From 8be6a4ed02297f380bbea269f2e1c08a592444bc Mon Sep 17 00:00:00 2001
From: David Benjamin
Date: Thu, 30 May 2019 17:01:10 -0400
Subject: [PATCH] Fix various mistakes in ec_GFp_nistp_recode_scalar_bits
comment.
Reviewed-by: Nicola Tuveri
Reviewed-by: Matt Caswell
(Merged from https://github.com/openssl/openssl/pull/9050)
---
crypto/ec/ecp_nistputil.c | 24 ++++++++++++------------
1 file changed, 12 insertions(+), 12 deletions(-)
diff --git a/crypto/ec/ecp_nistputil.c b/crypto/ec/ecp_nistputil.c
index 82cca66b0d..0715370b51 100644
--- a/crypto/ec/ecp_nistputil.c
+++ b/crypto/ec/ecp_nistputil.c
@@ -158,13 +158,13 @@ void ec_GFp_nistp_points_make_affine_internal(size_t num, void *point_array,
* of a nonnegative integer (b_k in {0, 1}), rewrite it in digits 0, 1, -1
* by using bit-wise subtraction as follows:
*
- * b_k b_(k-1) ... b_2 b_1 b_0
- * - b_k ... b_3 b_2 b_1 b_0
- * -------------------------------------
- * s_k b_(k-1) ... s_3 s_2 s_1 s_0
+ * b_k b_(k-1) ... b_2 b_1 b_0
+ * - b_k ... b_3 b_2 b_1 b_0
+ * -----------------------------------------
+ * s_(k+1) s_k ... s_3 s_2 s_1 s_0
*
* A left-shift followed by subtraction of the original value yields a new
- * representation of the same value, using signed bits s_i = b_(i+1) - b_i.
+ * representation of the same value, using signed bits s_i = b_(i-1) - b_i.
* This representation from Booth's paper has since appeared in the
* literature under a variety of different names including "reversed binary
* form", "alternating greedy expansion", "mutual opposite form", and
@@ -188,7 +188,7 @@ void ec_GFp_nistp_points_make_affine_internal(size_t num, void *point_array,
* (1961), pp. 67-91), in a radix-2^5 setting. That is, we always combine five
* signed bits into a signed digit:
*
- * s_(4j + 4) s_(4j + 3) s_(4j + 2) s_(4j + 1) s_(4j)
+ * s_(5j + 4) s_(5j + 3) s_(5j + 2) s_(5j + 1) s_(5j)
*
* The sign-alternating property implies that the resulting digit values are
* integers from -16 to 16.
@@ -196,14 +196,14 @@ void ec_GFp_nistp_points_make_affine_internal(size_t num, void *point_array,
* Of course, we don't actually need to compute the signed digits s_i as an
* intermediate step (that's just a nice way to see how this scheme relates
* to the wNAF): a direct computation obtains the recoded digit from the
- * six bits b_(4j + 4) ... b_(4j - 1).
+ * six bits b_(5j + 4) ... b_(5j - 1).
*
- * This function takes those five bits as an integer (0 .. 63), writing the
+ * This function takes those six bits as an integer (0 .. 63), writing the
* recoded digit to *sign (0 for positive, 1 for negative) and *digit (absolute
- * value, in the range 0 .. 8). Note that this integer essentially provides the
- * input bits "shifted to the left" by one position: for example, the input to
- * compute the least significant recoded digit, given that there's no bit b_-1,
- * has to be b_4 b_3 b_2 b_1 b_0 0.
+ * value, in the range 0 .. 16). Note that this integer essentially provides
+ * the input bits "shifted to the left" by one position: for example, the input
+ * to compute the least significant recoded digit, given that there's no bit
+ * b_-1, has to be b_4 b_3 b_2 b_1 b_0 0.
*
*/
void ec_GFp_nistp_recode_scalar_bits(unsigned char *sign,
--
2.34.1