+/* p192.c */
+/*
+ This file is part of the AVR-Crypto-Lib.
+ Copyright (C) 2006-2012 Daniel Otte (daniel.otte@rub.de)
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <inttypes.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "bigint.h"
+
+/*
+ * p = 6277101735386680763835789423207666416083908700390324961279
+ * = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFFFFFFFFFFFF
+ */
+
+static
+uint8_t nist_curve_p192_p_w[] = {
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xfe, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
+};
+
+bigint_t nist_curve_p192_p = {
+ .length_W = 192 / BIGINT_WORD_SIZE,
+ .wordv = nist_curve_p192_p_w,
+ .info = 7
+};
+
+/*
+ * A = ( A5 || A4 || A3 || A2 || A1 || A0 ) ; An if 64-bit
+ * A mod p = B = T + S1 + S2 + S3 mod p
+ *
+ * T = ( A2 || A1 || A0 )
+ * S1 = ( A3 || A3 )
+ * S2 = ( A4 || A4 || 0 )
+ * S3 = ( A5 || A5 || A5 )
+ *
+ */
+
+int bigint_reduce_p192(bigint_t *a){
+
+ bigint_word_t s_w[3 * 64 / BIGINT_WORD_SIZE];
+ bigint_t s;
+ uint16_t o_length;
+
+ o_length = a->length_W;
+
+ if(o_length < 192 / BIGINT_WORD_SIZE){
+ return 0;
+ }
+
+ if(o_length > 192 * 2 / BIGINT_WORD_SIZE){
+ bigint_reduce(a, &nist_curve_p192_p);
+ }
+
+ if(o_length > 192 / BIGINT_WORD_SIZE){
+ s.wordv = s_w;
+ s.length_W = 2 * 64 / BIGINT_WORD_SIZE;
+
+ /*
+ * copy A3 twice in s
+ */
+ if(o_length >= 4 * 64 / BIGINT_WORD_SIZE){
+ memcpy(s.wordv, a->wordv + 3 * 64 / BIGINT_WORD_SIZE, 64 / 8);
+ }else{
+ memset(s.wordv, 0, 8);
+ memcpy(s.wordv, a->wordv + 3 * 64 / BIGINT_WORD_SIZE,
+ o_length * BIGINT_WORD_SIZE / 8 - 3 * 64 / 8);
+ }
+
+ memcpy(s.wordv + 64 / BIGINT_WORD_SIZE, s.wordv, 64 / 8);
+ bigint_adjust(&s);
+
+ /*
+ * Set A3 to zero so we can use a as T
+ */
+ memset(a->wordv + 3 * 64 / BIGINT_WORD_SIZE, 0, BIGINT_WORD_SIZE / 8);
+ a->length_W = 3 * 64 / BIGINT_WORD_SIZE;
+ bigint_adjust(a);
+
+ /*
+ * Add s (alias S1) to a (alias T)
+ */
+ bigint_add_u(a, a, &s);
+
+
+ if(o_length > 4 * 64 / BIGINT_WORD_SIZE){
+ /*
+ * copy A4 twice in s
+ */
+ if(o_length >= 5 * 64 / BIGINT_WORD_SIZE){
+ memcpy(s.wordv, a->wordv + 4 * 64 / BIGINT_WORD_SIZE, 64 / 8);
+ }else{
+ memset(s.wordv, 0, 8);
+ memcpy(s.wordv, a->wordv + 4 * 64 / BIGINT_WORD_SIZE,
+ o_length * BIGINT_WORD_SIZE / 8 - 4 * 64 / 8);
+ }
+ memcpy(s.wordv + 64 / BIGINT_WORD_SIZE, s.wordv, 64 / 8);
+ bigint_adjust(&s);
+
+ /*
+ * Add s (alias S2) to a (alias T + S1)
+ */
+ bigint_add_scale_u(a, &s, 8);
+
+
+ if(o_length > 5 * 64 / BIGINT_WORD_SIZE){
+ /*
+ * copy A5 three times in s
+ */
+ if(o_length == 6 * 64 / BIGINT_WORD_SIZE){
+ memcpy(s.wordv, a->wordv + 5 * 64 / BIGINT_WORD_SIZE, 64 / 8);
+ } else {
+ memset(s.wordv, 0, 8);
+ memcpy(s.wordv, a->wordv + 5 * 64 / BIGINT_WORD_SIZE,
+ o_length * BIGINT_WORD_SIZE / 8 - 5 * 64 / 8);
+ }
+ memcpy(s.wordv + 64 / BIGINT_WORD_SIZE, s.wordv, 64 / 8);
+ memcpy(s.wordv + 2 * 64 / BIGINT_WORD_SIZE, s.wordv, 64 / 8);
+ s.length_W = 3 * 64 / BIGINT_WORD_SIZE;
+ bigint_adjust(&s);
+
+ /*
+ * Add s (alias S2) to a (alias T + S1)
+ */
+ bigint_add_u(a, a, &s);
+ }
+ }
+
+ }
+ while(bigint_cmp_u(a, &nist_curve_p192_p) >= 0){
+ bigint_sub_u(a, a, &nist_curve_p192_p);
+ }
+
+ return 0;
+}
+