New "i15" implementation of big integers (faster, and constant-time, on ARM Cortex M0/M0+); imported into EC, ECDSA, RSA.

src/int/i15_ext1.c

@@ -0,0 +1,136 @@
+/*
+ * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining 
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be 
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "inner.h"
+
+/*
+ * This file contains some additional functions for "i15" big integers.
+ * These functions are needed to support ECDSA.
+ */
+
+/* see inner.h */
+void
+br_i15_rshift(uint16_t *x, int count)
+{
+	size_t u, len;
+	unsigned r;
+
+	len = (x[0] + 15) >> 4;
+	if (len == 0) {
+		return;
+	}
+	r = x[1] >> count;
+	for (u = 2; u <= len; u ++) {
+		unsigned w;
+
+		w = x[u];
+		x[u - 1] = ((w << (15 - count)) | r) & 0x7FFF;
+		r = w >> count;
+	}
+	x[len] = r;
+}
+
+/* see inner.h */
+uint32_t
+br_i15_bit_length(uint16_t *x, size_t xlen)
+{
+	uint32_t tw, twk;
+
+	tw = 0;
+	twk = 0;
+	while (xlen -- > 0) {
+		uint32_t w, c;
+
+		c = EQ(tw, 0);
+		w = x[xlen];
+		tw = MUX(c, w, tw);
+		twk = MUX(c, (uint32_t)xlen, twk);
+	}
+	return (twk << 4) + BIT_LENGTH(tw);
+}
+
+/* see inner.h */
+void
+br_i15_decode(uint16_t *x, const void *src, size_t len)
+{
+	const unsigned char *buf;
+	size_t v;
+	uint32_t acc;
+	int acc_len;
+
+	buf = src;
+	v = 1;
+	acc = 0;
+	acc_len = 0;
+	while (len -- > 0) {
+		uint32_t b;
+
+		b = buf[len];
+		acc |= (b << acc_len);
+		acc_len += 8;
+		if (acc_len >= 15) {
+			x[v ++] = acc & 0x7FFF;
+			acc_len -= 15;
+			acc >>= 15;
+		}
+	}
+	if (acc_len != 0) {
+		x[v ++] = acc;
+	}
+	x[0] = br_i15_bit_length(x + 1, v - 1);
+}
+
+/* see inner.h */
+void
+br_i15_from_monty(uint16_t *x, const uint16_t *m, uint16_t m0i)
+{
+	size_t len, u, v;
+
+	len = (m[0] + 15) >> 4;
+	for (u = 0; u < len; u ++) {
+		uint32_t f, cc;
+
+		f = MUL15(x[1], m0i) & 0x7FFF;
+		cc = 0;
+		for (v = 0; v < len; v ++) {
+			uint32_t z;
+
+			z = (uint32_t)x[v + 1] + MUL15(f, m[v + 1]) + cc;
+			cc = z >> 15;
+			if (v != 0) {
+				x[v] = z & 0x7FFF;
+			}
+		}
+		x[len] = cc;
+	}
+
+	/*
+	 * We may have to do an extra subtraction, but only if the
+	 * value in x[] is indeed greater than or equal to that of m[],
+	 * which is why we must do two calls (first call computes the
+	 * carry, second call performs the subtraction only if the carry
+	 * is 0).
+	 */
+	br_i15_sub(x, m, NOT(br_i15_sub(x, m, 0)));
+}