what we return
+ * here is not a completely random number.
+ *
+ * @param mode desired quality of the random number
+ * @param uuid the value to fill
+ */
+void
+GNUNET_CRYPTO_random_timeflake (enum GNUNET_CRYPTO_Quality mode,
+                                struct GNUNET_Uuid *uuid);
+
+
 /**
  * @ingroup crypto
  * Produce a random value.
-- 
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