From 74ee0e82b6891e090f20723750faeb19064e31b2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Niels=20M=C3=B6ller?= <nisse@lysator.liu.se>
Date: Sat, 13 Mar 2021 15:19:19 +0100
Subject: [PATCH] Fix bug in ecc_ecdsa_verify.

* ecc-ecdsa-verify.c (ecc_ecdsa_verify): Use ecc_mod_mul_canonical
to compute the scalars used for ecc multiplication.
* testsuite/ecdsa-verify-test.c (test_main): Add test case that
triggers an assert on 64-bit platforms, without above fix.
* testsuite/ecdsa-sign-test.c (test_main): Test case generating
the same signature.

(cherry picked from commit 2397757b3f95fcae1e2d3011bf99ca5b5438378f)
---
 ChangeLog                     | 10 +++++++++-
 ecc-ecdsa-verify.c            |  4 ++--
 testsuite/ecdsa-sign-test.c   | 13 +++++++++++++
 testsuite/ecdsa-verify-test.c | 20 ++++++++++++++++++++
 4 files changed, 44 insertions(+), 3 deletions(-)

#diff --git a/ChangeLog b/ChangeLog
#index 2a9217a6..63848f53 100644
#--- a/ChangeLog
#+++ b/ChangeLog
#@@ -1,7 +1,15 @@
# 2021-03-13  Niels Möller  <nisse@lysator.liu.se>
# 
#-	* eddsa-verify.c (equal_h): Use ecc_mod_mul_canonical.
#+	* ecc-ecdsa-verify.c (ecc_ecdsa_verify): Use ecc_mod_mul_canonical
#+	to compute the scalars used for ecc multiplication.
#+	* testsuite/ecdsa-verify-test.c (test_main): Add test case that
#+	triggers an assert on 64-bit platforms, without above fix.
#+	* testsuite/ecdsa-sign-test.c (test_main): Test case generating
#+	the same signature.
#+
#+2021-03-13  Niels Möller  <nisse@lysator.liu.se>
# 
#+	* eddsa-verify.c (equal_h): Use ecc_mod_mul_canonical.
# 2021-03-11  Niels Möller  <nisse@lysator.liu.se>
# 
# 	* ecc-mod-arith.c (ecc_mod_mul_canonical, ecc_mod_sqr_canonical):
--- a/ecc-ecdsa-verify.c
+++ b/ecc-ecdsa-verify.c
@@ -102,10 +102,10 @@ ecc_ecdsa_verify (const struct ecc_curve
 
   /* u1 = h / s, P1 = u1 * G */
   ecc_hash (&ecc->q, hp, length, digest);
-  ecc_mod_mul (&ecc->q, u1, hp, sinv);
+  ecc_mod_mul_canonical (&ecc->q, u1, hp, sinv, u1);
 
   /* u2 = r / s, P2 = u2 * Y */
-  ecc_mod_mul (&ecc->q, u2, rp, sinv);
+  ecc_mod_mul_canonical (&ecc->q, u2, rp, sinv, u2);
 
    /* Total storage: 5*ecc->p.size + ecc->mul_itch */
   ecc->mul (ecc, P2, u2, pp, u2 + ecc->p.size);
--- a/testsuite/ecdsa-sign-test.c
+++ b/testsuite/ecdsa-sign-test.c
@@ -58,6 +58,19 @@ test_ecdsa (const struct ecc_curve *ecc,
 void
 test_main (void)
 {
+  /* Producing the signature for corresponding test in
+     ecdsa-verify-test.c, with special u1 and u2. */
+  test_ecdsa (&_nettle_secp_224r1,
+	      "99b5b787484def12894ca507058b3bf5"
+	      "43d72d82fa7721d2e805e5e6",
+	      "2",
+	      SHEX("cdb887ac805a3b42e22d224c85482053"
+		   "16c755d4a736bb2032c92553"),
+	      "706a46dc76dcb76798e60e6d89474788"
+	      "d16dc18032d268fd1a704fa6", /* r */
+	      "3a41e1423b1853e8aa89747b1f987364"
+	      "44705d6d6d8371ea1f578f2e"); /* s */
+
   /* Test cases for the smaller groups, verified with a
      proof-of-concept implementation done for Yubico AB. */
   /* From RFC 4754 */
--- a/testsuite/ecdsa-verify-test.c
+++ b/testsuite/ecdsa-verify-test.c
@@ -81,6 +81,26 @@ test_ecdsa (const struct ecc_curve *ecc,
 void
 test_main (void)
 {
+  /* Corresponds to nonce k = 2 and private key z =
+     0x99b5b787484def12894ca507058b3bf543d72d82fa7721d2e805e5e6. z and
+     hash are chosen so that intermediate scalars in the verify
+     equations are u1 = 0x6b245680e700, u2 =
+     259da6542d4ba7d21ad916c3bd57f811. These values require canonical
+     reduction of the scalars. Bug caused by missing canonical
+     reduction reported by Guido Vranken. */
+  test_ecdsa (&_nettle_secp_224r1,
+	      "9e7e6cc6b1bdfa8ee039b66ad85e5490"
+	      "7be706a900a3cba1c8fdd014", /* x */
+	      "74855db3f7c1b4097ae095745fc915e3"
+	      "8a79d2a1de28f282eafb22ba", /* y */
+
+	      SHEX("cdb887ac805a3b42e22d224c85482053"
+		   "16c755d4a736bb2032c92553"),
+	      "706a46dc76dcb76798e60e6d89474788"
+	      "d16dc18032d268fd1a704fa6", /* r */
+	      "3a41e1423b1853e8aa89747b1f987364"
+	      "44705d6d6d8371ea1f578f2e"); /* s */
+
   /* From RFC 4754 */
   test_ecdsa (&_nettle_secp_256r1,
 	      "2442A5CC 0ECD015F A3CA31DC 8E2BBC70"
