From 2a03b7cb56aaed711ed59aee8972dbd1c4129344 Mon Sep 17 00:00:00 2001
From: tb <>
Date: Wed, 22 Jan 2025 10:08:10 +0000
Subject: Split BN_mod_sqr_reciprocal() out of BN_mod_mul_reciprocal()

There's no need for BN_mod_mul_reciprocal() to have this complication.
The caller knows when x == y, so place the burden on the caller. This
simplifies both the caller side and the implementation in bn_recp.c.

ok jsing
---
 src/lib/libcrypto/bn/bn_exp.c   |  8 ++++----
 src/lib/libcrypto/bn/bn_local.h |  4 +++-
 src/lib/libcrypto/bn/bn_recp.c  | 30 ++++++++++++------------------
 3 files changed, 19 insertions(+), 23 deletions(-)

(limited to 'src')

diff --git a/src/lib/libcrypto/bn/bn_exp.c b/src/lib/libcrypto/bn/bn_exp.c
index 8ff518e938..129c12495c 100644
--- a/src/lib/libcrypto/bn/bn_exp.c
+++ b/src/lib/libcrypto/bn/bn_exp.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_exp.c,v 1.54 2025/01/21 15:44:22 tb Exp $ */
+/* $OpenBSD: bn_exp.c,v 1.55 2025/01/22 10:08:10 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -1023,7 +1023,7 @@ BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
 
 	window = BN_window_bits_for_exponent_size(bits);
 	if (window > 1) {
-		if (!BN_mod_mul_reciprocal(aa, val[0], val[0], recp, ctx))
+		if (!BN_mod_sqr_reciprocal(aa, val[0], recp, ctx))
 			goto err;
 		j = 1 << (window - 1);
 		for (i = 1; i < j; i++) {
@@ -1047,7 +1047,7 @@ BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
 	for (;;) {
 		if (BN_is_bit_set(q, wstart) == 0) {
 			if (!start)
-				if (!BN_mod_mul_reciprocal(r, r, r, recp, ctx))
+				if (!BN_mod_sqr_reciprocal(r, r, recp, ctx))
 					goto err;
 			if (wstart == 0)
 				break;
@@ -1076,7 +1076,7 @@ BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
 		/* add the 'bytes above' */
 		if (!start)
 			for (i = 0; i < j; i++) {
-				if (!BN_mod_mul_reciprocal(r, r, r, recp, ctx))
+				if (!BN_mod_sqr_reciprocal(r, r, recp, ctx))
 					goto err;
 			}
 
diff --git a/src/lib/libcrypto/bn/bn_local.h b/src/lib/libcrypto/bn/bn_local.h
index 2042e0b193..d9389995f7 100644
--- a/src/lib/libcrypto/bn/bn_local.h
+++ b/src/lib/libcrypto/bn/bn_local.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_local.h,v 1.46 2025/01/21 15:44:22 tb Exp $ */
+/* $OpenBSD: bn_local.h,v 1.47 2025/01/22 10:08:10 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -277,6 +277,8 @@ int	BN_div_recp(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, BN_RECP_CTX *recp,
     BN_CTX *ctx);
 int	BN_mod_mul_reciprocal(BIGNUM *r, const BIGNUM *x, const BIGNUM *y,
     BN_RECP_CTX *recp, BN_CTX *ctx);
+int	BN_mod_sqr_reciprocal(BIGNUM *r, const BIGNUM *x, BN_RECP_CTX *recp,
+    BN_CTX *ctx);
 int	BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
     const BIGNUM *m, BN_CTX *ctx);
 
diff --git a/src/lib/libcrypto/bn/bn_recp.c b/src/lib/libcrypto/bn/bn_recp.c
index 8dd6b8af65..bf38380710 100644
--- a/src/lib/libcrypto/bn/bn_recp.c
+++ b/src/lib/libcrypto/bn/bn_recp.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_recp.c,v 1.27 2025/01/22 09:39:56 tb Exp $ */
+/* $OpenBSD: bn_recp.c,v 1.28 2025/01/22 10:08:10 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -230,24 +230,18 @@ int
 BN_mod_mul_reciprocal(BIGNUM *r, const BIGNUM *x, const BIGNUM *y,
     BN_RECP_CTX *recp, BN_CTX *ctx)
 {
-	int ret = 0;
-	BIGNUM *a;
+	if (!BN_mul(r, x, y, ctx))
+		return 0;
 
-	BN_CTX_start(ctx);
-	if ((a = BN_CTX_get(ctx)) == NULL)
-		goto err;
-
-	if (x == y) {
-		if (!BN_sqr(a, x, ctx))
-			goto err;
-	} else {
-		if (!BN_mul(a, x, y, ctx))
-			goto err;
-	}
+	return BN_div_recp(NULL, r, r, recp, ctx);
+}
 
-	ret = BN_div_recp(NULL, r, a, recp, ctx);
+/* Compute r = x^2 % m. */
+int
+BN_mod_sqr_reciprocal(BIGNUM *r, const BIGNUM *x, BN_RECP_CTX *recp, BN_CTX *ctx)
+{
+	if (!BN_sqr(r, x, ctx))
+		return 0;
 
-err:
-	BN_CTX_end(ctx);
-	return ret;
+	return BN_div_recp(NULL, r, r, recp, ctx);
 }
-- 
cgit v1.2.3-55-g6feb