From 2cee8ae8505553efe6285ea320f2aa8aad33fbe0 Mon Sep 17 00:00:00 2001
From: Frank Denis <github@pureftpd.org>
Date: Mon, 23 Oct 2017 00:15:52 +0200
Subject: [PATCH] Backport _crypto_sign_ed25519_small_order() changes

---
 .../crypto_sign/ed25519/ref10/open.c          | 35 ++++---------------
 1 file changed, 7 insertions(+), 28 deletions(-)

diff --git a/src/libsodium/crypto_sign/ed25519/ref10/open.c b/src/libsodium/crypto_sign/ed25519/ref10/open.c
index fa1c72d8..c32a14ff 100644
--- a/src/libsodium/crypto_sign/ed25519/ref10/open.c
+++ b/src/libsodium/crypto_sign/ed25519/ref10/open.c
@@ -34,7 +34,7 @@ crypto_sign_check_S_lt_L(const unsigned char *S)
 }
 
 int
-_crypto_sign_ed25519_small_order(const unsigned char p[32])
+_crypto_sign_ed25519_small_order(const unsigned char s[32])
 {
     CRYPTO_ALIGN(16)
     static const unsigned char blacklist[][32] = {
@@ -57,48 +57,27 @@ _crypto_sign_ed25519_small_order(const unsigned char p[32])
           0x76, 0x0d, 0x10, 0x67, 0x0f, 0x2a, 0x20, 0x53, 0xfa, 0x2c, 0x39,
           0xcc, 0xc6, 0x4e, 0xc7, 0xfd, 0x77, 0x92, 0xac, 0x03, 0x7a },
         /* p-1 (order 2) */
-        { 0x13, 0xe8, 0x95, 0x8f, 0xc2, 0xb2, 0x27, 0xb0, 0x45, 0xc3, 0xf4,
-          0x89, 0xf2, 0xef, 0x98, 0xf0, 0xd5, 0xdf, 0xac, 0x05, 0xd3, 0xc6,
-          0x33, 0x39, 0xb1, 0x38, 0x02, 0x88, 0x6d, 0x53, 0xfc, 0x85 },
-        /* p (order 4) */
-        { 0xb4, 0x17, 0x6a, 0x70, 0x3d, 0x4d, 0xd8, 0x4f, 0xba, 0x3c, 0x0b,
-          0x76, 0x0d, 0x10, 0x67, 0x0f, 0x2a, 0x20, 0x53, 0xfa, 0x2c, 0x39,
-          0xcc, 0xc6, 0x4e, 0xc7, 0xfd, 0x77, 0x92, 0xac, 0x03, 0xfa },
-        /* p+1 (order 1) */
         { 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+2707385501144840649318225287225658788936804267575313519463743609750303402022
-           (order 8) */
+        /* 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+55188659117513257062467267217118295137698188065244968500265048394206261417927
-           (order 8) */
+        /* 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 },
-        /* 2p-1 (order 2) */
-        { 0xd9, 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, 0xff },
-        /* 2p (order 4) */
-        { 0xda, 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, 0xff },
-        /* 2p+1 (order 1) */
-        { 0xdb, 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, 0xff }
+          0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f }
     };
     size_t        i, j;
     unsigned char c;
 
     for (i = 0; i < sizeof blacklist / sizeof blacklist[0]; i++) {
         c = 0;
-        for (j = 0; j < 32; j++) {
-            c |= p[j] ^ blacklist[i][j];
+        for (j = 0; j < 31; j++) {
+            c |= s[j] ^ blacklist[i][j];
         }
+        c |= (s[j] & 0x7f) ^ blacklist[i][j];
         if (c == 0) {
             return 1;
         }