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