X-Git-Url: https://bearssl.org/gitweb//home/git/?p=BearSSL;a=blobdiff_plain;f=src%2Fint%2Fi15_ext2.c;fp=src%2Fint%2Fi15_ext2.c;h=84fc2d633656f80373dae49e7f64c558466e7bb9;hp=0000000000000000000000000000000000000000;hb=28e4e120b84dacdf53963639f1a8a6fec2793662;hpb=6dd8c51ba7e8ca106ede7ff58b5c507042bbf6eb

diff --git a/src/int/i15_ext2.c b/src/int/i15_ext2.c
new file mode 100644
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--- /dev/null
+++ b/src/int/i15_ext2.c
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+/*
+ * 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 RSA.
+ */
+
+/* see inner.h */
+void
+br_i15_decode_reduce(uint16_t *x,
+	const void *src, size_t len, const uint16_t *m)
+{
+	uint32_t m_ebitlen, m_rbitlen;
+	size_t mblen, k;
+	const unsigned char *buf;
+	uint32_t acc;
+	int acc_len;
+
+	/*
+	 * Get the encoded bit length.
+	 */
+	m_ebitlen = m[0];
+
+	/*
+	 * Special case for an invalid (null) modulus.
+	 */
+	if (m_ebitlen == 0) {
+		x[0] = 0;
+		return;
+	}
+
+	/*
+	 * Clear the destination.
+	 */
+	br_i15_zero(x, m_ebitlen);
+
+	/*
+	 * First decode directly as many bytes as possible. This requires
+	 * computing the actual bit length.
+	 */
+	m_rbitlen = m_ebitlen >> 4;
+	m_rbitlen = (m_ebitlen & 15) + (m_rbitlen << 4) - m_rbitlen;
+	mblen = (m_rbitlen + 7) >> 3;
+	k = mblen - 1;
+	if (k >= len) {
+		br_i15_decode(x, src, len);
+		x[0] = m_ebitlen;
+		return;
+	}
+	buf = src;
+	br_i15_decode(x, buf, k);
+	x[0] = m_ebitlen;
+
+	/*
+	 * Input remaining bytes, using 15-bit words.
+	 */
+	acc = 0;
+	acc_len = 0;
+	while (k < len) {
+		uint32_t v;
+
+		v = buf[k ++];
+		acc = (acc << 8) | v;
+		acc_len += 8;
+		if (acc_len >= 15) {
+			br_i15_muladd_small(x, acc >> (acc_len - 15), m);
+			acc_len -= 15;
+			acc &= ~((uint32_t)-1 << acc_len);
+		}
+	}
+
+	/*
+	 * We may have some bits accumulated. We then perform a shift to
+	 * be able to inject these bits as a full 15-bit word.
+	 */
+	if (acc_len != 0) {
+		acc = (acc | (x[1] << acc_len)) & 0x7FFF;
+		br_i15_rshift(x, 15 - acc_len);
+		br_i15_muladd_small(x, acc, m);
+	}
+}
+
+/* see inner.h */
+void
+br_i15_reduce(uint16_t *x, const uint16_t *a, const uint16_t *m)
+{
+	uint32_t m_bitlen, a_bitlen;
+	size_t mlen, alen, u;
+
+	m_bitlen = m[0];
+	mlen = (m_bitlen + 15) >> 4;
+
+	x[0] = m_bitlen;
+	if (m_bitlen == 0) {
+		return;
+	}
+
+	/*
+	 * If the source is shorter, then simply copy all words from a[]
+	 * and zero out the upper words.
+	 */
+	a_bitlen = a[0];
+	alen = (a_bitlen + 15) >> 4;
+	if (a_bitlen < m_bitlen) {
+		memcpy(x + 1, a + 1, alen * sizeof *a);
+		for (u = alen; u < mlen; u ++) {
+			x[u + 1] = 0;
+		}
+		return;
+	}
+
+	/*
+	 * The source length is at least equal to that of the modulus.
+	 * We must thus copy N-1 words, and input the remaining words
+	 * one by one.
+	 */
+	memcpy(x + 1, a + 2 + (alen - mlen), (mlen - 1) * sizeof *a);
+	x[mlen] = 0;
+	for (u = 1 + alen - mlen; u > 0; u --) {
+		br_i15_muladd_small(x, a[u], m);
+	}
+}
+
+/* see inner.h */
+void
+br_i15_mulacc(uint16_t *d, const uint16_t *a, const uint16_t *b)
+{
+	size_t alen, blen, u;
+
+	alen = (a[0] + 15) >> 4;
+	blen = (b[0] + 15) >> 4;
+	d[0] = a[0] + b[0];
+	for (u = 0; u < blen; u ++) {
+		uint32_t f;
+		size_t v;
+		uint32_t cc;
+
+		f = b[1 + u];
+		cc = 0;
+		for (v = 0; v < alen; v ++) {
+			uint32_t z;
+
+			z = (uint32_t)d[1 + u + v] + MUL15(f, a[1 + v]) + cc;
+			cc = z >> 15;
+			d[1 + u + v] = z & 0x7FFF;
+		}
+		d[1 + u + alen] = cc;
+	}
+}