From 9a9a466e83ca4cb8237199ec102c9af9a482647f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Niels=20M=C3=B6ller?= <nisse@lysator.liu.se>
Date: Mon, 5 Sep 2016 15:17:19 +0200
Subject: [PATCH] Define NETTLE_CURVE25519_RFC7748, and document it.
---
ChangeLog | 6 ++++++
curve25519.h | 3 +++
nettle.texinfo | 14 ++++++++++++++
3 files changed, 23 insertions(+)
diff --git a/ChangeLog b/ChangeLog
index 6d54149a..5e130699 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2016-09-05 Niels Möller <nisse@lysator.liu.se>
+
+ * curve25519.h (NETTLE_CURVE25519_RFC7748): New preprocessor
+ constant.
+ * nettle.texinfo: Document it.
+
2016-09-03 Niels Möller <nisse@lysator.liu.se>
* config.make.in (.SUFFIXES): Delete no longer used .p$(OBJEXT).
diff --git a/curve25519.h b/curve25519.h
index b47200b9..1dcd94da 100644
--- a/curve25519.h
+++ b/curve25519.h
@@ -44,6 +44,9 @@ extern "C" {
#define CURVE25519_SIZE 32
+/* Indicates that curve25519_mul conforms to RFC 7748. */
+#define NETTLE_CURVE25519_RFC7748 1
+
void
curve25519_mul_g (uint8_t *q, const uint8_t *n);
diff --git a/nettle.texinfo b/nettle.texinfo
index e539dbe6..cbcad259 100644
--- a/nettle.texinfo
+++ b/nettle.texinfo
@@ -4337,6 +4337,20 @@ by @cite{RFC 7748}. Its the output is therefore well defined for
@emph{all} possible inputs, no matter if the input string represents a
valid point on the curve or not.
+Note that the curve25519 implementation in earlier versions from Nettle
+deviates slightly from @cite{RFC 7748}, in that bit 255 of the @math{x}
+coordinate of the point input to curve25519_mul was not ignored. The
+@file{nette/curve25519.h} defines a preprocessor symbol
+@code{NETTLE_CURVE25519_RFC7748} to indicate conformance with the
+standard.
+
+Nettle defines Curve 25519 in @file{<nettle/curve25519.h>}.
+
+@defvr Constant NETTLE_CURVE25519_RFC7748
+Defined to 1 in Nettle versions conforming to RFC 7748. Undefined in
+earlier versions.
+@end defvr
+
@defvr Constant CURVE25519_SIZE
The size of the strings representing curve25519 points and scalars, 32.
@end defvr
--
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