From 15649c5849fa15674550a8250c2937c4304dc9bb Mon Sep 17 00:00:00 2001
From: Frank Denis <github@pureftpd.org>
Date: Mon, 23 Oct 2017 00:00:25 +0200
Subject: [PATCH] + ge_is_less_than_p()

---
 .../curve25519/ref10/curve25519_ref10.c       | 21 +++++++++++++++++--
 .../include/sodium/private/curve25519_ref10.h |  2 ++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/src/libsodium/crypto_core/curve25519/ref10/curve25519_ref10.c b/src/libsodium/crypto_core/curve25519/ref10/curve25519_ref10.c
index 818406ce..a7c174f3 100644
--- a/src/libsodium/crypto_core/curve25519/ref10/curve25519_ref10.c
+++ b/src/libsodium/crypto_core/curve25519/ref10/curve25519_ref10.c
@@ -2126,6 +2126,23 @@ ge_is_on_main_subgroup(const ge_p3 *p)
     return fe_iszero(pl.X);
 }
 
+int
+ge_is_less_than_p(const unsigned char *s)
+{
+    unsigned char c;
+    unsigned char d;
+    unsigned int  i;
+
+    c = (s[31] & 0x7f) ^ 0x7f;
+    for (i = 30; i > 0; i--) {
+        c |= s[i] ^ 0xff;
+    }
+    c = (((unsigned int) c) - 1U) >> 8;
+    d = (0xed - 1U - (unsigned int) s[0]) >> 8;
+
+    return 1 - (c & d & 1);
+}
+
 int
 ge_has_small_order(const unsigned char s[32])
 {
@@ -2153,11 +2170,11 @@ ge_has_small_order(const unsigned char s[32])
         { 0xec, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
           0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
           0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f },
-        /* p (order 4) */
+        /* p (=0, order 4) */
         { 0xed, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
           0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
           0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f },
-        /* p+1 (order 2) */
+        /* p+1 (=1, order 1) */
         { 0xee, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
           0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
           0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f }
diff --git a/src/libsodium/include/sodium/private/curve25519_ref10.h b/src/libsodium/include/sodium/private/curve25519_ref10.h
index f153a8ff..3533957b 100644
--- a/src/libsodium/include/sodium/private/curve25519_ref10.h
+++ b/src/libsodium/include/sodium/private/curve25519_ref10.h
@@ -104,6 +104,7 @@ typedef struct {
 #define ge_scalarmult_base crypto_core_curve25519_ref10_ge_scalarmult_base
 #define ge_double_scalarmult_vartime crypto_core_curve25519_ref10_ge_double_scalarmult_vartime
 #define ge_scalarmult_vartime crypto_core_curve25519_ref10_ge_scalarmult_vartime
+#define ge_is_less_than_p crypto_core_curve25519_ref10_ge_is_less_than_p
 #define ge_is_on_curve crypto_core_curve25519_ref10_ge_is_on_curve
 #define ge_is_on_main_subgroup crypto_core_curve25519_ref10_ge_is_on_main_subgroup
 #define ge_has_small_order crypto_core_curve25519_ref10_ge_has_small_order
@@ -120,6 +121,7 @@ extern void ge_scalarmult_base(ge_p3 *,const unsigned char *);
 extern void ge_double_scalarmult_vartime(ge_p2 *,const unsigned char *,const ge_p3 *,const unsigned char *);
 extern void ge_scalarmult(ge_p3 *,const unsigned char *,const ge_p3 *);
 extern void ge_scalarmult_vartime(ge_p3 *,const unsigned char *,const ge_p3 *);
+extern int ge_is_less_than_p(const unsigned char *s);
 extern int ge_is_on_curve(const ge_p3 *p);
 extern int ge_is_on_main_subgroup(const ge_p3 *p);
 extern int ge_has_small_order(const unsigned char s[32]);