From: tb <tb@openbsd.org>
Date: Thu, 24 Nov 2022 16:34:13 +0000 (+0000)
Subject: Simplify y_bit handling in compressed coordinates
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=1877f4c78ed7f69ec32c466546a6b3a07622d685;p=openbsd

Simplify y_bit handling in compressed coordinates

If y_bit is set for a zero y, something is wrong and we can error directly.
No need to run the non-trivial BN_kronecker() to check if BN_mod_sqrt()
lied or not, only to set a more specific error code.

ok jsing
---

diff --git a/lib/libcrypto/ec/ecp_oct.c b/lib/libcrypto/ec/ecp_oct.c
index 7c29e7e6128..5e3484e2bcf 100644
--- a/lib/libcrypto/ec/ecp_oct.c
+++ b/lib/libcrypto/ec/ecp_oct.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ecp_oct.c,v 1.16 2022/11/19 07:29:29 tb Exp $ */
+/* $OpenBSD: ecp_oct.c,v 1.17 2022/11/24 16:34:13 tb Exp $ */
 /* Includes code written by Lenka Fibikova <fibikova@exp-math.uni-essen.de>
  * for the OpenSSL project.
  * Includes code written by Bodo Moeller for the OpenSSL project.
@@ -162,20 +162,7 @@ ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group,
 	}
 	if (y_bit != BN_is_odd(y)) {
 		if (BN_is_zero(y)) {
-			int kron;
-
-			kron = BN_kronecker(x, &group->field, ctx);
-			if (kron == -2)
-				goto err;
-
-			if (kron == 1)
-				ECerror(EC_R_INVALID_COMPRESSION_BIT);
-			else
-				/*
-				 * BN_mod_sqrt() should have cought this
-				 * error (not a square)
-				 */
-				ECerror(EC_R_INVALID_COMPRESSED_POINT);
+			ECerror(EC_R_INVALID_COMPRESSION_BIT);
 			goto err;
 		}
 		if (!BN_usub(y, &group->field, y))